Re: [PERFORM] Performance tuning for postgres
On Fri, Jun 4, 2010 at 12:40 AM, Yogesh Naik yogesh_n...@persistent.co.in wrote: I am performing a DB insertion and update for 3000+ records and while doing so i get CPU utilization to 100% with 67% of CPU used by postgres That sounds normal to me. What would you expect to happen? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance tuning for postgres
Yogesh Naik yogesh_n...@persistent.co.in wrote: I am performing a DB insertion and update for 3000+ records and while doing so i get CPU utilization to 100% with 67% of CPU used by postgres I have also done optimization on queries too... Is there any way to optimized the CPU utilization for postgres We'd need a lot more information before we could make useful suggestions. Knowing something about your hardware, OS, exact PostgreSQL version, postgresql.conf contents, the table definition, any foreign keys or other constraints, and exactly how you're doing the inserts would all be useful. Please read this and repost: http://wiki.postgresql.org/wiki/SlowQueryQuestions -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance tuning for postgres
In my opinion it depends on the application, the priority of the application and whether or not it is a commercially sold product, but depending on your needs you might want to consider having a 3rd party vendor who has expertise in this process review and help tune the application. One vendor that I know does this is EnterpriseDB. I've worked with other SQL engines and have a lot of experience tuning queries in a couple of the environments but PostGresql isn't one of them. Having an experienced DBA review your system can make the difference between night and day. Best Regards Michael Gould Kevin Grittner kevin.gritt...@wicourts.gov wrote: Yogesh Naik yogesh_n...@persistent.co.in wrote: I am performing a DB insertion and update for 3000+ records and while doing so i get CPU utilization to 100% with 67% of CPU used by postgres I have also done optimization on queries too... Is there any way to optimized the CPU utilization for postgres We'd need a lot more information before we could make useful suggestions. Knowing something about your hardware, OS, exact PostgreSQL version, postgresql.conf contents, the table definition, any foreign keys or other constraints, and exactly how you're doing the inserts would all be useful. Please read this and repost: http://wiki.postgresql.org/wiki/SlowQueryQuestions -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Michael Gould, Managing Partner Intermodal Software Solutions, LLC 904.226.0978 904.592.5250 fax -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance tuning for postgres
Is this a bulk insert? Are you wrapping your statements within a transaction(s)? How many columns in the table? What do the table statistics look like? On Fri, Jun 4, 2010 at 9:21 AM, Michael Gould mgo...@intermodalsoftwaresolutions.net wrote: In my opinion it depends on the application, the priority of the application and whether or not it is a commercially sold product, but depending on your needs you might want to consider having a 3rd party vendor who has expertise in this process review and help tune the application. One vendor that I know does this is EnterpriseDB. I've worked with other SQL engines and have a lot of experience tuning queries in a couple of the environments but PostGresql isn't one of them. Having an experienced DBA review your system can make the difference between night and day. Best Regards Michael Gould Kevin Grittner kevin.gritt...@wicourts.gov wrote: Yogesh Naik yogesh_n...@persistent.co.in wrote: I am performing a DB insertion and update for 3000+ records and while doing so i get CPU utilization to 100% with 67% of CPU used by postgres I have also done optimization on queries too... Is there any way to optimized the CPU utilization for postgres We'd need a lot more information before we could make useful suggestions. Knowing something about your hardware, OS, exact PostgreSQL version, postgresql.conf contents, the table definition, any foreign keys or other constraints, and exactly how you're doing the inserts would all be useful. Please read this and repost: http://wiki.postgresql.org/wiki/SlowQueryQuestions -Kevin -- Sent via pgsql-performance mailing list ( pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Michael Gould, Managing Partner Intermodal Software Solutions, LLC 904.226.0978 904.592.5250 fax -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance Tuning Large PL/PGSQL Stored Procedure
On Thu, Mar 25, 2010 at 11:56 PM, Eliot Gable egable+pgsql-performa...@gmail.com wrote: How many rows min/max/avg are coming back in your refcursors? Are you using cursors in order to return multiple complex data structures (sets, etc) in a single function call? I think the largest number of rows is around 40. Most are substantially smaller. However, most of them have about two dozen or more columns, and I have already shortened the list of columns to the minimum possible. The average number of rows is around 10, but the largest sets of rows also have the most columns. I'm using the cursors in order to obtain multiple complex data structures in a single function call. ok, small sets. yes, passing them back to the client as arrays is probably going to be faster. It's a trivial change to your proc. you have to define a type for your array element the way we are going to use it. you can use a composite type or a table (I prefer a table). create table mystuff_t ( a text, b int, c timestamptz ); create function myproc([...], mystuffs out mystuff_t[]) [inside proc] replace your cursor declaration with this: select array ( select (a,b,c)::mystuff_t from [...] ) into mystuffs; code an alternate version of the function and then inside libpq execute the query in binary and discard the results, timing the results and comparing to how you run your query now also discarding the results. we want to time it this way because from timing it from psql includes the time to print out the array in text format which we can avoid with libpqtypes (which we are not going to mess with, until we know there is a resaon to go in this direction). We do need to include the time to turn around and fetch the data from the refcursors. If you see at least a 10-20% improvement, it warrants further effort IMO (and say goodbye to refcursors forever). WITH clauses can make your queries much easier to read and yield great speedups if you need to access the table expression multiple times from other parts of the query. however, in some cases you can get into trouble because a standard set of joins is going to give the planner the most flexibility in terms of query optimization. So far, every case I have converted to WITH clauses has resulted in more than double the speed (half the time required to perform the query). The main reason appears to be from avoiding calculating JOIN conditions multiple times in different parts of the query due to the UNION and EXCEPT clauses. I have a hard time believing that unless there are other factors compromising the planner like bad statistics or a non optimal query or you are dealing with a relatively special case. 