diff options
Diffstat (limited to 'src/backend/optimizer/plan/planner.c')
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 25 |
1 files changed, 20 insertions, 5 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index 74e7258bba2..a6ad9dbdcec 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.232 2008/04/17 21:22:14 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.233 2008/05/02 21:26:09 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -42,6 +42,9 @@ #include "utils/syscache.h" +/* GUC parameter */ +double cursor_tuple_fraction = DEFAULT_CURSOR_TUPLE_FRACTION; + /* Hook for plugins to get control in planner() */ planner_hook_type planner_hook = NULL; @@ -142,11 +145,23 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams) { /* * We have no real idea how many tuples the user will ultimately FETCH - * from a cursor, but it seems a good bet that he doesn't want 'em - * all. Optimize for 10% retrieval (you gotta better number? Should - * this be a SETtable parameter?) + * from a cursor, but it is often the case that he doesn't want 'em + * all, or would prefer a fast-start plan anyway so that he can + * process some of the tuples sooner. Use a GUC parameter to decide + * what fraction to optimize for. + */ + tuple_fraction = cursor_tuple_fraction; + + /* + * We document cursor_tuple_fraction as simply being a fraction, + * which means the edge cases 0 and 1 have to be treated specially + * here. We convert 1 to 0 ("all the tuples") and 0 to a very small + * fraction. */ - tuple_fraction = 0.10; + if (tuple_fraction >= 1.0) + tuple_fraction = 0.0; + else if (tuple_fraction <= 0.0) + tuple_fraction = 1e-10; } else { |