diff options
Diffstat (limited to 'src/backend/utils/adt/selfuncs.c')
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 2e3fab6a958..e6837869cf6 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -113,6 +113,7 @@ #include "catalog/pg_statistic.h" #include "catalog/pg_statistic_ext.h" #include "executor/executor.h" +#include "executor/nodeAgg.h" #include "miscadmin.h" #include "nodes/makefuncs.h" #include "nodes/nodeFuncs.h" @@ -3428,6 +3429,43 @@ estimate_hash_bucket_stats(PlannerInfo *root, Node *hashkey, double nbuckets, ReleaseVariableStats(vardata); } +/* + * estimate_hashagg_tablesize + * estimate the number of bytes that a hash aggregate hashtable will + * require based on the agg_costs, path width and number of groups. + * + * We return the result as "double" to forestall any possible overflow + * problem in the multiplication by dNumGroups. + * + * XXX this may be over-estimating the size now that hashagg knows to omit + * unneeded columns from the hashtable. Also for mixed-mode grouping sets, + * grouping columns not in the hashed set are counted here even though hashagg + * won't store them. Is this a problem? + */ +double +estimate_hashagg_tablesize(Path *path, const AggClauseCosts *agg_costs, + double dNumGroups) +{ + Size hashentrysize; + + /* Estimate per-hash-entry space at tuple width... */ + hashentrysize = MAXALIGN(path->pathtarget->width) + + MAXALIGN(SizeofMinimalTupleHeader); + + /* plus space for pass-by-ref transition values... */ + hashentrysize += agg_costs->transitionSpace; + /* plus the per-hash-entry overhead */ + hashentrysize += hash_agg_entry_size(agg_costs->numAggs); + + /* + * Note that this disregards the effect of fill-factor and growth policy + * of the hash table. That's probably ok, given that the default + * fill-factor is relatively high. It'd be hard to meaningfully factor in + * "double-in-size" growth policies here. + */ + return hashentrysize * dNumGroups; +} + /*------------------------------------------------------------------------- * |