'EXCEPT' btw is also an optimization target. maybe think about converting to 'letf join where rightcol is null' or something like that. not 100% sure, I think some work was done recently on except so this advice may not be as true as it used to be, and possibly moot if the number of rows being considered by except is very small. So, you are saying that I can return a complex type as a result which contains arrays of other complex types and just use my single SELECT command to retrieve the whole data set? That would be much simpler and I imagine must faster. yes, however you will want to receive as few complex types as possible, meaning your result set should still have multiple columns. reducing the number of columns is not an optimization target. in other words, do the minimal amount of stacking necessary to allow single query extraction of data. I really am chasing milliseconds here, and I appreciate all your feedback. You've given me a relatively large number of possible optimizations I can try out. I will definitely try out the libpqtypes. That sounds like a promising way to further cut down on execution time. I think most of my performance penalty is in transfering the results back to the C++ application. yes. I've suggested libpqtypes to a number of people on the lists, and you are what i'd consider the ideal candidate. libpqtypes will completely transform the way you think about postgresql and libpq. good luck. if you need help setting it up you can email me privately or on the libpqtypes list. merlin -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance Tuning Large PL/PGSQL Stored Procedure
On 26/03/10 03:56, Eliot Gable wrote: I really am chasing milliseconds here, and I appreciate all your feedback. You've given me a relatively large number of possible optimizations I can try out. I will definitely try out the libpqtypes. That sounds like a promising way to further cut down on execution time. I think most of my performance penalty is in transfering the results back to the C++ application. In addition to all of Merlin's good advice, if the client is on a different machine to the server then try sticking wireshark or similar onto the connection. That should make it pretty clear where the main costs are in getting your data back. -- Richard Huxton Archonet Ltd -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance Tuning Large PL/PGSQL Stored Procedure
On Tue, Mar 23, 2010 at 5:00 PM, Eliot Gable egable+pgsql-performa...@gmail.com wrote: The complex type contains roughly 25 fields, mostly text, plus another 10 REFCURSORs. How many rows min/max/avg are coming back in your refcursors? Are you using cursors in order to return multiple complex data structures (sets, etc) in a single function call? The application that calls the stored procedure was also written by me in C++ and uses asynchronous libpq API commands to execute a single SQL transaction which calls the stored procedure and also performs a FETCH ALL on all open cursors. It then returns all results into various structures. All rows of all cursors that are open are always used for every call to the stored procedure. The stored procedure implements various logic which determines which tables in the database to query and how to filter the results from those queries to return only the relevant information needed by the C++ application. Currently, in terms of optimization, I have taken the following approaches based on the following reasoning: 1. For all queries whose results need to return to the C++ application, I utilize cursors so that all results can be readied and generated by the stored procedure with just one call to the PostgreSQL backend. I accomplish this using asynchronous libpq API calls to issue a single transaction to the server. The first command after the BEGIN is a SELECT * FROM MyStoredProc(blah), which is then followed by FETCH ALL commands for each cursor that the stored procedure leaves open. I then follow up with multiple API calls to return the results and retrieve the rows from those results. This minimizes the amount of back-and-forth between my C++ application and the database backend. 1a. Incidentally, I am also using cursors for most queries inside the stored procedure that do not return results to the C++ application. I am unsure whether this incurs a performance penalty compared to doing, for example, a SELECT ... INTO (var1, var2, ...) within the body of the stored procedure. Instead of using SELECT ... INTO, I am using OPEN cursor_name; FETCH cursor_name INTO (var1, var2). 2. I have built indexes on all columns that are used in where clauses and joins. 3. I use lots of joins to pull in data from various tables (there are around 60 tables that are queried with each call to the stored procedure). 4. When performing joins, the first table listed is the one that returns the most context-specific results, which always also means that it has the most-specific and fewest number of relevant rows. I then join them in order of least number of result rows with all inner joins preceding left outer joins. 5. Instead of using UNIONs and EXCEPT clauses, I use multiple WITH clauses to define several different query-specific views. I order them such that I can join additional tables in later WITH clauses to the views created WITH clauses can make your queries much easier to read and yield great speedups if you need to access the table expression multiple times from other parts of the query. however, in some cases you can get into trouble because a standard set of joins is going to give the planner the most flexibility in terms of query optimization. previously in a way that minimizes the number of rows involved in the JOIN operations while still providing provably accurate result sets. The EXCEPT clauses are then replaced by also defining one view which contains a set of IDs that I want filtered from the final result set and using a WHERE id NOT IN (SELECT id FROM filtered_view). Typically, this approach leaves me with just one UNION of two previously defined views (the union is required UNION is always an optimization target (did you mean UNION ALL?) 7. When I have a query I need to execute whose results will be used in several other queries, I currently open the cursor for that query using the FOR ... LOOP construct to retrieve all records in the result set and build a result array using the array_append() method. I then do an unnest(my_array) do not use array_append. always do array(select ...) whenever it is possible. when it isn't, rethink your problem until it is possible. only exception is to use array_agg aggregate if your problem really is an aggregation type of thing. as a matter of fact, any for...loop is an optimization target because a re-think will probably yield a query that does the same thing without paying for the loop. For most of the joins, they simply join on foreign key IDs and no additional filtering criteria are used on their information. Only a handful of the joined tables bring in additional criteria by which to filter the result set. The approach used in 7 with cursors and building a result array which is then unnested has me worried in terms of performance. It seems to me there should be some better way to accomplish the same thing. The stored procedure does not perform
