I don't fully understand the xlog files or WAL records but... Why isn't the writing of the WAL record based on the CACHE value of the sequence? If a request to nextval() can't be satisfied by the cache, the sequence on disk should be updated resulting in a WAL record being written.
If two sessions are accessing the sequence, they will likely end up not writing sequential values as they have both taken a chunk of values by calling nextval() but the effect of this could be controlled by the user by selecting an acceptable value for CACHE. If I don't mind having session 1 write records 1-10 while session 2 interleaves those with records 11-20, I should set my cache to 10. If I want my id's to map to insertion time as closely as possible I should set the cache lower (or NOCACHE, is that an option?). I'm concerned that the discussion here has been of the opinion that since no records were written to the database using the value retrieved from the sequence that no damage has been done. We are using database sequences to get unique identifiers for things outside the database. If a sequence could ever under any circumstances reissue a value, this could be damaging to the integrity of our software. ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/users-lounge/docs/faq.html
