Re: Improve WALRead() to suck data directly from WAL buffers when possible

Nathan Bossart <nathandbossart@gmail.com>

From: Nathan Bossart <nathandbossart@gmail.com>

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

Cc: Dilip Kumar <dilipbalaut@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, pgsql-hackers@lists.postgresql.org

Date: 2023-02-28T00:44:52Z

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 →

Add XLogCtl->logInsertResult
- f3ff7bf83bce 17.0 cited
Add assert to WALReadFromBuffers().
- 9ecbf54075a9 17.0 landed
Read WAL directly from WAL buffers.
- 91f2cae7a4e6 17.0 landed
Additional write barrier in AdvanceXLInsertBuffer().
- 766571be1659 17.0 landed
Use 64-bit atomics for xlblocks array elements.
- c3a8e2a7cb16 17.0 landed
Don't trust unvalidated xl_tot_len.
- bae868caf222 17.0 cited

On Wed, Feb 08, 2023 at 08:00:00PM +0530, Bharath Rupireddy wrote:
> +			/*
> +			 * We read some of the requested bytes. Continue to read remaining
> +			 * bytes.
> +			 */
> +			ptr += nread;
> +			nbytes -= nread;
> +			dst += nread;
> +			*read_bytes += nread;

Why do we only read a page at a time in XLogReadFromBuffersGuts()?  What is
preventing us from copying all the data we need in one go?

-- 
Nathan Bossart
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