Re: [PERFORM] Performance Tuning Large PL/PGSQL Stored Procedure
On Thu, Mar 25, 2010 at 10:00 PM, Merlin Moncure mmonc...@gmail.com wrote: On Tue, Mar 23, 2010 at 5:00 PM, Eliot Gable egable+pgsql-performa...@gmail.com egable%2bpgsql-performa...@gmail.com wrote: The complex type contains roughly 25 fields, mostly text, plus another 10 REFCURSORs. How many rows min/max/avg are coming back in your refcursors? Are you using cursors in order to return multiple complex data structures (sets, etc) in a single function call? I think the largest number of rows is around 40. Most are substantially smaller. However, most of them have about two dozen or more columns, and I have already shortened the list of columns to the minimum possible. The average number of rows is around 10, but the largest sets of rows also have the most columns. I'm using the cursors in order to obtain multiple complex data structures in a single function call. The application that calls the stored procedure was also written by me in C++ and uses asynchronous libpq API commands to execute a single SQL transaction which calls the stored procedure and also performs a FETCH ALL on all open cursors. It then returns all results into various structures. All rows of all cursors that are open are always used for every call to the stored procedure. The stored procedure implements various logic which determines which tables in the database to query and how to filter the results from those queries to return only the relevant information needed by the C++ application. Currently, in terms of optimization, I have taken the following approaches based on the following reasoning: 1. For all queries whose results need to return to the C++ application, I utilize cursors so that all results can be readied and generated by the stored procedure with just one call to the PostgreSQL backend. I accomplish this using asynchronous libpq API calls to issue a single transaction to the server. The first command after the BEGIN is a SELECT * FROM MyStoredProc(blah), which is then followed by FETCH ALL commands for each cursor that the stored procedure leaves open. I then follow up with multiple API calls to return the results and retrieve the rows from those results. This minimizes the amount of back-and-forth between my C++ application and the database backend. 1a. Incidentally, I am also using cursors for most queries inside the stored procedure that do not return results to the C++ application. I am unsure whether this incurs a performance penalty compared to doing, for example, a SELECT ... INTO (var1, var2, ...) within the body of the stored procedure. Instead of using SELECT ... INTO, I am using OPEN cursor_name; FETCH cursor_name INTO (var1, var2). 2. I have built indexes on all columns that are used in where clauses and joins. 3. I use lots of joins to pull in data from various tables (there are around 60 tables that are queried with each call to the stored procedure). 4. When performing joins, the first table listed is the one that returns the most context-specific results, which always also means that it has the most-specific and fewest number of relevant rows. I then join them in order of least number of result rows with all inner joins preceding left outer joins. 5. Instead of using UNIONs and EXCEPT clauses, I use multiple WITH clauses to define several different query-specific views. I order them such that I can join additional tables in later WITH clauses to the views created WITH clauses can make your queries much easier to read and yield great speedups if you need to access the table expression multiple times from other parts of the query. however, in some cases you can get into trouble because a standard set of joins is going to give the planner the most flexibility in terms of query optimization. So far, every case I have converted to WITH clauses has resulted in more than double the speed (half the time required to perform the query). The main reason appears to be from avoiding calculating JOIN conditions multiple times in different parts of the query due to the UNION and EXCEPT clauses. previously in a way that minimizes the number of rows involved in the JOIN operations while still providing provably accurate result sets. The EXCEPT clauses are then replaced by also defining one view which contains a set of IDs that I want filtered from the final result set and using a WHERE id NOT IN (SELECT id FROM filtered_view). Typically, this approach leaves me with just one UNION of two previously defined views (the union is required UNION is always an optimization target (did you mean UNION ALL?) Thanks for the suggestion on UNION ALL; I indeed do not need elimination of duplicates, so UNION ALL is a better option. 7. When I have a query I need to execute whose results will be used in several other queries, I currently open the cursor for that query using
Re: [PERFORM] performance tuning queries
First off, any thoughts per tuning inserts into large tables. I have a large table with an insert like this: insert into public.bigtab1 (text_col1, text_col2, id) values ... QUERY PLAN -- Result (cost=0.00..0.01 rows=1 width=0) (1 row) The query cost is low but this is one of the slowest statements per pgfouine Possible Causes of slow inserts : - slow triggers ? - slow foreign key checks ? (missing index on referenced table ?) - functional index on a slow function ? - crummy hardware (5 MB/s RAID cards, etc) - too many indexes ? Next we have a select count(*) that also one of the top offenders: select count(*) from public.tab3 where user_id=31 and state='A' and amount0; QUERY PLAN - Aggregate (cost=3836.53..3836.54 rows=1 width=0) - Index Scan using order_user_indx ontab3 user_id (cost=0.00..3834.29 rows=897 width=0) Index Cond: (idx_user_id = 31406948::numeric) Filter: ((state = 'A'::bpchar) AND (amount 0::numeric)) (4 rows) We have an index on the user_id but not on the state or amount, add index to amount ? Can we see EXPLAIN ANALYZE ? In this case the ideal index would be multicolumn (user_id, state) or (user_id,amount) or (user_id,state,amount) but choosing between the 3 depends on your data... You could do : SELECT count(*), state, amount0 FROM public.tab3 where user_id=31 GROUP BY state, amount0; And post the results. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] performance tuning queries
am Wed, dem 26.11.2008, um 21:21:04 -0700 mailte Kevin Kempter folgendes: Next we have a select count(*) that also one of the top offenders: select count(*) from public.tab3 where user_id=31 and state='A' and amount0; QUERY PLAN - Aggregate (cost=3836.53..3836.54 rows=1 width=0) - Index Scan using order_user_indx ontab3 user_id (cost=0.00..3834.29 rows=897 width=0) Index Cond: (idx_user_id = 31406948::numeric) Filter: ((state = 'A'::bpchar) AND (amount 0::numeric)) (4 rows) We have an index on the user_id but not on the state or amount, add index to amount ? Depends. - Is the index on user_id a unique index? - how many different values are in the table for state, i.e., maybe an index on state can help - how many rows in the table with amount 0? If almost all rows contains an amount 0 an index can't help in this case Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: - Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] performance tuning queries
