diff options
Diffstat (limited to 'src/backend/optimizer/path/costsize.c')
| -rw-r--r-- | src/backend/optimizer/path/costsize.c | 75 |
1 files changed, 43 insertions, 32 deletions
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index bdfbbb18186..7dfe834b779 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -41,7 +41,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.71 2001/05/07 00:43:20 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.72 2001/05/09 00:35:09 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -61,12 +61,6 @@ #include "utils/syscache.h" -/* - * The length of a variable-length field in bytes (stupid estimate...) - */ -#define _DEFAULT_ATTRIBUTE_WIDTH_ 12 - - #define LOG2(x) (log(x) / 0.693147180559945) #define LOG6(x) (log(x) / 1.79175946922805) @@ -90,7 +84,6 @@ bool enable_hashjoin = true; static bool cost_qual_eval_walker(Node *node, Cost *total); static void set_rel_width(Query *root, RelOptInfo *rel); -static int compute_attribute_width(TargetEntry *tlistentry); static double relation_byte_size(double tuples, int width); static double page_size(double tuples, int width); @@ -1082,36 +1075,54 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel, /* * set_rel_width * Set the estimated output width of the relation. + * + * NB: this works best on base relations because it prefers to look at + * real Vars. It will fail to make use of pg_statistic info when applied + * to a subquery relation, even if the subquery outputs are simple vars + * that we could have gotten info for. Is it worth trying to be smarter + * about subqueries? */ static void set_rel_width(Query *root, RelOptInfo *rel) { - int tuple_width = 0; - List *tle; + int32 tuple_width = 0; + List *tllist; - foreach(tle, rel->targetlist) - tuple_width += compute_attribute_width((TargetEntry *) lfirst(tle)); - Assert(tuple_width >= 0); - rel->width = tuple_width; -} + foreach(tllist, rel->targetlist) + { + TargetEntry *tle = (TargetEntry *) lfirst(tllist); + int32 item_width; -/* - * compute_attribute_width - * Given a target list entry, find the size in bytes of the attribute. - * - * If a field is variable-length, we make a default assumption. Would be - * better if VACUUM recorded some stats about the average field width... - * also, we have access to the atttypmod, but fail to use it... - */ -static int -compute_attribute_width(TargetEntry *tlistentry) -{ - int width = get_typlen(tlistentry->resdom->restype); + /* + * If it's a Var, try to get statistical info from pg_statistic. + */ + if (tle->expr && IsA(tle->expr, Var)) + { + Var *var = (Var *) tle->expr; + Oid relid; - if (width < 0) - return _DEFAULT_ATTRIBUTE_WIDTH_; - else - return width; + relid = getrelid(var->varno, root->rtable); + if (relid != InvalidOid) + { + item_width = get_attavgwidth(relid, var->varattno); + if (item_width > 0) + { + tuple_width += item_width; + continue; + } + } + } + /* + * Not a Var, or can't find statistics for it. Estimate using + * just the type info. + */ + item_width = get_typavgwidth(tle->resdom->restype, + tle->resdom->restypmod); + Assert(item_width > 0); + tuple_width += item_width; + } + Assert(tuple_width >= 0); + rel->width = tuple_width; } /* @@ -1122,7 +1133,7 @@ compute_attribute_width(TargetEntry *tlistentry) static double relation_byte_size(double tuples, int width) { - return tuples * ((double) (width + sizeof(HeapTupleData))); + return tuples * ((double) MAXALIGN(width + sizeof(HeapTupleData))); } /* |