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commit    ff4cbc1ff3d23fe9c40110c8953e0d07457b136b
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sun Oct 04 18:16:59 2015 +0000

    Fix possible "invalid memory alloc request size" failure in nodeHash.c.
    
    Limit the size of the hashtable pointer array to not more than
    MaxAllocSize.  We've seen reports of failures due to this in HEAD/9.5,
    and it seems possible in older branches as well.  The change in
    NTUP_PER_BUCKET in 9.5 may have made the problem more likely, but
    surely it didn't introduce it.
    
    Tomas Vondra, slightly modified by me


 src/backend/executor/nodeHash.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index 6917d3f4e6c..5ea353afe38 100644
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -460,10 +460,12 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
 	 * Set nbuckets to achieve an average bucket load of NTUP_PER_BUCKET when
 	 * memory is filled.  Set nbatch to the smallest power of 2 that appears
 	 * sufficient.  The Min() steps limit the results so that the pointer
-	 * arrays we'll try to allocate do not exceed work_mem.
+	 * arrays we'll try to allocate do not exceed work_mem nor MaxAllocSize.
 	 */
-	max_pointers = (work_mem * 1024L) / sizeof(void *);
+	max_pointers = (work_mem * 1024L) / sizeof(HashJoinTuple);
+	max_pointers = Min(max_pointers, MaxAllocSize / sizeof(HashJoinTuple));
 	/* also ensure we avoid integer overflow in nbatch and nbuckets */
+	/* (this step is redundant given the current value of MaxAllocSize) */
 	max_pointers = Min(max_pointers, INT_MAX / 2);
 
 	if (inner_rel_bytes > hash_table_bytes)


[parent: 99557984bc91]