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Further twiddling of nodeHash.c hashtable sizing calculation.

On reflection, the submitted patch didn't really work to prevent therequest size from exceeding MaxAllocSize, because of the fact that we'dhappily round nbuckets up to the next power of 2 after we'd limited it tomax_pointers. The simplest way to enforce the limit correctly is toround max_pointers down to a power of 2 when it isn't one already.(Note that the constraint to INT_MAX / 2, if it were doing anything usefulat all, is properly applied after that.)

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src/backend/executor
- nodeHash.c

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`‎src/backend/executor/nodeHash.c`

Lines changed: 9 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -415,6 +415,7 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,`
`415`	`415`	`longhash_table_bytes;`
`416`	`416`	`longskew_table_bytes;`
`417`	`417`	`longmax_pointers;`
	`418`	`+longmppow2;`
`418`	`419`	`intnbatch=1;`
`419`	`420`	`intnbuckets;`
`420`	`421`	`doubledbuckets;`
`@@ -485,14 +486,20 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,`
`485`	`486`	`*/`
`486`	`487`	`max_pointers= (work_mem*1024L) /sizeof(HashJoinTuple);`
`487`	`488`	`max_pointers=Min(max_pointers,MaxAllocSize /sizeof(HashJoinTuple));`
`488`		`-/* also ensure we avoid integer overflow in nbatch and nbuckets */`
	`489`	`+/* If max_pointers isn't a power of 2, must round it down to one */`
	`490`	`+mppow2=1L <<my_log2(max_pointers);`
	`491`	`+if (max_pointers!=mppow2)`
	`492`	`+max_pointers=mppow2 /2;`
	`493`	`+`
	`494`	`+/* Also ensure we avoid integer overflow in nbatch and nbuckets */`
`489`	`495`	`/* (this step is redundant given the current value of MaxAllocSize) */`
`490`	`496`	`max_pointers=Min(max_pointers,INT_MAX /2);`
`491`	`497`
`492`	`498`	`dbuckets=ceil(ntuples /NTUP_PER_BUCKET);`
`493`	`499`	`dbuckets=Min(dbuckets,max_pointers);`
	`500`	`+nbuckets= (int)dbuckets;`
`494`	`501`	`/* don't let nbuckets be really small, though ... */`
`495`		`-nbuckets=Max((int)dbuckets,1024);`
	`502`	`+nbuckets=Max(nbuckets,1024);`
`496`	`503`	`/* ... and force it to be a power of 2. */`
`497`	`504`	`nbuckets=1 <<my_log2(nbuckets);`
`498`	`505`

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Commitf2fc98f

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`‎src/backend/executor/nodeHash.c`

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