[HACKERS] Implementing a join algorithm in Postgres
Hi, I have written a C program which reads from 3 files(Each file is table having 2 columns and thousands of rows).The program is used to join those 3 tables and the algorithm which I have written will work only for those 3 files. Now I want to test this program for postgres. Can someone tell me how to do that, where should I include this program so that I can successfully implement that program in postgres. Thank you. -- Regards, K.Ravikiran ᐧ
Re: [HACKERS] enabling nestedloop and disabling hashjon
I am sorry for the late reply, when I disabled the hash join command enable_hashjoin=off in the postgresql.conf file, it was not working. But I when I used the command set enable_hashjoin=off command in the back end. It worked. I am not able to understand why it did not get disabled when I changed it in the postgresql file. ᐧ On Fri, Feb 13, 2015 at 2:34 AM, Jim Nasby jim.na...@bluetreble.com wrote: On 2/10/15 9:29 AM, Tom Lane wrote: Ravi Kiran ravi.kolanp...@gmail.com writes: yes sir, I did try the pg_ctl reload command, but its still using the hash join algorithm and not the nested loop algorithm. I even restarted the server, even then its still using the hash join algorithm Does show enable_hashjoin say it's off? If not, I think you must've fat-fingered the postgresql.conf change somehow. For future reference, posts like this belong on pgsql-performance. The other possibility is that the query estimates are so high that the setting doesn't matter. When you set any of the enable_* settings to off, all that really happens is the planner adds a cost of 10M to those nodes when it's planning. Normally that's enough to toss those plans out, but in extreme cases the cost estimates will still come up with the un-desired plan. Can you post EXPLAIN ANALYZE output with the setting on and off? Or at least plain EXLPAIN output. -- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com
Re: [HACKERS] enabling nestedloop and disabling hashjon
sorry for the inconvenience if caused to anyone, but as David G johnston said, I was trying to change how the postgresql works and was not able to figure out how it should be done. I will make sure it will be clear from the next time. Thank you very much. @Tom lane Sir, I forgot to remove the # comment marker in the file's entry, Thank you. ᐧ On Fri, Feb 13, 2015 at 2:50 AM, David G Johnston david.g.johns...@gmail.com wrote: Jim Nasby-5 wrote On 2/10/15 9:29 AM, Tom Lane wrote: Ravi Kiran lt; ravi.kolanpaka@ gt; writes: yes sir, I did try the pg_ctl reload command, but its still using the hash join algorithm and not the nested loop algorithm. I even restarted the server, even then its still using the hash join algorithm Does show enable_hashjoin say it's off? If not, I think you must've fat-fingered the postgresql.conf change somehow. For future reference, posts like this belong on pgsql-performance. but postgres is still using the hash join algorithm even after modifying the postgresql code To be fair given the original post, and some other recent posts by the same author, the question is not why is my query performing slowly but rather I'm trying to change how PostgreSQL works and cannot figure out how to properly enable and disable algorithms. -hackers seems like the proper forum though the OP could give more context as to his overarching goals to make that more clear to readers. David J. -- View this message in context: http://postgresql.nabble.com/enabling-nestedloop-and-disabling-hashjon-tp5837275p5837728.html Sent from the PostgreSQL - hackers mailing list archive at Nabble.com. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] enabling nestedloop and disabling hashjon
yes sir, I did try the pg_ctl reload command, but its still using the hash join algorithm and not the nested loop algorithm. I even restarted the server, even then its still using the hash join algorithm Thanks ᐧ On Tue, Feb 10, 2015 at 5:28 AM, Tom Lane t...@sss.pgh.pa.us wrote: Ravi Kiran ravi.kolanp...@gmail.com writes: I tried modifying the postgresql.conf file where I set the value enable_hashjoin=off and also enable_mergejoin=off, so that I could force postgres to use nested loop. but postgres is still using the hash join algorithm even after modifying the postgresql code. Did you remember pg_ctl reload? enable_hashjoin=off will most certainly work if it's active. regards, tom lane
[HACKERS] enabling nestedloop and disabling hashjon
