postgres.git / summary / log / commit / refs

commit    1dfc9193af7ff3cde963aa153e21fadbfebe030a
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sat Aug 13 20:59:58 2022 +0000

    Avoid misbehavior when hash_table_bytes < bucket_size.
    
    It's possible to reach this case when work_mem is very small and tupsize
    is (relatively) very large.  In that case ExecChooseHashTableSize would
    get an assertion failure, or with asserts off it'd compute nbuckets = 0,
    which'd likely cause misbehavior later (I've not checked).  To fix,
    clamp the number of buckets to be at least 1.
    
    This is due to faulty conversion of old my_log2() coding in 28d936031.
    Back-patch to v13, as that was.
    
    Zhang Mingli
    
    Discussion: https://postgr.es/m/beb64ca0-91e2-44ac-bf4a-7ea36275ec02@Spark


 src/backend/executor/nodeHash.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index 15d8bbe368c..c0aa95fd3d1 100644
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -832,7 +832,10 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
 		 * overhead for the hash code, pointer to the next tuple, etc.
 		 */
 		bucket_size = (tupsize * NTUP_PER_BUCKET + sizeof(HashJoinTuple));
-		sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
+		if (hash_table_bytes <= bucket_size)
+			sbuckets = 1;		/* avoid pg_nextpower2_size_t(0) */
+		else
+			sbuckets = pg_nextpower2_size_t(hash_table_bytes / bucket_size);
 		sbuckets = Min(sbuckets, max_pointers);
 		nbuckets = (int) sbuckets;
 		nbuckets = pg_nextpower2_32(nbuckets);


[parent: 496ab1d6c8d8]