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| author | David Rowley <drowley@postgresql.org> | 2024-02-15 13:13:31 +1300 |
|---|---|---|
| committer | David Rowley <drowley@postgresql.org> | 2024-02-15 13:13:31 +1300 |
| commit | 87027cb55bf7b33416880f7f5f5e67f4202d5881 (patch) | |
| tree | 8aa0e6312b9312ee396cbccb2a585febf1130e81 /src/backend/optimizer/util/pathnode.c | |
| parent | 8fd0498de2005b4136aaf6fcd056ca4b18e37724 (diff) | |
| download | postgresql-87027cb55bf7b33416880f7f5f5e67f4202d5881.tar.gz postgresql-87027cb55bf7b33416880f7f5f5e67f4202d5881.zip | |
Clarify the 'rows' parameter in create_append_path
This is extracted from a larger patch to improve the UNION planner.
While working on that, I found myself having to check what the 'rows'
parameter is for. It's not obvious that passing a negative number is the
way to have the rows estimate calculated and to find that out you need
to read code in create_append_path() and in cost_append().
Discussion: https://postgr.es/m/CAApHDvpb_63XQodmxKUF8vb9M7CxyUyT4sWvEgqeQU-GB7QFoQ@mail.gmail.com
Diffstat (limited to 'src/backend/optimizer/util/pathnode.c')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index 2e1ec41a541..b3902b00329 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -1237,6 +1237,10 @@ create_tidrangescan_path(PlannerInfo *root, RelOptInfo *rel, * * Note that we must handle subpaths = NIL, representing a dummy access path. * Also, there are callers that pass root = NULL. + * + * 'rows', when passed as a non-negative number, will be used to overwrite the + * returned path's row estimate. Otherwise, the row estimate is calculated + * by totalling the row estimates from the 'subpaths' list. */ AppendPath * create_append_path(PlannerInfo *root, |