Vivekanand Joshi <vjoshi@xxxxxxxxxxxxxxxxxxx> writes: > 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? Consider just disabling that setting for 1 or a few odd queries you have for which they are known to plan badly. begin; set local enable_nestloops to false; select ...; commit/abort; I'd say never make that sort of setting DB or cluster-wide. > > > 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 -- Jerry Sievers Postgres DBA/Development Consulting e: postgres.consulting@xxxxxxxxxxx p: 312.241.7800 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
