undefined | Better HN

0 pointsThaxll6y ago0 comments

No PG does not fsync every writes, more details here: https://dba.stackexchange.com/questions/254069/how-often-doe...

My point is people complain about MongoDB are the one not using it most likely, MongoDB is very different from 10 years ago.

I like to remind people that PG did not have an official replication system 10years ago and as of today is still behind MySQL. No DB is perfect, it's about tradeof.

0 comments

wolf550e6y ago

> It writes out and syncs the accumulated WAL records at each transaction commit, unless the committed transaction touched only UNLOGGED or TEMP tables, or synchronous_commit is turned off.

So wal is synced before commit returns, and if you power cycle immediately after, the wal is played back and your transaction is not lost? So it's fine?

It does not need to sync all writes, only the records needed to play back the transaction after restart. This is what all real databases do.

robocat6y ago

“PG writes out and syncs the accumulated WAL (= Transaction log) records at each transaction commit [snip] It also syncs at the end of each WAL file (16MB by default). The wal_writer process also wakes up occasionally and writes out and syncs the WAL.“

So PG keeps data consistent by default - unlike MongoDB.

> MySQL and PG are not truly consistent per default, they don't fsync every writes. MongoDB explains that pretty well [links]

Where in those MongoDB doc links is there anything about MySQL or PG?

j / k navigate · click thread line to collapse