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Fix rare sharedtuplestore.c corruption.

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If the final chunk of an oversized tuple being written out to disk was
exactly 32760 bytes, it would be corrupted due to a fencepost bug.

Bug #17619.  Back-patch to 11 where the code arrived.

While testing that (see test module in archives), I (tmunro) noticed
that the per-participant page counter was not initialized to zero as it
should have been; that wasn't a live bug when it was written since DSM
memory was originally always zeroed, but since 14
min_dynamic_shared_memory might be configured and it supplies non-zeroed
memory, so that is also fixed here.

Author: Dmitry Astapov <dastapov@gmail.com>
Discussion: https://postgr.es/m/17619-0de62ceda812b8b5%40postgresql.org
This commit is contained in:
Thomas Munro 2023-01-26 14:50:07 +13:00
parent e9774151c2
commit 2f65b84683
1 changed files with 3 additions and 2 deletions
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5
src/backend/utils/sort/sharedtuplestore.c
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@ -158,6 +158,7 @@ sts_initialize(SharedTuplestore *sts, int participants,
LWLockInitialize(&sts->participants[i].lock, LWLockInitialize(&sts->participants[i].lock,
LWTRANCHE_SHARED_TUPLESTORE); LWTRANCHE_SHARED_TUPLESTORE);
sts->participants[i].read_page = 0; sts->participants[i].read_page = 0;
sts->participants[i].npages = 0;
sts->participants[i].writing = false; sts->participants[i].writing = false;
} }
@ -319,7 +320,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
/* Do we have space? */ /* Do we have space? */
size = accessor->sts->meta_data_size + tuple->t_len; size = accessor->sts->meta_data_size + tuple->t_len;
if (accessor->write_pointer + size >= accessor->write_end) if (accessor->write_pointer + size > accessor->write_end)
{ {
if (accessor->write_chunk == NULL) if (accessor->write_chunk == NULL)
{ {
@ -339,7 +340,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
} }
/* It may still not be enough in the case of a gigantic tuple. */ /* It may still not be enough in the case of a gigantic tuple. */
if (accessor->write_pointer + size >= accessor->write_end) if (accessor->write_pointer + size > accessor->write_end)
{ {
size_t written; size_t written;