Kevin Kempter schrieb: Hi All; I'm looking for tips / ideas per performance tuning some specific queries. These are generally large tables on a highly active OLTP system (100,000 - 200,000 plus queries per day) First off, any thoughts per tuning inserts into large tables. I have a large table with an insert like this: insert into public.bigtab1 (text_col1, text_col2, id) values ... QUERY PLAN -- Result (cost=0.00..0.01 rows=1 width=0) (1 row) The query cost is low but this is one of the slowest statements per pgfouine Do you insert multiple values in one transaction, or one transaction per insert? -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Performance tuning on FreeBSD
On Tue, 4 Mar 2008, Ivan Voras wrote: I'm curious about the math behind this - is ~4000 burst or sustained rate? For common BBU cache sizes (256M, 512M), filling that amount with data is pretty trivial. When the cache is full, new data can enter the cache only at a rate at which old data is evacuated from the cache (to the drive), which is at normal, uncached disk drive speeds. Should be sustained rate. The reason is if you have no BBU cache, then each transaction needs to wait for the disc to rotate around to the bit where you want to write, even though each transaction is going to be writing in approximately the same place each time. However, with a BBU cache, the system no longer needs to wait for the disc to rotate, and the writes can be made from the cache to the disc in large groups of sequential writes, which is much faster. Several transactions worth can be written on each rotation instead of just one. Matthew -- People who love sausages, respect the law, and work with IT standards shouldn't watch any of them being made. -- Peter Gutmann -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.orgextra=pgsql-performance
Re: [PERFORM] Performance tuning on FreeBSD
On Tue, 4 Mar 2008, Ivan Voras wrote: I'm curious about the math behind this - is ~4000 burst or sustained rate? Average, which is not quite burst or sustained. No math behind it, just looking at a few samples of pgbench data on similar hardware. A system like this one is profiled at http://www.kaltenbrunner.cc/blog/index.php?/archives/21-8.3-vs.-8.2-a-simple-benchmark.html for example. For common BBU cache sizes (256M, 512M), filling that amount with data is pretty trivial. I don't have any good numbers handy but I think the burst is 6000, you only get that for a few seconds before all the caches fill and the rate drops considerably. -- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.orgextra=pgsql-performance
Re: [PERFORM] Performance tuning on FreeBSD
alan bryan [EMAIL PROTECTED] wrote: I've got a new server and am myself new to tuning postgres. Server is an 8 core Xeon 2.33GHz, 8GB RAM, RAID 10 on a 3ware 9550SX-4LP w/ BBU. It's serving as the DB for a fairly write intensive (maybe 25-30%) Web application in PHP. We are not using persistent connections, thus the high max connections. I've done the following so far: cat /boot/loader.conf kern.ipc.semmni=256 kern.ipc.semmns=512 kern.ipc.semmnu=256 cat /etc/sysctl.conf kern.ipc.shmall=393216 kern.ipc.shmmax=1610612736 I would just set this to 2G (which is the max). It doesn't really hurt anything if you don't use it all. kern.ipc.semmap=256 kern.ipc.shm_use_phys=1 postgresql.conf settings (changed from Default): max_connections = 180 shared_buffers = 1024MB Why not 2G, which would be 25% of total memory? maintenance_work_mem = 128MB wal_buffers = 1024kB I then set up a test database for running pgbench with scaling factor 100. I then ran: pgbench -c 100 -t 1000 testdb and got: starting vacuum...end. transaction type: TPC-B (sort of) scaling factor: 100 number of clients: 100 number of transactions per client: 1000 number of transactions actually processed: 10/10 tps = 557.095867 (including connections establishing) tps = 558.013714 (excluding connections establishing) Just for testing, I tried turning off fsync and got: pgbench -c 100 -t 1000 testdb starting vacuum...end. transaction type: TPC-B (sort of) scaling factor: 100 number of clients: 100 number of transactions per client: 1000 number of transactions actually processed: 10/10 tps = 4014.075114 (including connections establishing) tps = 4061.662041 (excluding connections establishing) Do these numbers sound inline with what I should be seeing? What else can I do to try to get better performance in the more general sense (knowing that specifics are tied to real world data and testing). Any hints for FreeBSD specific tuning would be helpful. Are you running FreeBSD 7? If performance is of the utmost importance, then you need to be running the 7.X branch. Based on your pgbench results, I'm guessing you didn't get battery-backed cache on your systems? That makes a big difference no matter what OS you're using. Besides that, I can't think of any FreeBSD-specific things to do. Basically, general tuning advice applies to FreeBSD as well as to most other OS. -- Bill Moran Collaborative Fusion Inc. [EMAIL PROTECTED] Phone: 412-422-3463x4023 -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.orgextra=pgsql-performance
Re: [PERFORM] Performance tuning on FreeBSD
On Mon, Mar 3, 2008 at 4:26 PM, Bill Moran [EMAIL PROTECTED] wrote: cat /boot/loader.conf kern.ipc.semmni=256 kern.ipc.semmns=512 kern.ipc.semmnu=256 cat /etc/sysctl.conf kern.ipc.shmall=393216 kern.ipc.shmmax=1610612736 I would just set this to 2G (which is the max). It doesn't really hurt anything if you don't use it all. I'll try that and report back. kern.ipc.semmap=256 kern.ipc.shm_use_phys=1 postgresql.conf settings (changed from Default): max_connections = 180 shared_buffers = 1024MB Why not 2G, which would be 25% of total memory? Ditto - I'll report back. Are you running FreeBSD 7? If performance is of the utmost importance, then you need to be running the 7.X branch. Based on your pgbench results, I'm guessing you didn't get battery-backed cache on your systems? That makes a big difference no matter what OS you're using. Besides that, I can't think of any FreeBSD-specific things to do. Basically, general tuning advice applies to FreeBSD as well as to most other OS. Yes, FreeBSD 7.0-Release. Tried both the 4BSD and ULE schedulers and didn't see much difference with this test. I do have the Battery for the 3ware and it is enabled. I'll do some bonnie++ benchmarks and make sure disk is near where it should be. Should turning off fsync make things roughly 8x-10x faster? Or is that indicative of something not being correct or tuned quite right in the rest of the system? I'll have to run in production with fsync on but was just testing to see how much of an effect it had. Thanks, Alan -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.orgextra=pgsql-performance
Re: [PERFORM] Performance tuning on FreeBSD
