Use WALReadFromBuffers in more places

Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

To: PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2024-04-24T16:08:57Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Read WAL directly from WAL buffers.
- 91f2cae7a4e6 17.0 cited

Attachments

v1-0001-Use-WALReadFromBuffers-in-more-places.patch (application/octet-stream) patch v1-0001
v1-0002-Add-test-module-to-demonstrate-reading-from-WAL-b.patch (application/octet-stream) patch v1-0002

Hi,

Commit 91f2cae7a4e that introduced WALReadFromBuffers only used it for
physical walsenders. It can also be used in more places benefitting
logical walsenders, backends running pg_walinspect and logical
decoding functions if the WAL is available in WAL buffers. I'm
attaching a 0001 patch for this.

While at it, I've also added a test module in 0002 patch to
demonstrate 2 things: 1) how the caller can ensure the requested WAL
is fully copied to WAL buffers using WaitXLogInsertionsToFinish before
reading from WAL buffers. 2) how one can implement an xlogreader
page_read callback to read unflushed/not-yet-flushed WAL directly from
WAL buffers. FWIW, a separate test module to explicitly test the new
function is suggested here -
https://www.postgresql.org/message-id/CAFiTN-sE7CJn-ZFj%2B-0Wv6TNytv_fp4n%2BeCszspxJ3mt77t5ig%40mail.gmail.com.

Please have a look at the attached patches.

I will register this for the next commit fest.

-- 
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com