diff options
Diffstat (limited to 'src/backend/executor/execGrouping.c')
| -rw-r--r-- | src/backend/executor/execGrouping.c | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/src/backend/executor/execGrouping.c b/src/backend/executor/execGrouping.c index 94cc59de7e1..3149fbe975c 100644 --- a/src/backend/executor/execGrouping.c +++ b/src/backend/executor/execGrouping.c @@ -18,6 +18,8 @@ */ #include "postgres.h" +#include "access/hash.h" +#include "access/parallel.h" #include "executor/executor.h" #include "miscadmin.h" #include "utils/lsyscache.h" @@ -289,7 +291,8 @@ BuildTupleHashTable(int numCols, AttrNumber *keyColIdx, FmgrInfo *eqfunctions, FmgrInfo *hashfunctions, long nbuckets, Size additionalsize, - MemoryContext tablecxt, MemoryContext tempcxt) + MemoryContext tablecxt, MemoryContext tempcxt, + bool use_variable_hash_iv) { TupleHashTable hashtable; Size entrysize = sizeof(TupleHashEntryData) + additionalsize; @@ -314,6 +317,19 @@ BuildTupleHashTable(int numCols, AttrNumber *keyColIdx, hashtable->in_hash_funcs = NULL; hashtable->cur_eq_funcs = NULL; + /* + * If parallelism is in use, even if the master backend is performing the + * scan itself, we don't want to create the hashtable exactly the same way + * in all workers. As hashtables are iterated over in keyspace-order, + * doing so in all processes in the same way is likely to lead to + * "unbalanced" hashtables when the table size initially is + * underestimated. + */ + if (use_variable_hash_iv) + hashtable->hash_iv = hash_uint32(ParallelWorkerNumber); + else + hashtable->hash_iv = 0; + hashtable->hashtab = tuplehash_create(tablecxt, nbuckets); hashtable->hashtab->private_data = hashtable; @@ -450,7 +466,7 @@ TupleHashTableHash(struct tuplehash_hash *tb, const MinimalTuple tuple) TupleHashTable hashtable = (TupleHashTable) tb->private_data; int numCols = hashtable->numCols; AttrNumber *keyColIdx = hashtable->keyColIdx; - uint32 hashkey = 0; + uint32 hashkey = hashtable->hash_iv; TupleTableSlot *slot; FmgrInfo *hashfunctions; int i; |