Horton

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

Euler Taveira <euler@eulerto.com>

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From: "Euler Taveira" <euler@eulerto.com>
To: "Alexander Korotkov" <aekorotkov@gmail.com>
Cc: "Thomas Munro" <thomas.munro@gmail.com>, "Kartyshov Ivan" <i.kartyshov@postgrespro.ru>, "Bharath Rupireddy" <bharath.rupireddyforpostgres@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: 2024-03-29T16:50:33Z
Lists: pgsql-hackers 
On Fri, Mar 29, 2024, at 9:44 AM, Alexander Korotkov wrote:
> This generally makes sense, but I'm not sure about this.  The
> milliseconds timeout was used initially but received critics in [1].

Alexander, I see why you changed the patch.

Peter suggested to use an interval but you proposed another data type:
float. The advantage of the interval data type is that you don't need to
carefully think about the unit, however, if you use the integer data
type you have to propose one. (If that's the case, milliseconds is a
good granularity for this feature.) I don't have a strong preference
between integer and interval data types but I don't like the float for
this case. The 2 main reasons are (a) that we treat time units (hours,
minutes, seconds, ...) as integers so it seems natural for a human being
to use a unit time as integer and (b) depending on the number of digits
after the decimal separator you still don't have an integer in the
internal unit, hence, you have to round it to integer.

We already have functions that use integer (such as pg_terminate_backend)
and interval (such as pg_sleep_for) and if i searched correctly it will
be the first timeout argument as float.


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

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