No need to wait for idle-in-transaction sessions during index builds.
GetCurrentVirtualXIDs() specifically *includes* backends that have
proc->xmin == InvalidTransactionId (0), but I'm not sure why.
$SUBJECT is currently used by DefineIndex() to wait for all backends
that might be able to see index changes in phase 2 of concurrent index
build. The code comments say "we have to wait out any transactions that
might have older snapshots". If proc->xmin == 0 it is because they
haven't got any snapshots at all and therefore the index build does
*not* need to wait for them.
I'm using this routine for Hot Standby also, so patching this will allow
me to ignore idle-in-transaction sessions unless they are from
serializable transactions or have open cursors. But there's no need for
me to include this in the patch if its a general fix.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
Index: src/backend/storage/ipc/procarray.c
===================================================================
RCS file: /home/sriggs/pg/REPOSITORY/pgsql/src/backend/storage/ipc/procarray.c,v
retrieving revision 1.47
diff -c -r1.47 procarray.c
*** src/backend/storage/ipc/procarray.c 1 Jan 2009 17:23:47 -0000 1.47
--- src/backend/storage/ipc/procarray.c 16 Jan 2009 16:39:23 -0000
***************
*** 1023,1030 ****
*
* The array is palloc'd and is terminated with an invalid VXID.
*
! * If limitXmin is not InvalidTransactionId, we skip any backends
! * with xmin >= limitXmin. If allDbs is false, we skip backends attached
* to other databases. If excludeVacuum isn't zero, we skip processes for
* which (excludeVacuum & vacuumFlags) is not zero. Also, our own process
* is always skipped.
--- 1023,1030 ----
*
* The array is palloc'd and is terminated with an invalid VXID.
*
! * If limitXmin is not InvalidTransactionId, we skip any backends with a
! * valid xmin >= limitXmin. If allDbs is false, we skip backends attached
* to other databases. If excludeVacuum isn't zero, we skip processes for
* which (excludeVacuum & vacuumFlags) is not zero. Also, our own process
* is always skipped.
***************
*** 1059,1069 ****
TransactionId pxmin = proc->xmin;
/*
! * Note that InvalidTransactionId precedes all other XIDs, so a
! * proc that hasn't set xmin yet will always be included.
*/
if (!TransactionIdIsValid(limitXmin) ||
! TransactionIdPrecedes(pxmin, limitXmin))
{
VirtualTransactionId vxid;
--- 1059,1070 ----
TransactionId pxmin = proc->xmin;
/*
! * If we have a specific limitXmin then we need not include
! * any procs with an unset xmin, since they have no snapshots
! * older than limitXmin
*/
if (!TransactionIdIsValid(limitXmin) ||
! (TransactionIdIsValid(pxmin) && TransactionIdPrecedes(pxmin, limitXmin)))
{
VirtualTransactionId vxid;
--
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