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Restore foreign-key-aware estimation of join relation sizes.

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This patch provides a new implementation of the logic added by commit
137805f89 and later removed by 77ba61080.  It differs from the original
primarily in expending much less effort per joinrel in large queries,
which it accomplishes by doing most of the matching work once per query not
once per joinrel.  Hopefully, it's also less buggy and better commented.
The never-documented enable_fkey_estimates GUC remains gone.

There remains work to be done to make the selectivity estimates account
for nulls in FK referencing columns; but that was true of the original
patch as well.  We may be able to address this point later in beta.
In the meantime, any error should be in the direction of overestimating
rather than underestimating joinrel sizes, which seems like the direction
we want to err in.

Tomas Vondra and Tom Lane

Discussion: <31041.1465069446@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-06-18 15:22:34 -04:00
parent 598aa194af
commit 100340e2dc
17 changed files with 921 additions and 18 deletions
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32
src/include/nodes/relation.h
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@@ -251,6 +251,8 @@ typedef struct PlannerInfo
List *placeholder_list; /* list of PlaceHolderInfos */
List *fkey_list; /* list of ForeignKeyOptInfos */
List *query_pathkeys; /* desired pathkeys for query_planner() */
List *group_pathkeys; /* groupClause pathkeys, if any */
@@ -622,6 +624,36 @@ typedef struct IndexOptInfo
void (*amcostestimate) (); /* AM's cost estimator */
} IndexOptInfo;
/*
* ForeignKeyOptInfo
* Per-foreign-key information for planning/optimization
*
* The per-FK-column arrays can be fixed-size because we allow at most
* INDEX_MAX_KEYS columns in a foreign key constraint. Each array has
* nkeys valid entries.
*/
typedef struct ForeignKeyOptInfo
{
NodeTag type;
/* Basic data about the foreign key (fetched from catalogs): */
Index con_relid; /* RT index of the referencing table */
Index ref_relid; /* RT index of the referenced table */
int nkeys; /* number of columns in the foreign key */
AttrNumber conkey[INDEX_MAX_KEYS]; /* cols in referencing table */
AttrNumber confkey[INDEX_MAX_KEYS]; /* cols in referenced table */
Oid conpfeqop[INDEX_MAX_KEYS]; /* PK = FK operator OIDs */
/* Derived info about whether FK's equality conditions match the query: */
int nmatched_ec; /* # of FK cols matched by ECs */
int nmatched_rcols; /* # of FK cols matched by non-EC rinfos */
int nmatched_ri; /* total # of non-EC rinfos matched to FK */
/* Pointer to eclass matching each column's condition, if there is one */
struct EquivalenceClass *eclass[INDEX_MAX_KEYS];
/* List of non-EC RestrictInfos matching each column's condition */
List *rinfos[INDEX_MAX_KEYS];
} ForeignKeyOptInfo;
/*
* EquivalenceClasses