Re: pg_wal_lsn_diff

Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp> writes:
> According to the pg_wal_lsn_diff manual:
> pg_wal_lsn_diff ( lsn pg_lsn, lsn pg_lsn ) $B"*(B numeric

> Calculates the difference in bytes between two write-ahead log
> locations. This can be used with pg_stat_replication or some of
> the functions shown in Table 9.87 to get the replication lag.

> It's not clear whether its return value is (first arg - second arg) or
> (second arg - first arg). The order matters because the return value
> could have a sign (it actually does first arg - second arg). Attached
> is a patch to fix the description.

+1 for fixing that. Two notes though: first, your text doesn't agree
with the prototype ("ls1" should be "lsn1"), and second, I think it
would read better if you didn't split the phrase "difference in bytes".
That is,

- Calculates the difference in bytes between two write-ahead log
+ Calculates the difference in bytes (lsn1 - lsn2) between two write-ahead log

Also maybe you should use the <parameter>lsn1</parameter> markup
in the text.

regards, tom lane