References: 
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 <CAPpHfdu+HAF=XPX2v+Qq+faV2bVhj=qLz1TbtAZX5shg8Zviow@mail.gmail.com>
 <a7601ec6-01d8-4561-b81d-a6605e9b4d55@eisentraut.org>
 <CALj2ACV5+A2fRkMdB1YLH8tHMy8xsUr1HMu5RffJpmnfH-_42A@mail.gmail.com>
 <5358d911a08ef2952b1e9f74062426ee@postgrespro.ru>
 <CAPpHfdsQNqQoFN_OosMUkZWLE-s=or=t+XVEHF5AGuMbdBMpew@mail.gmail.com>
 <CAPpHfdvZXSiVCqFNMzpk7Zhxk4hB6T55b+79J1nKLotNFL25Qw@mail.gmail.com>
 <CA+hUKGKXXP8ZgTfFfjhv77ALC-ZKcejR4pdfrfgVqYrG_75zeQ@mail.gmail.com>
 <CAPpHfdv1aXn-oUQNODQ0B6W7JC=t_S1b64V5DAx-HP+KOV-6Lg@mail.gmail.com>
 <88449be3-93e8-4d78-a0d8-c37e4cf26850@app.fastmail.com>
 <CAPpHfduGLJgQERBmQ+=bsr4Oy6F8HCVgQpCYva6=Ncib2X2oUA@mail.gmail.com>
 <8aec133e-5d7f-4fa1-8223-257647dd1ccd@app.fastmail.com>
 <CAPpHfds7M2R0PLGzGa+Y6G+n1z1Na-t5QH2Wsv9iN3n=tcFyEw@mail.gmail.com>
 <432592e4d09341d41bf5cad1df26b3f3@postgrespro.ru>
 <CAPpHfdtmbUOfNWk_ofZyQWd5kztyXhCVmUHYcSr1-JuYO0DyUw@mail.gmail.com>
 <CALj2ACUhgYVHYH5JeNKro1v+SqmDcGyNHn0smWpsQMDLikrN=w@mail.gmail.com>
 <CAPpHfdsV856ca8V=G8DFEViDP7v1hMtDUgOEdBE5dV45a3NKKw@mail.gmail.com>
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 <CAPpHfdv4v-UrS90rSqp8wz9zsWpB7VB5bsPVAoETHWozkDwumA@mail.gmail.com>
User-agent: mu4e 1.10.7; emacs 29.1
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
Subject: Re: [HACKERS] make async slave to wait for lsn to be replayed
Date: Tue, 02 Apr 2024 16:14:49 +0800
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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