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04-09-2008, 11:22 PM
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 postgresql is slow with larger table even it is in RAM I have a table with 32 lakh record in it. Table size is nearly 700 MB, and my machine had a 1 GB + 256 MB RAM, i had created the table space in RAM, and then created this table in this RAM. So now everything is in RAM, if i do a count(*) on this table it returns 327600 in 3 seconds, why it is taking 3 seconds ????? because am sure that no Disk I/O is happening. ( using vmstat i had confirmed, no disk I/O is happening, swap is also not used ) Any Idea on this ??? I searched a lot in newsgroups ... can't find relevant things.... ( because everywhere they are speaking about disk access speed, here i don't want to worry about disk access ) If required i will give more information on this.      |
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04-09-2008, 11:23 PM
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| Re: postgresql is slow with larger table even it is in RAM On 2008-03-25 09:51, sathiya psql wrote: > Table size is nearly 700 MB, > and my machine had a 1 GB + 256 MB RAM, i had created the table space in > RAM, and then created this table in this RAM. > > So now everything is in RAM, if i do a count(*) on this table it returns > 327600 in 3 seconds, why it is taking 3 seconds ????? PostgreSQL needs to scan the whole table. And 700MB is a lot of data even when in RAM. Check this: $ dd if=/dev/zero bs=1M count=700 | cat > /dev/null 734003200 bytes (734 MB) copied, 1.38732 s, 529 MB/s This command will just copy 700MB of zeros around in RAM, and it takes over 1s to do it on my Pentium D 3,4GHz. PostgreSQL would need to do much more with this data. Maybe you just got bitten by count(*) gotcha: http://sql-info.de/en/postgresql/pos...tchas.html#1_7 Maybe you'll get by with an estimate. Regards Tometzky -- ....although Eating Honey was a very good thing to do, there was a moment just before you began to eat it which was better than when you were... Winnie the Pooh -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general |
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04-09-2008, 11:23 PM
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| Re: postgresql is slow with larger table even it is inRAM Please stop reposting your questions to multiple groups. Since all your questions are about performance, please stick to the pgsql-performance list. Posting to pgsql-sql is not really appropriate, and in pgsql-admin you're totally off-topic. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general |
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04-09-2008, 11:23 PM
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| Re: postgresql is slow with larger table even it is in RAM ok On Tue, Mar 25, 2008 at 5:33 PM, Alvaro Herrera <alvherre@commandprompt.com> wrote: > Please stop reposting your questions to multiple groups. Since all your > questions are about performance, please stick to the pgsql-performance > list. Posting to pgsql-sql is not really appropriate, and in > pgsql-admin you're totally off-topic. > > -- > Alvaro Herrera > http://www.CommandPrompt.com/ > PostgreSQL Replication, Consulting, Custom Development, 24x7 support > |
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