database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-07 00:36:50 +03:00
Code Activity

Prohibit pushing subqueries containing window function calculation to

Browse Source 
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
This commit is contained in:
Amit Kapila
2018-09-04 10:26:06 +05:30
parent 16e7bcfac5
commit 2ce253cf57
3 changed files with 47 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
src/backend/optimizer/util/clauses.c
View File

@ -1190,12 +1190,26 @@ 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.
*/