diff options
Diffstat (limited to 'src/backend/commands/statscmds.c')
| -rw-r--r-- | src/backend/commands/statscmds.c | 82 |
1 files changed, 71 insertions, 11 deletions
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c index 8274792a778..790593b1ab3 100644 --- a/src/backend/commands/statscmds.c +++ b/src/backend/commands/statscmds.c @@ -73,11 +73,12 @@ CreateStatistics(CreateStatsStmt *stmt) Oid relid; ObjectAddress parentobject, myself; - Datum types[2]; /* one for each possible type of statistic */ + Datum types[3]; /* one for each possible type of statistic */ int ntypes; ArrayType *stxkind; bool build_ndistinct; bool build_dependencies; + bool build_mcv; bool requested_type = false; int i; ListCell *cell; @@ -272,6 +273,7 @@ CreateStatistics(CreateStatsStmt *stmt) */ build_ndistinct = false; build_dependencies = false; + build_mcv = false; foreach(cell, stmt->stat_types) { char *type = strVal((Value *) lfirst(cell)); @@ -286,6 +288,11 @@ CreateStatistics(CreateStatsStmt *stmt) build_dependencies = true; requested_type = true; } + else if (strcmp(type, "mcv") == 0) + { + build_mcv = true; + requested_type = true; + } else ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), @@ -297,6 +304,7 @@ CreateStatistics(CreateStatsStmt *stmt) { build_ndistinct = true; build_dependencies = true; + build_mcv = true; } /* construct the char array of enabled statistic types */ @@ -305,6 +313,8 @@ CreateStatistics(CreateStatsStmt *stmt) types[ntypes++] = CharGetDatum(STATS_EXT_NDISTINCT); if (build_dependencies) types[ntypes++] = CharGetDatum(STATS_EXT_DEPENDENCIES); + if (build_mcv) + types[ntypes++] = CharGetDatum(STATS_EXT_MCV); Assert(ntypes > 0 && ntypes <= lengthof(types)); stxkind = construct_array(types, ntypes, CHAROID, 1, true, 'c'); @@ -329,6 +339,7 @@ CreateStatistics(CreateStatsStmt *stmt) /* no statistics built yet */ nulls[Anum_pg_statistic_ext_stxndistinct - 1] = true; nulls[Anum_pg_statistic_ext_stxdependencies - 1] = true; + nulls[Anum_pg_statistic_ext_stxmcv - 1] = true; /* insert it into pg_statistic_ext */ htup = heap_form_tuple(statrel->rd_att, values, nulls); @@ -424,23 +435,72 @@ RemoveStatisticsById(Oid statsOid) * null until the next ANALYZE. (Note that the type change hasn't actually * happened yet, so one option that's *not* on the table is to recompute * immediately.) + * + * For both ndistinct and functional-dependencies stats, the on-disk + * representation is independent of the source column data types, and it is + * plausible to assume that the old statistic values will still be good for + * the new column contents. (Obviously, if the ALTER COLUMN TYPE has a USING + * expression that substantially alters the semantic meaning of the column + * values, this assumption could fail. But that seems like a corner case + * that doesn't justify zapping the stats in common cases.) + * + * For MCV lists that's not the case, as those statistics store the datums + * internally. In this case we simply reset the statistics value to NULL. */ void UpdateStatisticsForTypeChange(Oid statsOid, Oid relationOid, int attnum, Oid oldColumnType, Oid newColumnType) { + HeapTuple stup, + oldtup; + + Relation rel; + + Datum values[Natts_pg_statistic_ext]; + bool nulls[Natts_pg_statistic_ext]; + bool replaces[Natts_pg_statistic_ext]; + + oldtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(statsOid)); + if (!oldtup) + elog(ERROR, "cache lookup failed for statistics object %u", statsOid); + /* - * Currently, we don't actually need to do anything here. For both - * ndistinct and functional-dependencies stats, the on-disk representation - * is independent of the source column data types, and it is plausible to - * assume that the old statistic values will still be good for the new - * column contents. (Obviously, if the ALTER COLUMN TYPE has a USING - * expression that substantially alters the semantic meaning of the column - * values, this assumption could fail. But that seems like a corner case - * that doesn't justify zapping the stats in common cases.) - * - * Future types of extended stats will likely require us to work harder. + * When none of the defined statistics types contain datum values + * from the table's columns then there's no need to reset the stats. + * Functional dependencies and ndistinct stats should still hold true. */ + if (!statext_is_kind_built(oldtup, STATS_EXT_MCV)) + { + ReleaseSysCache(oldtup); + return; + } + + /* + * OK, we need to reset some statistics. So let's build the new tuple, + * replacing the affected statistics types with NULL. + */ + memset(nulls, 0, Natts_pg_statistic_ext * sizeof(bool)); + memset(replaces, 0, Natts_pg_statistic_ext * sizeof(bool)); + memset(values, 0, Natts_pg_statistic_ext * sizeof(Datum)); + + replaces[Anum_pg_statistic_ext_stxmcv - 1] = true; + nulls[Anum_pg_statistic_ext_stxmcv - 1] = true; + + rel = heap_open(StatisticExtRelationId, RowExclusiveLock); + + /* replace the old tuple */ + stup = heap_modify_tuple(oldtup, + RelationGetDescr(rel), + values, + nulls, + replaces); + + ReleaseSysCache(oldtup); + CatalogTupleUpdate(rel, &stup->t_self, stup); + + heap_freetuple(stup); + + heap_close(rel, RowExclusiveLock); } /* |