Re: [PERFORM] FW: performance issue with a 2.5gb joinded table
Daniel, Somehow oracle seems to know that a right join is the better way to go. In fact, PostgreSQL is just doing the same thing: it hashes smaller table and scans the bigger one. Could you please clarify how do you consume 25M rows? It could be the difference of response times comes not from the PostgreSQL itself, but from the client code. Could you please add the following information? 1) Execution time of simple query that selects MAX of all the required columns select max(test1.slsales_batch) , max(test1.slsales_checksum), I mean not explain (analyze, buffers), but simple execution. The purpose of MAX is to split overhead of consuming of the resultset from the overhead of producing it. 2) explain (analyze, buffers) for the same query with maxes. That should reveal the overhead of explain analyze itself. 3) The output of the following SQLPlus script (from Oracle): set linesize 1000 pagesize 1 trimout on trimspool on time on timing on spool slow_query.lst select /*+ gather_plan_statistics */ max(test1.slsales_batch) , max(test1.slsales_checksum), ..; select * from table(dbms_xplan.display_cursor(null, null, 'ALLSTATS LAST')); spool off That would display detailed statistics on execution time similar to the explain (analyze, buffers). 4) Could you please clarify how did you migrate test1 table? I guess the order of rows in that table might affect overall execution time. Sorted table would be more CPU cache friendly, thus giving speedup. (see [1] for similar example). As far as I understand, simple create table as select * from test1 order by slsales_date_id, slsales_prod_id should improve cache locality. [1]: http://stackoverflow.com/questions/11227809/why-is-processing-a-sorted-array-faster-than-an-unsorted-array -- Regards, Vladimir Sitnikov
Re: [PERFORM] FW: performance issue with a 2.5gb joinded table
Heikki Linnakangas hlinnakan...@vmware.com writes: One difference is that numerics are stored more tightly packed on Oracle. Which is particularly good for Oracle as they don't have other numeric data types than number. On PostgreSQL, you'll want to use int4 for ID-fields, where possible. An int4 always takes up 4 bytes, while a numeric holding an integer value in the same range is typically 5-9 bytes. Replacing those numeric(8) and numeric(16) fields with int4 and int8 would be greatly beneficial to comparison and hashing performance, not just table size. I'm a bit surprised that EDB's porting tools evidently don't do this automatically (I infer from the reference to PPAS that the OP is using EDB ...) regards, tom lane -- 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] FW: performance issue with a 2.5gb joinded table
-Original Message- From: Tom Lane [mailto:t...@sss.pgh.pa.us] Sent: Freitag, 4. Januar 2013 21:41 To: Heikki Linnakangas Cc: Daniel Westermann; 'pgsql-performance@postgresql.org' Subject: Re: [PERFORM] FW: performance issue with a 2.5gb joinded table Heikki Linnakangas hlinnakan...@vmware.com writes: One difference is that numerics are stored more tightly packed on Oracle. Which is particularly good for Oracle as they don't have other numeric data types than number. On PostgreSQL, you'll want to use int4 for ID-fields, where possible. An int4 always takes up 4 bytes, while a numeric holding an integer value in the same range is typically 5-9 bytes. Replacing those numeric(8) and numeric(16) fields with int4 and int8 would be greatly beneficial to comparison and hashing performance, not just table size. I'm a bit surprised that EDB's porting tools evidently don't do this automatically (I infer from the reference to PPAS that the OP is using EDB ...) regards, tom lane Thanks, tom. Any clue where there remaining around 500mb difference come from ? converted all the numeric(8) to int and this saved around 380mb of storage and around 10 secs exectution time... both databases have their files on standard ext3, same fs options. Given that the table has around 25'000'000 rows this is still approx. 20 bytes more per row on average Regards Daniel -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
