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Add header comments to execParallel.c and nodeGather.c.

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Patch by me, per a note from Simon Riggs.  Reviewed by Amit Kapila
and Amit Langote.
This commit is contained in:
Robert Haas
2015-10-22 10:37:24 -04:00
parent e4a618aa1e
commit 1a219fa15b
2 changed files with 22 additions and 0 deletions
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14
src/backend/executor/nodeGather.c
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@ -6,6 +6,20 @@
* Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* A Gather executor launches parallel workers to run multiple copies of a
* plan. It can also run the plan itself, if the workers are not available
* or have not started up yet. It then merges all of the results it produces
* and the results from the workers into a single output stream. Therefore,
* it will normally be used with a plan where running multiple copies of the
* same plan does not produce duplicate output, such as PartialSeqScan.
*
* Alternatively, a Gather node can be configured to use just one worker
* and the single-copy flag can be set. In this case, the Gather node will
* run the plan in one worker and will not execute the plan itself. In
* this case, it simply returns whatever tuples were returned by the worker.
* If a worker cannot be obtained, then it will run the plan itself and
* return the results. Therefore, a plan used with a single-copy Gather
* node need not be parallel-aware.
*
* IDENTIFICATION
* src/backend/executor/nodeGather.c