Re: [HACKERS] make async slave to wait for lsn to be replayed

On Thu, Mar 28, 2024, at 9:39 AM, Alexander Korotkov wrote:
> Fixed along with other issues spotted by Alexander Lakhin.

[I didn't read the whole thread. I'm sorry if I missed something ...]

You renamed the function in a previous version but let me suggest another one:
pg_wal_replay_wait. It uses the same pattern as the other recovery control
functions [1]. I think "for" doesn't add much for the function name and "lsn" is
used in functions that return an LSN (that's not the case here).

postgres=# \df pg_wal_replay*
List of functions
-[ RECORD 1 ]-------+---------------------
Schema | pg_catalog
Name | pg_wal_replay_pause
Result data type | void
Argument data types |
Type | func
-[ RECORD 2 ]-------+---------------------
Schema | pg_catalog
Name | pg_wal_replay_resume
Result data type | void
Argument data types |
Type | func

Regarding the arguments, I think the timeout should be bigint. There is at least
another function that implements a timeout that uses bigint.

postgres=# \df pg_terminate_backend
List of functions
-[ RECORD 1 ]-------+--------------------------------------
Schema | pg_catalog
Name | pg_terminate_backend
Result data type | boolean
Argument data types | pid integer, timeout bigint DEFAULT 0
Type | func

I also suggests that the timeout unit should be milliseconds, hence, using
bigint is perfectly fine for the timeout argument.

+ <para>
+ Throws an ERROR if the target <acronym>lsn</acronym> was not replayed
+ on standby within given timeout. Parameter <parameter>timeout</parameter>
+ is the time in seconds to wait for the <parameter>target_lsn</parameter>
+ replay. When <parameter>timeout</parameter> value equals to zero no
+ timeout is applied.
+ </para></entry>

[1] https://www.postgresql.org/docs/current/functions-admin.html#FUNCTIONS-RECOVERY-CONTROL

--
Euler Taveira
EDB https://www.enterprisedb.com/