Re: PATCH to allow concurrent VACUUMs to not lock each - Mailing list pgsql-patches

Hannu Krosing wrote:
> *** src/backend/access/transam/xact.c    28 Apr 2005 21:47:10 -0000    1.200
> --- src/backend/access/transam/xact.c    17 May 2005 22:06:34 -0000
> ***************
> *** 1411,1416 ****
> --- 1411,1424 ----
>       AfterTriggerBeginXact();
>
>       /*
> +      * mark the transaction as not VACUUM  (vacuum_rel will set isVacuum to true
> +      * directly after calling BeginTransactionCommand() )
> +      */
> +     if (MyProc != NULL)
> +     {
> +         MyProc->inVacuum = false;
> +     }

I'm a little worried about having this set to "true" after a VACUUM is
executed, and only reset to false when the next transaction is begun: it
shouldn't affect correctness right now, but it seems like asking for
trouble. Resetting the flag to "false" after processing a transaction
would probably be worth doing.

> *** src/backend/commands/vacuum.c    6 May 2005 17:24:53 -0000    1.308
> --- src/backend/commands/vacuum.c    17 May 2005 22:06:35 -0000
> ***************
> *** 420,425 ****
> --- 418,428 ----
>                   if (use_own_xacts)
>                   {
>                       StartTransactionCommand();
> +                     if (MyProc != NULL)  /* is this needed here ? */
> +                     {
> +                         /* so other vacuums don't look at our xid/xmin in GetOldestXmin() */
> +                         MyProc->inVacuum = true;
> +                     }
>                       /* functions in indexes may want a snapshot set */
>                       ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
>                   }

Is it valid to apply this optimization to ANALYZE? Since ANALYZE updates
pg_statistic, ISTM it can affect tuple visibility.

> *** src/backend/storage/ipc/sinval.c    31 Dec 2004 22:00:56 -0000    1.75
> --- src/backend/storage/ipc/sinval.c    17 May 2005 22:06:36 -0000
> ***************
> *** 845,854 ****
>                * them as running anyway.    We also assume that such xacts
>                * can't compute an xmin older than ours, so they needn't be
>                * considered in computing globalxmin.
>                */
>               if (proc == MyProc ||
>                   !TransactionIdIsNormal(xid) ||
> !                 TransactionIdFollowsOrEquals(xid, xmax))
>                   continue;
>
>               if (TransactionIdPrecedes(xid, xmin))
> --- 845,858 ----
>                * them as running anyway.    We also assume that such xacts
>                * can't compute an xmin older than ours, so they needn't be
>                * considered in computing globalxmin.
> +              *
> +              * there is also no need to consider transaxtions runnibg the
> +              * vacuum command as it will not affect tuple visibility
>                */

Typos.

-Neil