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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