On Mon, 3 Mar 2008, alan bryan wrote: pgbench -c 100 -t 1000 testdb tps = 558.013714 (excluding connections establishing) Just for testing, I tried turning off fsync and got: tps = 4061.662041 (excluding connections establishing) This is odd. ~500 is what I expect from this test when there is no write cache to accelerate fsync, while ~4000 is normal for your class of hardware when you have such a cache. Since you say your 3Ware card is setup with a cache and a BBU, that's suspicious--you should be able to get around 4000 with fsync on. Any chance you have the card set to write-through instead of write-back? That's the only thing that comes to mind that would cause this. -- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your Subscription: http://mail.postgresql.org/mj/mj_wwwusr?domain=postgresql.orgextra=pgsql-performance
Re: [PERFORM] Performance Tuning and Disk Cache
On 3/18/07, Barry Moore [EMAIL PROTECTED] wrote: Does anyone know how I can repeatedly run the same query in the worst case scenario of no postgres data in the disk cache (e.g., clear the page cache or force it to be ignored)? try to disconnect from postgresql, reconnect, rerun the query. if it doesn't help - you can try unmounting filesystem which contains postgresql data, and remounting it again. of course with postgresql shutdown. depesz -- http://www.depesz.com/ - nowy, lepszy depesz ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [PERFORM] Performance Tuning and Disk Cache
Barry Moore wrote: I have a very slow query that I'm trying to tune. I think my performance tuning is being complicated by the system's page cache. If a run the query after the system has been busy with other tasks for quite a long time then the query can take up to 8-10 minutes to complete. If I then rerun the same query it will complete in a couple of seconds. Does anyone know how I can repeatedly run the same query in the worst case scenario of no postgres data in the disk cache (e.g., clear the page cache or force it to be ignored)? In my experience the only 100% reliable way to do this is to reboot the machine. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Performance Tuning and Disk Cache
If you are running on a Linux kernel, try /proc/sys/vm/drop_caches. I believe the appropriate command is echo 3 /proc/sys/vm/drop_caches. Since Postgres has its own cache of data, the above followed by a PG restart should do what you are looking for. Ranga Barry Moore wrote: I have a very slow query that I'm trying to tune. I think my performance tuning is being complicated by the system's page cache. If a run the query after the system has been busy with other tasks for quite a long time then the query can take up to 8-10 minutes to complete. If I then rerun the same query it will complete in a couple of seconds. Does anyone know how I can repeatedly run the same query in the worst case scenario of no postgres data in the disk cache (e.g., clear the page cache or force it to be ignored)? In my experience the only 100% reliable way to do this is to reboot the machine. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] Performance Tuning and Disk Cache
On Sun, Mar 18, 2007 at 06:45:34AM -0600, Barry Moore wrote: Does anyone know how I can repeatedly run the same query in the worst case scenario of no postgres data in the disk cache (e.g., clear the page cache or force it to be ignored)? Depends on your OS. On linux you can run: echo 1 /proc/sys/vm/drop_caches Mike Stone ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PERFORM] Performance Tuning Article
Hi, The article seems to dismiss RAID5 a little too quickly. For many application types, using fast striped mirrors for the index space and RAID5 for the data can offer quite good performance (provided a sufficient number of spindles for the RAID5 - 5 or 6 disks or more). In fact, random read (ie most webapps) performance of RAID5 isn't necessarily worse than that of RAID10, and can in fact be better in some circumstances. And, using the cheaper RAID5 might allow you to do that separation between index and data in the first place. Just thought I'd mention it, Dmitri -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Frank Wiles Sent: Wednesday, June 22, 2005 10:52 AM To: pgsql-performance@postgresql.org Subject: [PERFORM] Performance Tuning Article Hi Everyone, I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. I believe it helps to bring together the info in a easy to digest manner. I would appreciate any feedback, comments, and especially any technical corrections. The article can be found here: http://www.revsys.com/writings/postgresql-performance.html Thanks! - Frank Wiles [EMAIL PROTECTED] http://www.wiles.org - ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Performance Tuning Article
There have been problems with Xeon processors. Can you elaborate on that please ? Thanks, -- Radu-Adrian Popescu CSA, DBA, Developer Aldrapay MD Aldratech Ltd. +40213212243 smime.p7s Description: S/MIME Cryptographic Signature
Re: [PERFORM] Performance Tuning Article
My understanding is that it isn't particularly XEON processors that is the problem Any dual processor will exhibit the problem, XEON's with hyperthreading exacerbate the problem though and the good news is that it has been fixed in 8.1 Dave On 23-Jun-05, at 8:16 AM, Keith Worthington wrote: Radu-Adrian Popescu wrote: There have been problems with Xeon processors. Can you elaborate on that please ? Thanks, Not really as I do not understand the issue. Here is one post from the archives. http://archives.postgresql.org/pgsql-performance/2005-05/msg00441.php If you search the archives for xeon sooner or later you will bump into something relevant. -- Kind Regards, Keith ---(end of broadcast)--- TIP 7: don't forget to increase your free space map settings Dave Cramer [EMAIL PROTECTED] www.postgresintl.com ICQ #14675561 jabber [EMAIL PROTECTED] ph (519 939 0336 ) ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Performance Tuning Article
On Wed, 22 Jun 2005 22:31:29 -0400 Keith Worthington [EMAIL PROTECTED] wrote: Frank, A couple of things I wish I had been told when I started asking how to configure a new machine. Use RAID 10 (striping across mirrored disks) or RAID 0+1 (mirror a striped array) for your data. Use RAID 1 (mirror) for your OS Use RAID 1 (mirror) for the WAL. Don't put anything else on the array holding the WAL. There have been problems with Xeon processors. I believe all of these issues are covered in the article, but obviously not clearly enough. I'll work on rewording that section. - Frank Wiles [EMAIL PROTECTED] http://www.wiles.org - ---(end of broadcast)--- TIP 7: don't forget to increase your free space map settings
Re: [PERFORM] Performance Tuning Article
Dave Cramer wrote: My understanding is that it isn't particularly XEON processors that is the problem Any dual processor will exhibit the problem, XEON's with hyperthreading exacerbate the problem though and the good news is that it has been fixed in 8.1 Where's that ? The only information I have is a message from Tom Lane saying the buffer manager (or something like that) locking has been redone for 8.0. Any pointers ? Dave Thanks, -- Radu-Adrian Popescu CSA, DBA, Developer Aldrapay MD Aldratech Ltd. +40213212243 smime.p7s Description: S/MIME Cryptographic Signature
Re: [PERFORM] Performance Tuning Article
On Wed, Jun 22, 2005 at 10:31:29PM -0400, Keith Worthington wrote: Use RAID 10 (striping across mirrored disks) or RAID 0+1 (mirror a striped array) for your data. yikes! never tell an unsuspecting person to use mirred stripes--that configuration has lower reliability and performance than striped mirrors with no redeeming qualities. Mike Stone ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Performance Tuning Article
