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Commit909b449

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Fix concurrency issues with WAL segment recycling on Windows
This commit is mostly a revert ofaaa3aed, that switched the routinedoing the internal renaming of recycled WAL segments to use on Windows acombination of CreateHardLinkA() plus unlink() instead of rename(). Asreported by several users of Postgres 13, this is causing concurrencyissues when manipulating WAL segments, mostly in the shape of thefollowing error:LOG: could not rename file "pg_wal/000000XX000000YY000000ZZ":Permission deniedThis moves back to a logic where a single rename() (well, pgrename() forWindows) is used. This issue has proved to be hard to hit when I testedit, facing it only once with an archive_command that was not able to doits work, so it is environment-sensitive. The reporters of this issuehave been able to confirm that the situation improved once we switchedback to a single rename(). In order to check things, I have provided tothe reporters a patched build based on 13.2 withaaa3aed reverted, totest if the error goes away, and an unpatched build of 13.2 to test ifthe error still showed up (just to make sure that I did not mess up mybuild process).Extra thanks to Fujii Masao for pointing out what looked like theculprit commit, and to all the reporters for taking the time to testwhat I have sent them.Reported-by: Andrus, Guy Burgess, Yaroslav Pashinsky, Thomas TrenzReviewed-by: Tom Lane, Andres FreundDiscussion:https://postgr.es/m/3861ff1e-0923-7838-e826-094cc9bef737@hot.eeDiscussion:https://postgr.es/m/16874-c3eecd319e36a2bf@postgresql.orgDiscussion:https://postgr.es/m/095ccf8d-7f58-d928-427c-b17ace23cae6@burgess.co.nzDiscussion:https://postgr.es/m/16927-67c570d968c99567%40postgresql.orgDiscussion:https://postgr.es/m/YFBcRbnBiPdGZvfW@paquier.xyzBackpatch-through: 13
1 parent8c6eda2 commit909b449

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2 files changed

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‎src/backend/storage/file/fd.c

Lines changed: 18 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -801,17 +801,20 @@ durable_unlink(const char *fname, int elevel)
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}
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/*
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* durable_rename_excl -- rename a file in a durable manner, without
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* overwriting an existing target file
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* durable_rename_excl -- rename a file in a durable manner.
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*
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* Similar to durable_rename(), except that this routinewill fail if the
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*target file already exists.
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* Similar to durable_rename(), except that this routinetries (but does not
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*guarantee) not to overwrite the target file.
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*
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* Note that a crash in an unfortunate moment can leave you with two links to
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* the target file.
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*
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* Log errors with the caller specified severity.
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*
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* On Windows, using a hard link followed by unlink() causes concurrency
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* issues, while a simple rename() does not cause that, so be careful when
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* changing the logic of this routine.
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*
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* Returns 0 if the operation succeeded, -1 otherwise. Note that errno is not
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* valid upon return.
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*/
@@ -825,6 +828,7 @@ durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
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if (fsync_fname_ext(oldfile, false, false,elevel)!=0)
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return-1;
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#ifdefHAVE_WORKING_LINK
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if (link(oldfile,newfile)<0)
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{
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ereport(elevel,
@@ -834,6 +838,16 @@ durable_rename_excl(const char *oldfile, const char *newfile, int elevel)
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return-1;
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}
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unlink(oldfile);
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#else
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if (rename(oldfile,newfile)<0)
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{
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ereport(elevel,
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(errcode_for_file_access(),
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errmsg("could not rename file \"%s\" to \"%s\": %m",
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oldfile,newfile)));
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return-1;
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}
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#endif
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/*
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* Make change persistent in case of an OS crash, both the new entry and

‎src/include/pg_config_manual.h

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -135,6 +135,13 @@
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#defineEXEC_BACKEND
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#endif
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/*
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* Define this if your operating system supports link()
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*/
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#if !defined(WIN32)&& !defined(__CYGWIN__)
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#defineHAVE_WORKING_LINK 1
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#endif
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/*
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* USE_POSIX_FADVISE controls whether Postgres will attempt to use the
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* posix_fadvise() kernel call. Usually the automatic configure tests are

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