7 Commits (0778eb79b1e2957743bbd577fc3d862a3dc007cf)

Author	SHA1	Message	Date
Andres Freund	fd4bad1655	Remove now superfluous declarations of dlsym()ed symbols. ... The prior commit declared them centrally. Author: Andres Freund <andres@anarazel.de> Reviewed-By: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/20211101020311.av6hphdl6xbjbuif@alap3.anarazel.de	4 years ago
Michael Paquier	dac1ff3090	Replace durable_rename_excl() by durable_rename(), take two ... durable_rename_excl() attempts to avoid overwriting any existing files by using link() and unlink(), and it falls back to rename() on some platforms (aka WIN32), 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 (see below for more details). Furthermore, failures during durable_rename_excl() can result in multiple hard links to the same file. As per Nathan's tests, it is 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, leading to WAL corruption. This change replaces all the calls of durable_rename_excl() to 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 on HEAD via a follow-up commit. Here is a summary of the existing callers of durable_rename_excl() (see second discussion link at the bottom), replaced by this commit. First, 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. Second, xlog.c uses it to recycle past WAL segments, where an overwrite should not happen (origin of the change at f0e37a8) because there are protections about the WAL segment to select when recycling an entry. The third and last area is related to the write of timeline history files. writeTimeLineHistory() will write a new timeline history file at the end of recovery on promotion, so there should be no such files for the same timeline. What remains is writeTimeLineHistoryFile(), that can be used in parallel by a WAL receiver and the startup process, and some digging of the buildfarm shows that EEXIST from a WAL receiver can happen with an error of "could not link file \"pg_wal/xlogtemp.NN\" to \"pg_wal/MM.history\", which would cause an automatic restart of the WAL receiver as it is promoted to FATAL, hence this should improve the stability of the WAL receiver as rename() would overwrite an existing TLI history file already fetched by the startup process at recovery. This is a bug fix, but knowing the unlikeliness of the problem involving one or more crashes at an exceptionally bad moment, no backpatch is done. Also, I want to be careful with such changes (aaa3aed did the opposite of this change by removing HAVE_WORKING_LINK so as Windows would do a link() rather than a rename() but this was not concurrent-safe). A backpatch could be revisited in the future. This is the second time this change is attempted, ccfbd92 being the first one, but this time no assertions are added for the case of a TLI history file written concurrently by the WAL receiver or the startup process because we can expect one to exist (some of the TAP tests are able to trigger with a proper timing). Author: Nathan Bossart Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13 Discussion: https://postgr.es/m/Ym6GZbqQdlalSKSG@paquier.xyz	4 years ago
Tom Lane	23e7b38bfe	Pre-beta mechanical code beautification. ... Run pgindent, pgperltidy, and reformat-dat-files. I manually fixed a couple of comments that pgindent uglified.	4 years ago
Michael Paquier	55b5686511	Revert recent changes with durable_rename_excl() ... This reverts commits 2c902bb and ccfbd92. Per buildfarm members kestrel, rorqual and calliphoridae, the assertions checking that a TLI history file should not exist when created by a WAL receiver have been failing, and switching to durable_rename() over durable_rename_excl() would cause the newest TLI history file to overwrite the existing one. We need to think harder about such cases, so revert the new logic for now. Note that all the failures have been reported in the test 025_stuck_on_old_timeline. Discussion: https://postgr.es/m/511362.1651116498@sss.pgh.pa.us	4 years ago
Michael Paquier	ccfbd9287d	Replace existing durable_rename_excl() calls with durable_rename() ... durable_rename_excl() attempts to avoid overwriting any existing files by using link() and unlink(), falling back to rename() on some platforms (e.g., Windows where link() followed by unlink() is not concurrent-safe, see 909b449). Most callers of durable_rename_excl() use it just in case there is an existing file, but it happens that for all of them we never expect a target file to exist (WAL segment recycling, creation of timeline history file and basic_archive). basic_archive used durable_rename_excl() to avoid overwriting an archive concurrently created by another server. Now, there is a stat() call to avoid overwriting an existing archive a couple of lines above, so note that this change opens a small TOCTOU window in this module between the stat() call and durable_rename(). Furthermore, as mentioned in the top comment of durable_rename_excl(), this routine can result in multiple hard links to the same file and data corruption, with two or more links to the same file in pg_wal/ if a crash happens before the unlink() call during WAL recycling. Specifically, this would produce links to the same file for the current WAL file and the next one because the half-recycled WAL file was re-recycled during crash recovery of a follow-up cluster restart. 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 all those code paths never expect an existing file (a couple of assertions are added to check after that, in case). This is a bug fix, but knowing the unlikeliness of the problem involving one of more crashes at an exceptionally bad moment, no backpatch is done. This could be revisited in the future. Author: Nathan Bossart Reviewed-by: Robert Haas, Kyotaro Horiguchi, Michael Paquier Discussion: https://postgr.es/m/20220407182954.GA1231544@nathanxps13	4 years ago
Tom Lane	88103567cb	Disallow setting bogus GUCs within an extension's reserved namespace. ... Commit 75d22069e tried to throw a warning for setting a custom GUC whose prefix belongs to a previously-loaded extension, if there is no such GUC defined by the extension. But that caused unstable behavior with parallel workers, because workers don't necessarily load extensions and GUCs in the same order their leader did. To make that work safely, we have to completely disallow the case. We now actually remove any such GUCs at the time of initial extension load, and then throw an error not just a warning if you try to add one later. While this might create a compatibility issue for a few people, the improvement in error-detection capability seems worth it; it's hard to believe that there's any good use-case for choosing such GUC names. This also un-reverts 5609cc01c (Rename EmitWarningsOnPlaceholders() to MarkGUCPrefixReserved()), since that function's old name is now even more of a misnomer. Florin Irion and Tom Lane Discussion: https://postgr.es/m/1902182.1640711215@sss.pgh.pa.us	4 years ago
Robert Haas	5ef1eefd76	Allow archiving via loadable modules. ... Running a shell command for each file to be archived has a lot of overhead and may not offer as much error checking as you want, or the exact semantics that you want. So, offer the option to call a loadable module for each file to be archived, rather than running a shell command. Also, add a 'basic_archive' contrib module as an example implementation that archives to a local directory. Nathan Bossart, with a little bit of kibitzing by me. Discussion: http://postgr.es/m/20220202224433.GA1036711@nathanxps13	4 years ago