Dave Cramer [EMAIL PROTECTED] writes: AFAIK, the problem was the buffer manager The buffer manager was the place that seemed to be hit hardest by Xeon's problems with spinlock contention. I think we've partially fixed that issue in 8.1, but as we continue to improve the system's performance, it's likely to surface as a bottleneck again in other places. regards, tom lane ---(end of broadcast)--- TIP 4: Don't 'kill -9' the postmaster
Re: [PERFORM] Performance Tuning Article
Frank, I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. I believe it helps to bring together the info in a easy to digest manner. I would appreciate any feedback, comments, and especially any technical corrections. Looks nice. You should mark the link to the perf tips at Varlena.com as PostgreSQL 7.4 and augment it with the current version here: www.powerpostgresql.com/PerfList as well as the Annotated .Conf File: www.powerpostgresql.com/Docs For my part, I've generally seen that SATA disks still suck for read-write applications. I generally rate 1 UltraSCSI = 2 SATA disks for anything but a 99% read application. -- Josh Berkus Aglio Database Solutions San Francisco ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PERFORM] Performance Tuning Article
On Wed, 22 Jun 2005 10:16:03 -0700 Josh Berkus josh@agliodbs.com wrote: Frank, I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. I believe it helps to bring together the info in a easy to digest manner. I would appreciate any feedback, comments, and especially any technical corrections. Looks nice. You should mark the link to the perf tips at Varlena.com as PostgreSQL 7.4 and augment it with the current version here: www.powerpostgresql.com/PerfList as well as the Annotated .Conf File: www.powerpostgresql.com/Docs Thanks! These changes have been incorporated. For my part, I've generally seen that SATA disks still suck for read-write applications. I generally rate 1 UltraSCSI = 2 SATA disks for anything but a 99% read application. I'll work this bit of wisdom in later tonight. Thanks again for the feedback. - Frank Wiles [EMAIL PROTECTED] http://www.wiles.org - ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
Re: [PERFORM] Performance Tuning Article
On Wed, 2005-06-22 at 09:52 -0500, Frank Wiles wrote: I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. Nice work! Some minor issues I saw: * section Understanding the process, para 5: Now that PostgreSQL has a plan of what it believes to be the best way to retrieve the hardware it is time to actually get it. Do you mean retrieve the data instead of retrieve the hardware? * Perhaps some examples under Disk Configuration? * section Database Design and Layout, after new table layout: Take for example the employee table above. Your probably only display active employees throughout the majority of the application... Do you mean You're probably only displaying? HTH, -- Karim Nassar [EMAIL PROTECTED] ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PERFORM] Performance Tuning Article
[Frank Wiles - Wed at 09:52:27AM -0500] I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. I believe it helps to bring together the info in a easy to digest manner. I would appreciate any feedback, comments, and especially any technical corrections. I did not read through the whole article, but I already have some comments; work_mem was formerly sort_mem. As many of us still use pg7, you should probably have a note about it. There are already quite some short articles at the web about this issue, and that was actually my starting point when I was assigned the task of tweaking the database performance. I think diversity is a good thing, some of the short articles was relatively outdated, others were not very well written. And also - I still never had the chance to do proper benchmarking of the impact of my changes in the configuration file, I just chose to trust some of the advices when I saw almost the same advice repeated in several articles. I think we need some comprehensive chapter about this in the manual, with plenty of pointers - or eventually some separate well-organized pages telling about all known issues. It seems to me that many of the standard tips here are repeating themselves over and over again. -- Tobias Brox, +86-13521622905 Nordicbet, IT dept ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Performance Tuning Article
I've put together a short article and posted it online regarding performance tuning PostgreSQL in general. I believe it helps to bring together the info in a easy to digest manner. I would appreciate any feedback, comments, and especially any technical corrections. Looks nice. You should mark the link to the perf tips at Varlena.com as PostgreSQL 7.4 and augment it with the current version here: www.powerpostgresql.com/PerfList as well as the Annotated .Conf File: www.powerpostgresql.com/Docs Thanks! These changes have been incorporated. For my part, I've generally seen that SATA disks still suck for read-write applications. I generally rate 1 UltraSCSI = 2 SATA disks for anything but a 99% read application. I'll work this bit of wisdom in later tonight. Thanks again for the feedback. - Frank Wiles [EMAIL PROTECTED] http://www.wiles.org - Frank, A couple of things I wish I had been told when I started asking how to configure a new machine. Use RAID 10 (striping across mirrored disks) or RAID 0+1 (mirror a striped array) for your data. Use RAID 1 (mirror) for your OS Use RAID 1 (mirror) for the WAL. Don't put anything else on the array holding the WAL. There have been problems with Xeon processors. -- Kind Regards, Keith ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PERFORM] Performance Tuning
Chris Kratz wrote: Hello All, In contrast to what we hear from most others on this list, we find our database servers are mostly CPU bound. We are wondering if this is because we have postgres configured incorrectly in some way, or if we really need more powerfull processor(s) to gain more performance from postgres. If everything is cached in ram, it's pretty easy to be CPU bound. You very easily could be at this point if your database is only 2.6G and you don't touch all the tables often. I do believe that when CPU bound, the best thing to do is get faster CPUs. ... Our question is simply this, is it better to invest in a faster processor at this point, or are there configuration changes to make it faster? I've done some testing with with 4x SCSI 10k and the performance didn't improve, in fact it actually was slower the the sata drives marginally. One of our developers is suggesting we should compile postgres from scratch for this particular processor, and we may try that. Any other ideas? -Chris On this particular development server, we have: Athlon XP,3000 1.5G Mem 4x Sata drives in Raid 0 I'm very surprised you are doing RAID 0. You realize that if 1 drive goes out, your entire array is toast, right? I would recommend doing either RAID 10 (0+1), or even Raid 5 if you don't do a lot of writes. Probably most important, though is to look at the individual queries and see what they are doing. Postgresql 