From 8ffc337621f8a287350a7a55256b58b0585f7a1f Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Tue, 26 Apr 2022 11:56:50 -0700 Subject: [PATCH v4 1/2] Replace calls to durable_rename_excl() with durable_rename(). durable_rename_excl() attempts to avoid overwriting any existing files by using link() and unlink(), but it falls back to rename() on some platforms (e.g., Windows), which offers no such overwrite protection. Most callers use durable_rename_excl() just in case there is an existing file, but in practice there shouldn't be one. basic_archive used it to avoid overwriting an archive concurrently created by another server, but as mentioned above, it will still overwrite files on some platforms. Furthermore, failures during durable_rename_excl() can result in multiple hard links to the same file. My testing demonstrated that it was possible to end up with two links to the same file in pg_wal after a crash just before unlink() during WAL recycling. Specifically, the test produced links to the same file for the current WAL file and the next one because the half-recycled WAL file was re-recycled upon restarting. This seems likely to lead to WAL corruption. This change replaces all calls to durable_rename_excl() with durable_rename(). This removes the protection against accidentally overwriting an existing file, but some platforms are already living without it, and ordinarily there shouldn't be one. The function itself is left around in case any extensions are using it. It will be removed in v16 via a follow-up commit. Back-patch to all supported versions. Before v13, durable_rename_excl() was named durable_link_or_rename(). Author: Nathan Bossart Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier Discussion: https://postgr.es/m/20220418182336.GA2298576%40nathanxps13 --- contrib/basic_archive/basic_archive.c | 5 +++-- src/backend/access/transam/timeline.c | 16 ++++------------ src/backend/access/transam/xlog.c | 9 +++------ 3 files changed, 10 insertions(+), 20 deletions(-) diff --git a/contrib/basic_archive/basic_archive.c b/contrib/basic_archive/basic_archive.c index e7efbfb9c3..ed33854c57 100644 --- a/contrib/basic_archive/basic_archive.c +++ b/contrib/basic_archive/basic_archive.c @@ -281,9 +281,10 @@ basic_archive_file_internal(const char *file, const char *path) /* * Sync the temporary file to disk and move it to its final destination. - * This will fail if destination already exists. + * Note that this will overwrite any existing file, but this is only + * possible if someone else created the file since the stat() above. */ - (void) durable_rename_excl(temp, destination, ERROR); + (void) durable_rename(temp, destination, ERROR); ereport(DEBUG1, (errmsg("archived \"%s\" via basic_archive", file))); diff --git a/src/backend/access/transam/timeline.c b/src/backend/access/transam/timeline.c index be21968293..f3a8e53aa4 100644 --- a/src/backend/access/transam/timeline.c +++ b/src/backend/access/transam/timeline.c @@ -441,12 +441,8 @@ writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI, * Now move the completed history file into place with its final name. */ TLHistoryFilePath(path, newTLI); - - /* - * Perform the rename using link if available, paranoidly trying to avoid - * overwriting an existing file (there shouldn't be one). - */ - durable_rename_excl(tmppath, path, ERROR); + Assert(access(path, F_OK) != 0 && errno == ENOENT); + durable_rename(tmppath, path, ERROR); /* The history file can be archived immediately. */ if (XLogArchivingActive()) @@ -519,12 +515,8 @@ writeTimeLineHistoryFile(TimeLineID tli, char *content, int size) * Now move the completed history file into place with its final name. */ TLHistoryFilePath(path, tli); - - /* - * Perform the rename using link if available, paranoidly trying to avoid - * overwriting an existing file (there shouldn't be one). - */ - durable_rename_excl(tmppath, path, ERROR); + Assert(access(path, F_OK) != 0 && errno == ENOENT); + durable_rename(tmppath, path, ERROR); } /* diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 61cda56c6f..76ec80c950 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -3323,14 +3323,11 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath, } } - /* - * Perform the rename using link if available, paranoidly trying to avoid - * overwriting an existing file (there shouldn't be one). - */ - if (durable_rename_excl(tmppath, path, LOG) != 0) + Assert(access(path, F_OK) != 0 && errno == ENOENT); + if (durable_rename(tmppath, path, LOG) != 0) { LWLockRelease(ControlFileLock); - /* durable_rename_excl already emitted log message */ + /* durable_rename already emitted log message */ return false; } -- 2.25.1