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commit    1a5afe007779b677c4f2e411f8d9af23f7a2d085
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Thu Jan 26 01:50:07 2023 +0000
First released in: 16.0, 11.19, 12.14, 13.10, 14.7, 15.2

    Fix rare sharedtuplestore.c corruption.
    
    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


 src/backend/utils/sort/sharedtuplestore.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/backend/utils/sort/sharedtuplestore.c b/src/backend/utils/sort/sharedtuplestore.c
index 5897a6c1dd9..ec3eeced4e2 100644
--- a/src/backend/utils/sort/sharedtuplestore.c
+++ b/src/backend/utils/sort/sharedtuplestore.c
@@ -158,6 +158,7 @@ sts_initialize(SharedTuplestore *sts, int participants,
 		LWLockInitialize(&sts->participants[i].lock,
 						 LWTRANCHE_SHARED_TUPLESTORE);
 		sts->participants[i].read_page = 0;
+		sts->participants[i].npages = 0;
 		sts->participants[i].writing = false;
 	}
 
@@ -319,7 +320,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
 
 	/* Do we have space? */
 	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)
 		{
@@ -339,7 +340,7 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
 		}
 
 		/* 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;
 


[parent: c5864805ba99]