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Commitb3c4e24

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In pgwin32_open, loop after ERROR_ACCESS_DENIED only if we can't stat.
This fixes a performance problem introduced by commit6d7547c.ERROR_ACCESS_DENIED is returned in some other cases besides thedelete-pending case considered by that commit; notably, if thegiven path names a directory instead of a plain file. In thatcase we'll uselessly loop for 1 second before returning thefailure condition. That slows down some usage scenarios enoughto cause test timeout failures on our Windows buildfarm critters.To fix, try to stat() the file, and sleep/loop only if that fails.It will fail in the delete-pending case, and also in the case wherethe deletion completed before we could stat(), so we have the caseswhere we want to loop covered. In the directory case, the stat()should succeed, letting us exit without a wait.One case where we'll still wait uselessly is if the access-deniedproblem pertains to a directory in the given pathname. But we don'texpect that to happen in any performance-critical code path.There might be room to refine this further, but I'll push it nowin hopes of making the buildfarm green again.Back-patch, like the preceding commit.Alexander Lakhin and Tom LaneDiscussion:https://postgr.es/m/23073.1576626626@sss.pgh.pa.us
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‎src/port/open.c

Lines changed: 23 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@
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#include<fcntl.h>
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#include<assert.h>
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#include<sys/stat.h>
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staticint
@@ -120,18 +121,33 @@ pgwin32_open(const char *fileName, int fileFlags,...)
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}
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/*
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* ERROR_ACCESS_DENIED can be returned if the file is deleted but not
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* yet gone (Windows NT status code is STATUS_DELETE_PENDING). Wait a
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* bit and try again, giving up after 1 second (since this condition
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* should never persist very long).
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* ERROR_ACCESS_DENIED is returned if the file is deleted but not yet
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* gone (Windows NT status code is STATUS_DELETE_PENDING). In that
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* case we want to wait a bit and try again, giving up after 1 second
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* (since this condition should never persist very long). However,
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* there are other commonly-hit cases that return ERROR_ACCESS_DENIED,
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* so care is needed. In particular that happens if we try to open a
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* directory, or of course if there's an actual file-permissions
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* problem. To distinguish these cases, try a stat(). In the
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* delete-pending case, it will either also get STATUS_DELETE_PENDING,
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* or it will see the file as gone and fail with ENOENT. In other
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* cases it will usually succeed. The only somewhat-likely case where
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* this coding will uselessly wait is if there's a permissions problem
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* with a containing directory, which we hope will never happen in any
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* performance-critical code paths.
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*/
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if (err==ERROR_ACCESS_DENIED)
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{
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if (loops<10)
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{
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pg_usleep(100000);
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loops++;
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continue;
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structstatst;
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if (stat(fileName,&st)!=0)
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{
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pg_usleep(100000);
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loops++;
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continue;
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}
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}
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}
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