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d09f765b9d
The previous method for doing that was to write zeroes into a predetermined set of page locations. However, there's a roughly 1-in-64K chance that the existing checksum will match by chance, and yesterday several buildfarm animals started to reproducibly see that, resulting in test failures because no checksum mismatch was reported. Since the checksum includes the page LSN, test success depends on the length of the installation's WAL history, which is affected by (at least) the initial catalog contents, the set of locales installed on the system, and the length of the pathname of the test directory. Sooner or later we were going to hit a chance match, and today is that day. Harden these tests by specifically inverting the checksum field and leaving all else alone, thereby guaranteeing that the checksum is incorrect. In passing, fix places that were using seek() to set up for syswrite(), a combination that the Perl docs very explicitly warn against. We've probably escaped problems because no regular buffered I/O is done on these filehandles; but if it ever breaks, we wouldn't deserve or get much sympathy. Although we've only seen problems in HEAD, now that we recognize the environmental dependencies it seems like it might be just a matter of time until someone manages to hit this in back-branch testing. Hence, back-patch to v11 where we started doing this kind of test. Discussion: https://postgr.es/m/3192026.1648185780@sss.pgh.pa.us |
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