So, here is the first taste of success and which gives me the confidence that if properly worked out with a good hardware and proper tuning, PostgreSQL could be a good replacement. Out of the 9 reports which needs to be migrated in PostgreSQL, 3 are now running. Report 4 was giving an issue and I will see it tomorrow. Just to inform you guys that, the thing that helped most is setting enable_nestloops to false worked. Plans are now not miscalculated. But this is not a production-suitable setting. So what do you think how to get a work around this? Regards, Vivek -----Original Message----- From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] On Behalf Of Tomas Vondra Sent: Tuesday, March 17, 2015 9:00 PM To: pgsql-performance@xxxxxxxxxxxxxx Subject: Re: Performance issues On 17.3.2015 16:24, Thomas Kellerer wrote: > Tomas Vondra schrieb am 17.03.2015 um 15:43: >> On 17.3.2015 15:19, Thomas Kellerer wrote: >>> Tomas Vondra schrieb am 17.03.2015 um 14:55: >>>> (2) using window functions, e.g. like this: >>>> >>>> SELECT * FROM ( >>>> SELECT *, >>>> ROW_NUMBER() OVER (PARTITION BY touchpoint_execution_id >>>> ORDER BY FROM max_creation_dt) AS rn >>>> FROM s_f_touchpoint_execution_status_history >>>> ) foo WHERE rn = 1 >>>> >>>> But estimating this is also rather difficult ... >>> >>> >>> From my experience rewriting something like the above using DISTINCT >>> ON is usually faster. >> >> How do you get the last record (with respect to a timestamp column) >> using a DISTINCT ON? > > You need to use "order by ... desc". See here: > http://sqlfiddle.com/#!15/d4846/2 Nice, thanks! > > Btw: your row_number() usage wouldn't return the "latest" row either. > It would return the "oldest" row. Oh, right. I forgot the DESC in the window. -- Tomas Vondra http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
