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Improve snapshot manager by keeping explicit track of snapshots.

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There are two ways to track a snapshot: there's the "registered" list, which
is used for arbitrary long-lived snapshots; and there's the "active stack",
which is used for the snapshot that is considered "active" at any time.
This also allows users of snapshots to stop worrying about snapshot memory
allocation and freeing, and about using PG_TRY blocks around ActiveSnapshot
assignment.  This is all done automatically now.

As a consequence, this allows us to reset MyProc->xmin when there are no
more snapshots registered in the current backend, reducing the impact that
long-running transactions have on VACUUM.
This commit is contained in:
Alvaro Herrera
2008-05-12 20:02:02 +00:00
parent aa82790fca
commit 5da9da71c4
27 changed files with 995 additions and 551 deletions
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7
src/backend/tcop/fastpath.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/tcop/fastpath.c,v 1.99 2008/03/26 18:48:59 alvherre Exp $
* $PostgreSQL: pgsql/src/backend/tcop/fastpath.c,v 1.100 2008/05/12 20:02:01 alvherre Exp $
*
* NOTES
* This cruft is the server side of PQfn.
@ -309,7 +309,7 @@ HandleFunctionRequest(StringInfo msgBuf)
* Now that we know we are in a valid transaction, set snapshot in case
* needed by function itself or one of the datatype I/O routines.
*/
ActiveSnapshot = CopySnapshot(GetTransactionSnapshot());
PushActiveSnapshot(GetTransactionSnapshot());
/*
* Begin parsing the buffer contents.
@ -396,6 +396,9 @@ HandleFunctionRequest(StringInfo msgBuf)
SendFunctionResult(retval, fcinfo.isnull, fip->rettype, rformat);
/* We no longer need the snapshot */
PopActiveSnapshot();
/*
* Emit duration logging if appropriate.
*/