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Add new FDW API to test for parallel-safety.

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This is basically a bug fix; the old code assumes that a ForeignScan
is always parallel-safe, but for postgres_fdw, for example, this is
definitely false.  It should be true for file_fdw, though, since a
worker can read a file from the filesystem just as well as any other
backend process.

Original patch by Thomas Munro.  Documentation, and changes to the
comments, by me.
This commit is contained in:
Robert Haas
2016-02-26 16:14:46 +05:30
parent 9117985b6b
commit 35746bc348
4 changed files with 60 additions and 0 deletions
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15
contrib/file_fdw/file_fdw.c
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@ -131,6 +131,8 @@ static void fileEndForeignScan(ForeignScanState *node);
static bool fileAnalyzeForeignTable(Relation relation,
AcquireSampleRowsFunc *func,
BlockNumber *totalpages);
static bool fileIsForeignScanParallelSafe(PlannerInfo *root, RelOptInfo *rel,
RangeTblEntry *rte);
/*
* Helper functions
@ -170,6 +172,7 @@ file_fdw_handler(PG_FUNCTION_ARGS)
fdwroutine->ReScanForeignScan = fileReScanForeignScan;
fdwroutine->EndForeignScan = fileEndForeignScan;
fdwroutine->AnalyzeForeignTable = fileAnalyzeForeignTable;
fdwroutine->IsForeignScanParallelSafe = fileIsForeignScanParallelSafe;
PG_RETURN_POINTER(fdwroutine);
}
@ -761,6 +764,18 @@ fileAnalyzeForeignTable(Relation relation,
return true;
}
/*
* fileIsForeignScanParallelSafe
* Reading a file in a parallel worker should work just the same as
* reading it in the leader, so mark scans safe.
*/
static bool
fileIsForeignScanParallelSafe(PlannerInfo *root, RelOptInfo *rel,
RangeTblEntry *rte)
{
return true;
}
/*
* check_selective_binary_conversion
*