[PERFORM] FW: performance issue with a 2.5gb joinded table
Hi Listers, we migrated an oracle datawarehouse to postgresql 9.1 ( ppas 9.1.7.12 ) and are facing massive issues with response times in postgres when compared to the oracle system. Both database run on the same hardware and storage ( rhel5.8 64bit ). Oracle memory parameters are: SGA=1gb PGA=200mb Postgres currently runs with 15gb of shared buffers ( that’s because the big table in question is around 2.5gb in size and one suggestion was to increase that much so postgresql will cache the complete table. and this is the case now ). explain (analyze,buffers) SELECT test1.slsales_batch , test1.slsales_checksum , test1.slsales_reg_id , test1.slsales_prod_id , test1.slsales_date_id , test1.slsales_pos_id , test1.slsales_amt_sales_gross , test1.slsales_amt_sales_discount , test1.slsales_units_sales_gross , test1.slsales_amt_returns , test1.slsales_amt_returns_discount , test1.slsales_units_returns , (test1.slsales_amt_sales_gross - test1.slsales_amt_returns) * mgmt_fact_winratio.winratio_ratio AS slsales_amt_est_winnings , mgmt_fact_winratio.winratio_ratio AS slsales_ratio FROM mgmtt_own.test1 LEFT JOIN mgmtt_own.mgmt_fact_winratio ON mgmt_fact_winratio.winratio_date_id = test1.slsales_date_id Oracle’s explain plan looks like this: | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | | 0 | SELECT STATEMENT ||25M| 1527M| | 115K (3)| 00:23:10 | |* 1 | HASH JOIN RIGHT OUTER||25M| 1527M| 4376K| 115K (3)| 00:23:10 | | 2 | TABLE ACCESS FULL | MGMT_FACT_WINRATIO | 159K| 2498K| | 167 (5)| 00:00:03 | | 3 | TABLE ACCESS FULL | TEST1 |25M| 1139M| | 43435 (5)| 00:08:42 | Predicate Information (identified by operation id): --- 1 - access(MGMT_FACT_WINRATIO.WINRATIO_PROD_ID(+)=TEST1.SLSALES_PROD_ID AND MGMT_FACT_WINRATIO.WINRATIO_DATE_ID(+)=TEST1.SLSALES_DATE_ID) Somehow oracle seems to know that a right join is the better way to go. Postgres’s explain plan: QUERY PLAN Hash Left Join (cost=3948.52..13646089.21 rows=25262160 width=61) (actual time=260.642..81240.692 rows=25262549 loops=1) Hash Cond: ((test1.slsales_date_id = mgmt_fact_winratio.winratio_date_id) AND (test1.slsales_prod_id = mgmt_fact_winratio.winratio_prod_id)) Buffers: shared hit=306590 - Seq Scan on test1 (cost=0.00..254148.75 rows=25262160 width=56) (actual time=0.009..15674.535 rows=25262161 loops=1) Buffers: shared hit=305430 - Hash (cost=1582.89..1582.89 rows=157709 width=19) (actual time=260.564..260.564 rows=157709 loops=1) Buckets: 16384 Batches: 1 Memory Usage: 7855kB Buffers: shared hit=1160 - Seq Scan on mgmt_fact_winratio (cost=0.00..1582.89 rows=157709 width=19) (actual time=0.008..114.406 rows=157709 loops=1) Buffers: shared hit=1160 Total runtime: 95762.025 ms (11 rows) Tried to modify the statement according to oracle’s plan, but this did not help: explain (analyze,buffers) SELECT test1.slsales_batch , test1.slsales_checksum , test1.slsales_reg_id , test1.slsales_prod_id , test1.slsales_date_id , test1.slsales_pos_id , test1.slsales_amt_sales_gross , test1.slsales_amt_sales_discount , test1.slsales_units_sales_gross , test1.slsales_amt_returns , test1.slsales_amt_returns_discount , test1.slsales_units_returns , (test1.slsales_amt_sales_gross - test1.slsales_amt_returns) * mgmt_fact_winratio.winratio_ratio AS slsales_amt_est_winnings , mgmt_fact_winratio.winratio_ratio AS slsales_ratio FROM mgmtt_own.test1 , mgmtt_own.mgmt_fact_winratio WHERE mgmt_fact_winratio.winratio_prod_id(+) = test1.slsales_prod_id AND mgmt_fact_winratio.winratio_date_id(+) = test1.slsales_date_id ; QUERY PLAN Hash Left Join (cost=3948.52..13646089.21 rows=25262160 width=61) (actual time=276.605..80629.400 rows=25262549 loops=1) Hash Cond: ((test1.slsales_prod_id = mgmt_fact_winratio.winratio_prod_id) AND (test1.slsales_date_id =
