Robert Haas escribió:
> On Wed, Nov 6, 2013 at 9:40 AM, Alvaro Herrera <alvhe...@2ndquadrant.com>
> wrote:
> > Noah Misch wrote:
> >> Incomplete list:
> >>
> >> - If smgrDoPendingDeletes() finds files to delete, mdunlink() and its
> >> callee
> >> relpathbackend() call palloc(); this is true in all supported branches.
> >> In
> >> 9.3, due to commit 279628a0, smgrDoPendingDeletes() itself calls
> >> palloc().
> >> (In fact, it does so even when the pending list is empty -- this is the
> >> only
> >> palloc() during a trivial transaction commit.) palloc() failure there
> >> yields a PANIC during commit.
> >
> > I think we should fix this routine to avoid the palloc when not necessary.
> > That initial palloc is pointless.
Here's a trivial patch we could apply to 9.3 immediately. Anything else
such as the ideas proposed below would require more effort than anyone
can probably spend here soon.
> > Also, there have been previous discussions about having relpathbackend
> > not use palloc at all. That was only because we wanted to use it in
> > pg_xlogdump which didn't have palloc support at the time, so it's no
> > longer as pressing; but perhaps it's still worthy of consideration.
>
> +1, but I'd like it better if we could find a way of avoiding the
> palloc in all cases. Panicking because we run out of memory at the
> wrong time isn't really very nice. Maybe the information needs to be
> maintained in the format in which it ultimately needs to be returned,
> so that we needn't rejigger it in the middle of a critical section.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
*** a/src/backend/catalog/storage.c
--- b/src/backend/catalog/storage.c
***************
*** 314,321 **** smgrDoPendingDeletes(bool isCommit)
PendingRelDelete *next;
int nrels = 0,
i = 0,
! maxrels = 8;
! SMgrRelation *srels = palloc(maxrels * sizeof(SMgrRelation));
prev = NULL;
for (pending = pendingDeletes; pending != NULL; pending = next)
--- 314,321 ----
PendingRelDelete *next;
int nrels = 0,
i = 0,
! maxrels = 0;
! SMgrRelation *srels = NULL;
prev = NULL;
for (pending = pendingDeletes; pending != NULL; pending = next)
***************
*** 340,347 **** smgrDoPendingDeletes(bool isCommit)
srel = smgropen(pending->relnode, pending->backend);
! /* extend the array if needed (double the size) */
! if (maxrels <= nrels)
{
maxrels *= 2;
srels = repalloc(srels, sizeof(SMgrRelation) * maxrels);
--- 340,352 ----
srel = smgropen(pending->relnode, pending->backend);
! /* allocate the initial array, or extend it, if needed */
! if (maxrels == 0)
! {
! maxrels = 8;
! srels = palloc(sizeof(SMgrRelation) * maxrels );
! }
! else if (maxrels <= nrels)
{
maxrels *= 2;
srels = repalloc(srels, sizeof(SMgrRelation) * maxrels);
***************
*** 361,370 **** smgrDoPendingDeletes(bool isCommit)
for (i = 0; i < nrels; i++)
smgrclose(srels[i]);
- }
-
- pfree(srels);
}
/*
--- 366,374 ----
for (i = 0; i < nrels; i++)
smgrclose(srels[i]);
+ pfree(srels);
+ }
}
/*
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