How to read some values reported by pgmetrics (e.g. shared_buffers, max_wal_size) about pgmetrics HOT 6 CLOSED

Saw this and realised I could help.

shared_buffers without units is specified in blocks, typically 8kB – docs

max_wal_size without units is specified in segment files, typically 16MB – docs

from pgmetrics.

Yes, @mchristofides is correct. pgmetrics is showing the literal value in defined units of the setting, and in paranthesis, the effective value in bytes. In the line:

|                  shared_buffers |  524288 (4.0 GiB) |

it is trying to say that the value is 524288 blocks, which means 4.0 GB since each block is of size 8192 bytes.

from pgmetrics.

Thanks @mchristofides and @mdevan. So I'm OK with shared_buffers as 524288 blocks (4.0 GiB) is consistent with my settings. Maybe a default blocks unit would be worth but pgmetrics is ok, let's say it's and enhancement request.

Now, I understand max_wal_size and pgmetrics seems wrong on the left figure misinterpreting the default unit as 16MB, one should read 2048 (MB) (4 GiB) and not 2048 (16MB) (32 GiB) to be consistent with my settings. In that case it's closer to a bug maybe.

from pgmetrics.

Hmm, yes, you're right, there is a bug here.

For Postgres 9.4 and below, the setting was called checkpoint_segments (as the number of segments, unitless). For 9.5 and 9.6 the setting is max_wal_size with a unit of 16MB and for 10 and above it is max_wal_size with a unit of 1MB.

pgmetrics reporting code assumes 16MB for 9.5+, it does not use 1MB for 10+. Are you using Postgres 10 or above?

Will fix.

from pgmetrics.

For this specific case, it's PostgreSQL 12 indeed.

from pgmetrics.

Fixed in 513dcc0. Thanks for reporting.

from pgmetrics.