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| author | Robert Haas <rhaas@postgresql.org> | 2015-12-22 13:57:18 -0500 |
|---|---|---|
| committer | Robert Haas <rhaas@postgresql.org> | 2015-12-22 13:59:13 -0500 |
| commit | 120b31dc5406cf004b99150b84b48dc312577eca (patch) | |
| tree | 3f1c4615d8afeecdf078eeaca5a3be413fe7f3da /src/backend/utils | |
| parent | 496943ec2b6de0f22cd9e18f673e13635b5972ef (diff) | |
| download | postgresql-120b31dc5406cf004b99150b84b48dc312577eca.tar.gz postgresql-120b31dc5406cf004b99150b84b48dc312577eca.zip | |
Comment improvements for abbreviated keys.
Peter Geoghegan and Robert Haas
Diffstat (limited to 'src/backend/utils')
| -rw-r--r-- | src/backend/utils/sort/tuplesort.c | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c index 6572af875a5..cf1cdcbeab5 100644 --- a/src/backend/utils/sort/tuplesort.c +++ b/src/backend/utils/sort/tuplesort.c @@ -930,7 +930,14 @@ tuplesort_begin_datum(Oid datumType, Oid sortOperator, Oid sortCollation, state->sortKeys->ssup_collation = sortCollation; state->sortKeys->ssup_nulls_first = nullsFirstFlag; - /* abbreviation is possible here only for by-reference types */ + /* + * Abbreviation is possible here only for by-reference types. In theory, + * a pass-by-value datatype could have an abbreviated form that is cheaper + * to compare. In a tuple sort, we could support that, because we can + * always extract the original datum from the tuple is needed. Here, we + * can't, because a datum sort only stores a single copy of the datum; + * the "tuple" field of each sortTuple is NULL. + */ state->sortKeys->abbreviate = !typbyval; PrepareSortSupportFromOrderingOp(sortOperator, state->sortKeys); @@ -1271,7 +1278,7 @@ tuplesort_putindextuplevalues(Tuplesortstate *state, Relation rel, * Store ordinary Datum representation, or NULL value. If there is a * converter it won't expect NULL values, and cost model is not * required to account for NULL, so in that case we avoid calling - * converter and just set datum1 to "void" representation (to be + * converter and just set datum1 to zeroed representation (to be * consistent). */ stup.datum1 = original; @@ -3155,7 +3162,7 @@ copytup_heap(Tuplesortstate *state, SortTuple *stup, void *tup) * Store ordinary Datum representation, or NULL value. If there is a * converter it won't expect NULL values, and cost model is not * required to account for NULL, so in that case we avoid calling - * converter and just set datum1 to "void" representation (to be + * converter and just set datum1 to zeroed representation (to be * consistent). */ stup->datum1 = original; @@ -3397,7 +3404,7 @@ copytup_cluster(Tuplesortstate *state, SortTuple *stup, void *tup) * Store ordinary Datum representation, or NULL value. If there is a * converter it won't expect NULL values, and cost model is not * required to account for NULL, so in that case we avoid calling - * converter and just set datum1 to "void" representation (to be + * converter and just set datum1 to zeroed representation (to be * consistent). */ stup->datum1 = original; @@ -3701,7 +3708,7 @@ copytup_index(Tuplesortstate *state, SortTuple *stup, void *tup) * Store ordinary Datum representation, or NULL value. If there is a * converter it won't expect NULL values, and cost model is not * required to account for NULL, so in that case we avoid calling - * converter and just set datum1 to "void" representation (to be + * converter and just set datum1 to zeroed representation (to be * consistent). */ stup->datum1 = original; |