feat(wal): add restore mode to WALRestoreRequest#351
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The operator can now tell WAL restore plugins whether a WAL file is being restored by an instance in recovery or on behalf of pg_rewind, which requires fetching exactly the requested file, without WAL prefetching and without caching archive misses observed on nearby segments. Signed-off-by: Armando Ruocco <armando.ruocco@enterprisedb.com>
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The operator now tells WAL restore plugins when a restore request is made on behalf of pg_rewind (cloudnative-pg/cnpg-i#351). pg_rewind walks the timeline backwards, fetches every WAL file it needs exactly once, and treats any restore failure as fatal, so both optimizations meant for an instance in recovery must stay off: prefetching the following segments is wasted work that ends in an archive miss, and the end-of-wal-stream flag recorded by such a miss makes a later invocation fail on a segment that is available in the archive, aborting the whole rewind. The cnpg-i dependency points to a pseudo-version of that pull request and will be moved to the next tagged release once it is available. Ref: cloudnative-pg/cloudnative-pg#11200 Signed-off-by: Armando Ruocco <armando.ruocco@enterprisedb.com>
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The operator now tells WAL restore plugins when a restore request is made on behalf of pg_rewind (cloudnative-pg/cnpg-i#351). pg_rewind walks the timeline backwards, fetches every WAL file it needs exactly once, and treats any restore failure as fatal, so both optimizations meant for an instance in recovery must stay off: prefetching the following segments is wasted work that ends in an archive miss, and the end-of-wal-stream flag recorded by such a miss makes a later invocation fail on a segment that is available in the archive, aborting the whole rewind. The cnpg-i dependency points to a pseudo-version of that pull request and will be moved to the next tagged release once it is available. Ref: cloudnative-pg/cloudnative-pg#11200 Signed-off-by: Armando Ruocco <armando.ruocco@enterprisedb.com>
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pg_rewind fetches the WAL files it needs by running the cluster's
restore_command, and when WAL restore is handled by a plugin those invocations reach the plugin with no way to tell that pg_rewind, and not an instance in recovery, is asking. The difference matters: pg_rewind walks the timeline backwards, fetches every file exactly once, and treats any restore failure as fatal, so the optimizations a plugin applies during recovery, like prefetching the following segments or caching an archive miss to signal the end of the WAL stream, actively break it. cloudnative-pg/cloudnative-pg#11200 shows the resulting failure on the in-tree restore path, fixed by cloudnative-pg/cloudnative-pg#11204; plugins need this field to do the same.WALRestoreRequestgains amodefield stating the context the WAL file is being restored in.MODE_REWINDasks the plugin to retrieve exactly the requested file, without prefetching and without caching archive misses.MODE_UNSPECIFIEDis what an operator predating the field sends and must be read asMODE_RECOVERY. The field is optional, so older operators and older plugins keep their current behavior.Part of cloudnative-pg/cloudnative-pg#11200.