7.4.5 installed via RPM running on Linux kernel 2.6.8.1 Items changed in the postgresql.conf: tcpip_socket = true max_connections = 32 port = 5432 shared_buffers = 12288 # min 16, at least max_connections*2, 8KB each sort_mem=16384 vacuum_mem = 32768 # min 1024, size in KB max_fsm_pages = 6 # min max_fsm_relations*16, 6 bytes each max_fsm_relations = 1000# min 100, ~50 bytes each effective_cache_size = 115200 # typically 8KB each random_page_cost = 1# units are one sequential page fetch cost Most of these seem okay to me, but random page cost is *way* too low. This should never be tuned below 2. I think this says an index scan of *all* rows is as cheap as a sequential scan of all rows. and that should never be true. What could actually be happening is that you are getting index scans when a sequential scan would be faster. I don't know what you would see, but what does explain analyze select count(*) from blah; say. If it is an index scan, you have your machine mistuned. select count(*) always grabs every row, and this is always cheaper with a sequential scan. John =:- signature.asc Description: OpenPGP digital signature
Re: [PERFORM] Performance Tuning
On Wednesday 09 February 2005 03:38 pm, John Arbash Meinel wrote: ... I'm very surprised you are doing RAID 0. You realize that if 1 drive goes out, your entire array is toast, right? I would recommend doing either RAID 10 (0+1), or even Raid 5 if you don't do a lot of writes. grin Yeah, we know. This is a development server and we drop and reload databases regularly (sometimes several times a day). In this case we don't really care about the integrity of the data since it's for our developers to test code against. Also, the system is on a mirrored set of drives. On our live servers we have hardware raid 1 at this point for the data drives. When I/O becomes a bottleneck, we are planning on moving to Raid 10 for the data and Raid 1 for the transaction log with as many drives as I can twist arms for. Up to this point it has been easier just to stuff the servers full of memory and let the OS cache the db in memory. We know that at some point this will no longer work, but for now it is. As a side note, I learned something very interesting for our developers here. We had been doing a drop database and then a reload off a db dump from our live server for test data. This takes 8-15 minutes depending on the server (the one above takes about 8 minutes). I learned through testing that I can use create database template some_other_database and make a duplicate in about 2.5 minutes. which is a huge gain for us. We can load a pristine copy, make a duplicate, do our testing on the duplicate, drop the duplicate and create a new duplicate in less then five mintes. Cool. Probably most important, though is to look at the individual queries and see what they are doing. Postgresql 7.4.5 installed via RPM running on Linux kernel 2.6.8.1 Items changed in the postgresql.conf: tcpip_socket = true max_connections = 32 port = 5432 shared_buffers = 12288 # min 16, at least max_connections*2, 8KB each sort_mem=16384 vacuum_mem = 32768 # min 1024, size in KB max_fsm_pages = 6# min max_fsm_relations*16, 6 bytes each max_fsm_relations = 1000 # min 100, ~50 bytes each effective_cache_size = 115200# typically 8KB each random_page_cost = 1 # units are one sequential page fetch cost Most of these seem okay to me, but random page cost is *way* too low. This should never be tuned below 2. I think this says an index scan of *all* rows is as cheap as a sequential scan of all rows. and that should never be true. You caught me. I actually tweaked that today after finding a page that suggested doing that if the data was mostly in memory. I have been running it at 2, and since we didn't notice any improvement, it will be going back to 2. What could actually be happening is that you are getting index scans when a sequential scan would be faster. I don't know what you would see, but what does explain analyze select count(*) from blah; say. If it is an index scan, you have your machine mistuned. select count(*) always grabs every row, and this is always cheaper with a sequential scan. John =:- With a random_page_cost set to 1, on a larger table a select count(*) nets this... QUERY PLAN -- Aggregate (cost=9848.12..9848.12 rows=1 width=0) (actual time=4916.869..4916.872 rows=1 loops=1) - Seq Scan on answer (cost=0.00..8561.29 rows=514729 width=0) (actual time=0.011..2624.202 rows=514729 loops=1) Total runtime: 4916.942 ms (3 rows) Now here is a very curious thing. If I turn on timing and run the count without explain analyze, I get... count 514729 (1 row) Time: 441.539 ms How odd. Running the explain adds 4.5s to it. Running the explain again goes back to almost 5s. Now I wonder why that would be different. Changing random cpu cost back to 2 nets little difference (4991.940ms for explain and 496ms) But we will leave it at that for now. -- Chris Kratz Systems Analyst/Programmer VistaShare LLC www.vistashare.com ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Performance Tuning
On Wednesday 09 February 2005 03:59 pm, Greg Stark wrote: Chris Kratz [EMAIL PROTECTED] writes: We continue to tune our individual queries where we can, but it seems we still are waiting on the db a lot in our app. When we run most queries, top shows the postmaster running at 90%+ constantly during the duration of the request. The disks get touched occasionally, but not often. Our database on disk is around 2.6G and most of the working set remains cached in memory, hence the few disk accesses. All this seems to point to the need for faster processors. I would suggest looking at the top few queries that are taking the most cumulative time on the processor. It sounds like the queries are doing a ton of logical i/o on data that's cached in RAM. A few indexes might cut down on the memory bandwidth needed to churn through all that data. Hmmm, yes we continue to use indexes judiciously. I actually think we've overdone it in some cases since inserts are starting to slow in some critical areas. Items changed in the postgresql.conf: ... random_page_cost = 1# units are one sequential page fetch cost This makes it nigh impossible for the server from ever making a sequential scan when an index would suffice. What query made you do this? What plan did it fix? Yes, it got set back to 2. I was testing various settings suggested by a posting in the archives and that one didn't get reset. ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] Performance Tuning
