Hello Dan, so you are saying that if WAL is somehow in memory only (not properly persisted) and app or OS crashes in the middle of the checkpoint operation, my main database file will get corrupted? And by corrupted you mean as in "you will loose changes which were in the WAL file", or "you will end up with unusable main database file, or file where rows which were affected by the checkpoint will have wrong contents (halfway through written, ...)". In other words, I may end up with the main database file in some other state than just "like before checkpointing" or "like after checkpointing"? I understood checkpointing as a kind of atomic operation which "merges data in the main database file and in the WAL". Is that understanding wrong?

Thanks, Pavel


On 04/04/2018 06:33 PM, Dan Kennedy wrote:
On 04/04/2018 09:01 PM, Pavel Cernohorsky wrote:
Hello, does anybody know if there is some possibility to not have WAL file as a normal file on the disk, but only in memory? I understand that all the modifications to the database would get lost in case of the application / OS crash, but for my application, I only need the level of durability based on checkpointing. I just need to guarantee that all the data are properly written to the main database and synchronized to disk when manual (or even automatic) WAL checkpoint is called, but I do not care if I loose data in between the checkpoints. Of course database should never get corrupted.

If your app or the OS crashes halfway through a checkpoint and this means that the WAL file is lost, the database is likely to be corrupted. Is that a problem?

Dan.



My goal is to limit the number of IOps being performed to the disk. Currently I use "PRAGMA synchronous = 1" and there is only one process manipulating the database (multiple reader threads, only one writer thread at one moment in time). Or if it is not possible to have WAL in memory only, is there something like “PRAGMA wal_synchronous = none_and_delete_wal_if_corrupted”?

Thanks for suggestions, kind regards,
Pavel


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