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| author | Amit Kapila <akapila@postgresql.org> | 2018-09-04 10:49:05 +0530 |
|---|---|---|
| committer | Amit Kapila <akapila@postgresql.org> | 2018-09-04 10:49:05 +0530 |
| commit | bf61873ae3b64e2883c1a9c7af8e5df788a7123c (patch) | |
| tree | 91305bf35c63a017136ec8c0c61526a1dc1477cc /src/backend | |
| parent | 3b7a96a619f78f80b4a470a0dcde4c92b5b7141f (diff) | |
| download | postgresql-bf61873ae3b64e2883c1a9c7af8e5df788a7123c.tar.gz postgresql-bf61873ae3b64e2883c1a9c7af8e5df788a7123c.zip | |
Prohibit pushing subqueries containing window function calculation to
workers.
Allowing window function calculation in workers leads to inconsistent
results because if the input row ordering is not fully deterministic, the
output of window functions might vary across workers. The fix is to treat
them as parallel-restricted.
In the passing, improve the coding pattern in max_parallel_hazard_walker
so that it has a chain of mutually-exclusive if ... else if ... else if
... else if ... IsA tests.
Reported-by: Marko Tiikkaja
Bug: 15324
Author: Amit Kapila
Reviewed-by: Tom Lane
Backpatch-through: 9.6
Discussion: https://postgr.es/m/CAL9smLAnfPJCDUUG4ckX2iznj53V7VSMsYefzZieN93YxTNOcw@mail.gmail.com
Diffstat (limited to 'src/backend')
| -rw-r--r-- | src/backend/optimizer/util/clauses.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index fa53b7a8c50..82b56902a6c 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -1168,13 +1168,27 @@ max_parallel_hazard_walker(Node *node, max_parallel_hazard_context *context) return true; } - if (IsA(node, NextValueExpr)) + else if (IsA(node, NextValueExpr)) { if (max_parallel_hazard_test(PROPARALLEL_UNSAFE, context)) return true; } /* + * Treat window functions as parallel-restricted because we aren't sure + * whether the input row ordering is fully deterministic, and the output + * of window functions might vary across workers if not. (In some cases, + * like where the window frame orders by a primary key, we could relax + * this restriction. But it doesn't currently seem worth expending extra + * effort to do so.) + */ + else if (IsA(node, WindowFunc)) + { + if (max_parallel_hazard_test(PROPARALLEL_RESTRICTED, context)) + return true; + } + + /* * As a notational convenience for callers, look through RestrictInfo. */ else if (IsA(node, RestrictInfo)) |