News for hackers. Stuff that matters.

A comment on PostgreSQL used fsync incorrectly for 20 years. Parent comment

Re:PostgreSQL used fsync incorrectly for 20 years by pgaddict on Sunday February 10, 2019 @12:47PM (#19128918)
> Well, but on-disk varlena data is included. pg_column_size() averages 144 bytes for pg_attribute on my system.

Sure, but I thought we're talking about in-memory stuff as you've been talking about tuple descriptors. I don't think the on-disk size matters all that much, TBH, it's likely just a tiny fraction of data stored in the cluster.

> I'm not sure that actually matters that much. Most attributes are allocated as part of TupleDescData, but that allocates all attributes together.

Ah. Good point.

[ Parent | on HN ]
Re:PostgreSQL used fsync incorrectly for 20 years by anarazel on Sunday February 10, 2019 @12:56PM (#19128980)
> I don't think the on-disk size matters all that much, TBH, it's likely just a tiny fraction of data stored in the cluster.

I've seen pg_attribute take up very significant fractions of the database numerous times, so I do think the on-disk size can matter. And there's plenty places, e.g. catcache, where we store the full on-disk tuple (rather than just the fixed-length prefix); so the on-disk size is actually quite relevant for the in-memory bit too.

[ Parent | on HN ]