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| author | Robert Haas <rhaas@postgresql.org> | 2017-03-23 13:05:48 -0400 |
|---|---|---|
| committer | Robert Haas <rhaas@postgresql.org> | 2017-03-23 13:14:36 -0400 |
| commit | 691b8d59281b5177f16fe80858df921f77a8e955 (patch) | |
| tree | 8708ae434bf120e73f93e3ef43779d761438ba79 /src/include/executor/execdesc.h | |
| parent | 218f51584d5a9fcdf702bcc7f54b5b65e255c187 (diff) | |
| download | postgresql-691b8d59281b5177f16fe80858df921f77a8e955.tar.gz postgresql-691b8d59281b5177f16fe80858df921f77a8e955.zip | |
Allow for parallel execution whenever ExecutorRun() is done only once.
Previously, it was unsafe to execute a plan in parallel if
ExecutorRun() might be called with a non-zero row count. However,
it's quite easy to fix things up so that we can support that case,
provided that it is known that we will never call ExecutorRun() a
second time for the same QueryDesc. Add infrastructure to signal
this, and cross-checks to make sure that a caller who claims this is
true doesn't later reneg.
While that pattern never happens with queries received directly from a
client -- there's no way to know whether multiple Execute messages
will be sent unless the first one requests all the rows -- it's pretty
common for queries originating from procedural languages, which often
limit the result to a single tuple or to a user-specified number of
tuples.
This commit doesn't actually enable parallelism in any additional
cases, because currently none of the places that would be able to
benefit from this infrastructure pass CURSOR_OPT_PARALLEL_OK in the
first place, but it makes it much more palatable to pass
CURSOR_OPT_PARALLEL_OK in places where we currently don't, because it
eliminates some cases where we'd end up having to run the parallel
plan serially.
Patch by me, based on some ideas from Rafia Sabih and corrected by
Rafia Sabih based on feedback from Dilip Kumar and myself.
Discussion: http://postgr.es/m/CA+TgmobXEhvHbJtWDuPZM9bVSLiTj-kShxQJ2uM5GPDze9fRYA@mail.gmail.com
Diffstat (limited to 'src/include/executor/execdesc.h')
| -rw-r--r-- | src/include/executor/execdesc.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/src/include/executor/execdesc.h b/src/include/executor/execdesc.h index c99ea818158..87e7ca85082 100644 --- a/src/include/executor/execdesc.h +++ b/src/include/executor/execdesc.h @@ -47,6 +47,9 @@ typedef struct QueryDesc EState *estate; /* executor's query-wide state */ PlanState *planstate; /* tree of per-plan-node state */ + /* This field is set by ExecutorRun */ + bool already_executed; /* true if previously executed */ + /* This is always set NULL by the core system, but plugins can change it */ struct Instrumentation *totaltime; /* total time spent in ExecutorRun */ } QueryDesc; |