Commit 91f2cae7a4e that introduced WALReadFromBuffers only used it for physical walsenders. It can also be used in more places benefitting logical walsenders, backends running pg_walinspect and logical decoding functions if the WAL is available in WAL buffers. I'm attaching a 0001 patch for this.
Thank you for working on this. It seems like a useful optimization. Do you have any information on how much this improves the performance of the new callers of WALReadFromBuffers?
Regarding the v3 version of the patch, do you also intend to include other callers of WALRead,
such as walsummarizer.c and pg_waldump.c?
In WALReadFromBuffers, the buffer scan currently stops when it encounters a buffer that
doesn't have the needed WAL page. However, it's possible to continue scanning past the missing page and find other relevant pages further along. By keeping track of which pages are missing, we could read only those specific pages from files, instead of reading everything after the first missing page. I am wondering if this was taken into account during the design of the function.
