Horton

Re: LogwrtResult contended spinlock

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, pgsql-hackers@lists.postgresql.org, Jaime Casanova <jcasanov@systemguards.com.ec>
Date: 2024-04-03T12:00:09Z
Lists: pgsql-hackers 
On 2024-Apr-03, Alvaro Herrera wrote:

> So what I do in the attached 0001 is stop using the XLogwrtResult struct
> in XLogCtl and replace it with separate Write and Flush values, and add
> the macro XLogUpdateLocalLogwrtResult() that copies the values of Write
> and Flush from the shared XLogCtl to the local variable given as macro
> argument.  (I also added our idiomatic do {} while(0) to the macro
> definition, for safety).  The new members are XLogCtl->logWriteResult
> and XLogCtl->logFlushResult and as of 0001 are just XLogRecPtr, so
> essentially identical semantics as the previous code.  No atomic access
> yet!

BTW I forgot.  I didn't like the name XLogUpdateLocalLogwrtResult() name
much.  What do you think about RefreshXLogWriteResult() instead?

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"How strange it is to find the words "Perl" and "saner" in such close
proximity, with no apparent sense of irony. I doubt that Larry himself
could have managed it."         (ncm, http://lwn.net/Articles/174769/)

Commits

  1. Remove bogus assertion in pg_atomic_monotonic_advance_u64

  2. Add XLogCtl->logInsertResult

  3. Operate XLogCtl->log{Write,Flush}Result with atomics

  4. Split XLogCtl->LogwrtResult into separate struct members

  5. Introduce atomic read/write functions with full barrier semantics.

  6. Reduce the number of GetFlushRecPtr() calls done by walsenders.

  7. Remove most volatile qualifiers from xlog.c