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Re: possible patch to increase number of hash overflow pages?

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Stephen Ramsey <sramsey(at)internap(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-patches(at)postgresql(dot)org
Subject: Re: possible patch to increase number of hash overflow pages?
Date: 2001-06-19 23:46:02
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-patches
> It looks (from the hash algorithm code) as if the system is possibly
> needing more splitpoints than can be accomodated by the HashMetaPageData
> structure, rather than running out of overflow pages, because the error
> message that I'm getting is when the "splitnum" variable is greater than
> NCACHED, the latter being the array bound for the hashm_spares[] element
> of the HashMetaPageData structure.  From src/backend/access/hashovfl.c:
> #define OVMSG   "HASH: Out of overflow pages.  Out of luck.\n"
>         if (offset > SPLITMASK)
>         {
>                 if (++splitnum >= NCACHED)
>                         elog(ERROR, OVMSG);
>                 metap->OVFL_POINT = splitnum;
>                 metap->SPARES[splitnum] = metap->SPARES[splitnum - 1];
>                 metap->SPARES[splitnum - 1]--;
>                 offset = 0;
>         }
> So that's why I bumped the number of bits (in the OverflowPageAddress
> type) assigned to keep track of splitpoints to 8 bits.

If you want to work on the hash stuff, let us know.  We are looking for
someone to do performance testing and debugging on hash indexes.

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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