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

Hi Alexander!

>> + </indexterm>
>> + <function>pg_wal_replay_wait</function> (
>> + <parameter>target_lsn</parameter> <type>pg_lsn</type>,
>> + <parameter>timeout</parameter> <type>bigint</type> <literal>DEFAULT</literal> <literal>0</literal>)
>> + <returnvalue>void</returnvalue>
>> + </para>
>>
>> Should we return the millseconds of waiting time? I think this
>> information may be useful for customer if they want to know how long
>> time it waits for for minitor purpose.
>
> Please, check it more carefully. In v17 timeout is in integer milliseconds.

I guess one of us misunderstand the other:( and I do didn't check the
code very carefully.

Acutally I meant the "return value" rather than function argument. IIUC
the current return value is void per below statement.

>> + <returnvalue>void</returnvalue>

If so, when users call pg_wal_replay_wait, they can get informed when
the wal is replaied to the target_lsn, but they can't know how long time
it waits unless they check it in application side, I think such
information will be useful for monitor purpose sometimes.

select pg_wal_replay_wait(lsn, 1000); may just take 1ms in fact, in
this case, I want this function return 1.

--
Best Regards
Andy Fan