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Avoid misbehavior when hash_table_bytes < bucket_size.

It's possible to reach this case when work_mem is very small and tupsizeis (relatively) very large. In that case ExecChooseHashTableSize wouldget 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 in28d9360.Back-patch to v13, as that was.Zhang MingliDiscussion:https://postgr.es/m/beb64ca0-91e2-44ac-bf4a-7ea36275ec02@Spark

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src/backend/executor
- nodeHash.c

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`‎src/backend/executor/nodeHash.c`

Lines changed: 4 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -832,7 +832,10 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,`
`832`	`832`	`* overhead for the hash code, pointer to the next tuple, etc.`
`833`	`833`	`*/`
`834`	`834`	`bucket_size= (tupsize*NTUP_PER_BUCKET+sizeof(HashJoinTuple));`
`835`		`-sbuckets=pg_nextpower2_size_t(hash_table_bytes /bucket_size);`
	`835`	`+if (hash_table_bytes <=bucket_size)`
	`836`	`+sbuckets=1;/* avoid pg_nextpower2_size_t(0) */`
	`837`	`+else`
	`838`	`+sbuckets=pg_nextpower2_size_t(hash_table_bytes /bucket_size);`
`836`	`839`	`sbuckets=Min(sbuckets,max_pointers);`
`837`	`840`	`nbuckets= (int)sbuckets;`
`838`	`841`	`nbuckets=pg_nextpower2_32(nbuckets);`

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Commit4878ea7

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`‎src/backend/executor/nodeHash.c`

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