Horton

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

Andy Fan <zhihuifan1213@163.com>

View thread View on postgr.es
From: Andy Fan <zhihuifan1213@163.com>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Kartyshov Ivan <i.kartyshov@postgrespro.ru>, Euler Taveira <euler@eulerto.com>, Thomas Munro <thomas.munro@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Amit Kapila <amit.kapila16@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2024-04-02T08:14:49Z
Lists: pgsql-hackers 
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

Commits

  1. Ensure standby promotion point in 043_wal_replay_wait.pl

  2. Minor cleanup related to pg_wal_replay_wait() procedure

  3. Adjust pg_wal_replay_wait() procedure behavior on promoted standby

  4. pg_wal_replay_wait(): Fix typo in the doc

  5. Implement pg_wal_replay_wait() stored procedure

  6. Revert: Implement pg_wal_replay_wait() stored procedure

  7. Call WaitLSNCleanup() in AbortTransaction()

  8. Clarify what is protected by WaitLSNLock

  9. Use an LWLock instead of a spinlock in waitlsn.c

  10. Use the pairing heap instead of a flat array for LSN replay waiters

  11. Minor improvements for waitlsn.c

  12. Make the order of the header file includes consistent