I took another look at this patch, and I think it's ready to go in, it clearly fixes a bug that isn't too hard to hit in production settings. To ensure we don't break this I've added a testcase which pipes the pg_rewind --verbose output to a file it's asked to copy, which then guarantees that the file is growing in size during the operation without need for synchronizing two processes with IPC::Run (it also passes on Windows in the CI setup).
One small comment on the patch: + snprintf(srcpath, sizeof(srcpath), "%s/%s", datadir, path); This should IMO check the returnvalue of snprintf to ensure it wasn't truncated. While the risk is exceedingly small, a truncated filename might match another existing filename and the error not getting caught. There is another instance just like this one in open_target_file() to which I think we should apply the same belts-and-suspenders treatment. I've fixed this in the attached version which also have had a pg_indent run on top of a fresh rebase. Thoughts on this version? -- Daniel Gustafsson https://vmware.com/
v3-0001-pg_rewind-Fetch-small-files-according-to-new-size.patch
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