Hi, I want to disable the hashjoin algorithm used by postgres by default, and enable the nested loop join algorithm, can some one tell me how to do that. I tried modifying the postgresql.conf file where I set the value enable_hashjoin=off and also enable_mergejoin=off, so that I could force postgres to use nested loop. but postgres is still using the hash join algorithm even after modifying the postgresql code. can some one tell me what I am doing wrong, or is there any other file where I need to modify to enable nested loop join algorithm. Thanks ᐧ
[HACKERS] Hash Function
Hi, I want to know what kind of hash function postgres is using currently, can someone please explain the algorithm postgres is using for the hash function in the hash join algorithm. Thanks, K.Ravikiran
[HACKERS] NODE
hi, I am going through the hashjoin algorithm in postgres. I find a function ExecHashjoin , which is called each time a new tuple is required by the hash join *Node.* could someone explain what exactly node mean in postgres. Thanks
[HACKERS] attaching a process in eclipse
hi, I am working with postgresql 9.4.0 source using eclipse(indigo version) in ubuntu 14.04. I am facing a problem of attaching a client process to postgresql server. I am following the steps given in this link https://wiki.postgresql.org/wiki/Working_with_Eclipse#Debugging_PostgreSQL_from_Eclipse In the debug configuration , I have given the following information in the fields. C/C++ Application :- src/backend/postgres Project :- postgresql-9.4.0 I have found out the process id of the client process using select pg_backend_pid() and used it to attach the server. But I am getting the following error whenever I do this Could not attach to process. If your uid matches the uid of the target process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try again as the root user. For more details, see /etc/sysctl.d/10-ptrace.conf how do we rectify this error? Thank you Regards K.Ravikiran
Re: [HACKERS] attaching a process in eclipse
Sir, I followed the instructions in the link which you gave , but this time I am getting the following error. *Can't find a source file at /build/buildd/eglibc-2.19/socket/../sysdeps/unix/sysv/linux/x86_64/recv.c * *Locate the file or edit the source lookup path to include its location.* is the error something related my OS or is it related to postgres. Thank you for telling the mistake, I will follow the things which you told from the next time. Thank you On Sun, Dec 28, 2014 at 7:36 PM, Craig Ringer cr...@2ndquadrant.com wrote: On 12/28/2014 07:49 PM, Ravi Kiran wrote: Thank you for the response sir, I am running both the eclipse and the client under the same user name which is ravi, I have installed postgres source code under the user ravi not postgres, It doesn't matter how you installed it. How you *run* it matters. If the postgresql processes run as user 'ravi' and so does Eclipse, then your problem is the one in the article I already sent you a link to, and you should follow those instructions. should I change it and work under postgres No. If you read my explanation you would understand that this would just make it worse, because you can't attach to a process under a different user id. and for that to happen should I uninstall the whole postgres and re install under the new user postgres. That won't help. By the way, it looks like you also posted this to Stack Overflow: http://stackoverflow.com/q/27676836/398670 It's OK to do that, but *please mention you posted somewhere else too* or preferably link to the relevant article in the mailing list archives. Also, when replying to mail on a list, please reply-to-all. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training Services
[HACKERS] mysql with postgres
hi all, Is postgres source code compatible with mysql database?? If it is, could someone could give me some links so that I can do that. I want to hack into the postgres source code, but as I am comfortable with mysql, I want to use the mysql database not postgres. any references would be fine. thank you
[HACKERS] debugging with child process
hi, can any one help me with the 4th and 5th steps of the following link which is to debug with a child process in postgres. *https://wiki.postgresql.org/wiki/Working_with_Eclipse#Debugging_with_child_processes https://wiki.postgresql.org/wiki/Working_with_Eclipse#Debugging_with_child_processes* when I give the following fields in the debug configuration *c/c++ Application : postgres* *Project - psql* *Build Configuration - Use Active* I am getting the following error- * No source available for __kernel_vsyscall() at 0xb726a424 * Is there any better tool other than eclipse to use for editing or knowing about source code in postgres. Thank you