Re: [PERFORM] FW: performance issue with a 2.5gb joinded table
On 03.01.2013 15:30, Daniel Westermann wrote:
What additionally makes me wonder is, that the same table in oracle is taking
much less space than in postgresql:
SQL select sum(bytes) from dba_extents where segment_name = 'TEST1';
SUM(BYTES)
--
1610612736
select pg_relation_size('mgmtt_own.test1');
pg_relation_size
--
2502082560
(1 row)
(sysdba@[local]:) [bi_dwht] \d+ mgmtt_own.test1
Table mgmtt_own.test1
Column| Type | Modifiers | Storage |
Description
--+---+---+-+-
slsales_batch| numeric(8,0) | | main|
slsales_checksum | numeric(8,0) | | main|
slsales_reg_id | numeric(8,0) | | main|
slsales_prod_id | numeric(8,0) | | main|
slsales_date_id | numeric(8,0) | | main|
slsales_pos_id | numeric(8,0) | | main|
slsales_amt_sales_gross | numeric(16,6) | | main|
slsales_amt_sales_discount | numeric(16,6) | | main|
slsales_units_sales_gross| numeric(8,0) | | main|
slsales_amt_returns | numeric(16,6) | | main|
slsales_amt_returns_discount | numeric(16,6) | | main|
slsales_units_returns| numeric(8,0) | | main|
slsales_amt_est_winnings | numeric(16,6) | | main|
Indexes:
itest1 btree (slsales_date_id) CLUSTER, tablespace mgmtt_idx
itest2 btree (slsales_prod_id), tablespace mgmtt_idx
Has OIDs: no
Tablespace: mgmtt_dat
One difference is that numerics are stored more tightly packed on
Oracle. Which is particularly good for Oracle as they don't have other
numeric data types than number. On PostgreSQL, you'll want to use int4
for ID-fields, where possible. An int4 always takes up 4 bytes, while a
numeric holding an integer value in the same range is typically 5-9 bytes.
- Heikki
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Re: [PERFORM] FW: performance issue with a 2.5gb joinded table
-Original Message-
From: Heikki Linnakangas [mailto:hlinnakan...@vmware.com]
Sent: Donnerstag, 3. Januar 2013 18:02
To: Daniel Westermann
Cc: 'pgsql-performance@postgresql.org'
Subject: Re: [PERFORM] FW: performance issue with a 2.5gb joinded table
On 03.01.2013 15:30, Daniel Westermann wrote:
What additionally makes me wonder is, that the same table in oracle is taking
much less space than in postgresql:
SQL select sum(bytes) from dba_extents where segment_name =
SQL 'TEST1';
SUM(BYTES)
--
1610612736
select pg_relation_size('mgmtt_own.test1');
pg_relation_size
--
2502082560
(1 row)
(sysdba@[local]:) [bi_dwht] \d+ mgmtt_own.test1
Table mgmtt_own.test1
Column| Type | Modifiers | Storage |
Description
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
--+---+---+-+-
slsales_batch| numeric(8,0) | | main|
slsales_checksum | numeric(8,0) | | main|
slsales_reg_id | numeric(8,0) | | main|
slsales_prod_id | numeric(8,0) | | main|
slsales_date_id | numeric(8,0) | | main|
slsales_pos_id | numeric(8,0) | | main|
slsales_amt_sales_gross | numeric(16,6) | | main|
slsales_amt_sales_discount | numeric(16,6) | | main|
slsales_units_sales_gross| numeric(8,0) | | main|
slsales_amt_returns | numeric(16,6) | | main|
slsales_amt_returns_discount | numeric(16,6) | | main|
slsales_units_returns| numeric(8,0) | | main|
slsales_amt_est_winnings | numeric(16,6) | | main|
Indexes:
itest1 btree (slsales_date_id) CLUSTER, tablespace mgmtt_idx
itest2 btree (slsales_prod_id), tablespace mgmtt_idx
Has OIDs: no
Tablespace: mgmtt_dat
One difference is that numerics are stored more tightly packed on Oracle. Which
is particularly good for Oracle as they don't have other numeric data types
than number. On PostgreSQL, you'll want to use int4 for ID-fields, where
possible. An int4 always takes up 4 bytes, while a numeric holding an integer
value in the same range is typically 5-9 bytes.
- Heikki
Thanks for poiting that out, Heikki.
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