On Wednesday 09 February 2005 05:08 pm, Merlin Moncure wrote: Hello All, In contrast to what we hear from most others on this list, we find our database servers are mostly CPU bound. We are wondering if this is because we have postgres configured incorrectly in some way, or if we really need more powerfull processor(s) to gain more performance from postgres. Yes, many apps are not I/O bound (mine isn't). Here are factors that are likely to make your app CPU bound: 1. Your cache hit ratio is very high 2. You have a lot of concurrency. 3. Your queries are complex, for example, doing sorting or statistics analysis For now, it's number 3. Relatively low usage, but very complex sql. 4. Your queries are simple, but the server has to process a lot of them (transaction overhead becomes significant) sequentially. 5. You have context switching problems, etc. On the query side, you can tune things down considerably...try and keep sorting down to a minimum (order on keys, avoid distinct where possible, use 'union all', not 'union'). Basically, reduce individual query time. Other stuff: For complex queries, use views to cut out plan generation. For simple but frequently run queries (select a,b,c from t where k), use parameterized prepared statements for a 50% cpu savings, this may not be an option in some client interfaces. Prepared statements are not something we've tried yet. Perhaps we should look into that in cases where it makes sense. On the hardware side, you will get improvements by moving to Opteron, etc. Merlin Well, that's what we were looking for. --- It sounds like our configuration as it stands is probably about as good as we are going to get with the hardware we have at this point. We are cpu bound reflecting the fact that we tend to have complex statements doing aggregates, sorts and group bys. The solutions appear to primarily be: 1. Going to faster hardware of which probably Opterons would be about the only choice. And even that probably won't be a huge difference. 2. Moving to more materialized views and prepared statements where we can. 3. Continue to tweak the sql behind our app. ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PERFORM] Performance Tuning
As a side note, I learned something very interesting for our developers here. We had been doing a drop database and then a reload off a db dump from our live server for test data. This takes 8-15 minutes depending on the server (the one above takes about 8 minutes). I learned through testing that I can use create database template some_other_database and make a duplicate in about 2.5 minutes. which is a huge gain for us. We can load a pristine copy, make a duplicate, do our testing on the duplicate, drop the duplicate and create a new duplicate in less then five mintes. I think thats because postgres just makes a file copy from the template. Thus you could make it 2x faster if you put the template in another tablespace on another drive. ---(end of broadcast)--- TIP 8: explain analyze is your friend
Re: [PERFORM] Performance Tuning
On Wed, 9 Feb 2005 17:30:41 -0500, Chris Kratz [EMAIL PROTECTED] wrote: The solutions appear to primarily be: 1. Going to faster hardware of which probably Opterons would be about the only choice. And even that probably won't be a huge difference. I'd beg to differ on that last part. The difference between a 3.6GHz Xeon and a 2.8GHz Opteron is ~150% speed increase on the Opteron on my CPU bound app. This is because the memory bandwidth on the Opteron is ENORMOUS compared to on the Xeon. Add to that the fact that you actually get to use more than about 2G of RAM directly and you've got the perfect platform for a high speed database on a budget. 2. Moving to more materialized views and prepared statements where we can. Definitely worth investigating. I wish I could, but I can't get my customers to even consider slightly out of date stats :( 3. Continue to tweak the sql behind our app. Short of an Opteron based system, this is by far your best bet. -- Mike Rylander [EMAIL PROTECTED] GPLS -- PINES Development Database Developer http://open-ils.org ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send unregister YourEmailAddressHere to [EMAIL PROTECTED])
Re: [PERFORM] Performance Tuning
The world rejoiced as [EMAIL PROTECTED] (PFC) wrote: As a side note, I learned something very interesting for our developers here. We had been doing a drop database and then a reload off a db dump from our live server for test data. This takes 8-15 minutes depending on the server (the one above takes about 8 minutes). I learned through testing that I can use create database template some_other_database and make a duplicate in about 2.5 minutes. which is a huge gain for us. We can load a pristine copy, make a duplicate, do our testing on the duplicate, drop the duplicate and create a new duplicate in less then five mintes. I think thats because postgres just makes a file copy from the template. Thus you could make it 2x faster if you put the template in another tablespace on another drive. I had some small amusement today trying this feature out in one of our environments today... We needed to make a copy of one of the databases we're replicating for the sysadmins to use for some testing. I figured using the template capability was: a) Usefully educational to one of the other DBAs, and b) Probably a quick way to copy the data over. We shortly discovered that we had to shut off the Slony-I daemon in order to get exclusive access to the database; no _big_ deal. At that point, he hit ENTER, and rather quickly saw... CREATE DATABASE. We then discovered that the sysadmins wanted the test DB to be on one of the other servers. Oops. Oh, well, we'll have to do this on the other server; no big deal. Entertainment ensued... My, that's taking a while... At about the point that we started thinking there might be a problem... CREATE DATABASE The entertainment was that the first box is one of those spiffy new 4-way Opteron boxes, whilst the slow one was a 4-way Xeon... Boy, those Opterons are faster... -- output = reverse(moc.liamg @ enworbbc) http://cbbrowne.com/info/rdbms.html No matter how far you have gone on the wrong road, turn back. -- Turkish proverb ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PERFORM] Performance Tuning
On Wed, 2005-02-09 at 15:01 -0500, Chris Kratz wrote: Hello All, In contrast to what we hear from most others on this list, we find our database servers are mostly CPU bound. We are wondering if this is because we have postgres configured incorrectly in some way, or if we really need more powerfull processor(s) to gain more performance from postgres. Not necessarily. I had a very disk bound system, bought a bunch of higher end equipment (which focuses on IO) and now have a (faster) but CPU bound system. It's just the way the cookie crumbles. Some things to watch for are large calculations which are easy to move client side, such as queries that sort for display purposes. Or data types which aren't really required (using numeric where an integer would do). We continue to tune our individual queries where we can, but it seems we still are waiting on the db a lot in our app. When we run most queries, top shows the postmaster running at 90%+ constantly during the duration of the request. Is this for the duration of a single request or 90% constantly? If it's a single request, odds are you're going through much more information than you need to. Lots of aggregate work (max / min) perhaps or count(*)'s where an approximation would do? Our question is simply this, is it better to invest in a faster processor at this point, or are there configuration changes to make it faster? I've done If it's for a single request, you cannot get single processors which are much faster than what you describe as having. Want to send us a few EXPLAIN ANALYZE's of your longer running queries? -- Rod Taylor [EMAIL PROTECTED] ---(end of broadcast)--- TIP 4: Don't 'kill -9' the postmaster
