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Re: Replication Syatem

From: "Gauri Kanekar" <meetgaurikanekar(at)gmail(dot)com>
To: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
Cc: "Greg Smith" <gsmith(at)gregsmith(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Replication Syatem
Date: 2008-04-29 12:59:43
Message-ID: 7e4ba9550804290559t7948d549j7e506154c0b1ed38@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
Thanx for the help.

Need some more help.

"table1" has two indices
unique indx1 = "pkfld"
unique indx2 = "fkfld1,fkfld2"

did following steps in the listed order -

1. vacuumed the whole DB
2. "table1"
      RecCnt ==> 11970789
      Size ==> 2702.41 MB
3.update "table1" set fld7 = 1000 where fld1/1000000 = 999 ;
    this UPDATED 1230307 records
4. checked "table1" size again
     Reccnt =>   11970789
     Size ==> 2996.57MB
5. Again did the update, update "table1" set fld7 = 1000 where fld1/1000000
= 999 ;
    this UPDATED 1230307 records
6. Got "table1" size as
    RecCnt ==> 11970789
    Size ==> 3290.64
7. Updated again, update "table1" set fld7 = 1000 where fld1/1000000 = 999 ;
    this UPDATED 1230307 records
6. "table1" size as
    RecCnt ==> 11970789
    Size ==> 3584.66

Found that the size increased gradually. Is HOT working over here ??
Guide me if im doing something wrong.

~ Gauri

On Tue, Apr 29, 2008 at 4:55 PM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
wrote:

> On Tue, Apr 29, 2008 at 4:35 PM, Gauri Kanekar
> <meetgaurikanekar(at)gmail(dot)com> wrote:
>
> >
> > Do we need to do any special config changes or any other setting for HOT
> to
> > work??
>
> No. HOT is enabled by default, on all tables. There is no way and need
> to disable it.
>
> >
> > Any special guideline to follow to make HOT working??
> >
>
> You can do couple of things to benefit from HOT.
>
> 1. HOT addresses a special, but common case where UPDATE operation
> does not change any of the index keys. So check if your UPDATE changes
> any of the index keys. If so, see if you can avoid having index
> involving that column. Of course, I won't advocate dropping an index
> if it would drastically impact your frequently run queries.
>
> 2. You may leave some free space in the heap (fillfactor less than
> 100). My recommendation would be to leave space worth of one row or
> slightly more than that to let first UPDATE be an HOT update.
> Subsequent UPDATEs in the page may reuse the dead row created by
> earlier UPDATEs.
>
> 3. Avoid any long running transactions.
>
> Thanks,
> Pavan
>
> --
> Pavan Deolasee
> EnterpriseDB http://www.enterprisedb.com
>



-- 
Regards
Gauri

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