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

On Tue, Feb 28, 2023 at 10:38 AM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
+/*
+ * Guts of XLogReadFromBuffers().
+ *
+ * Read 'count' bytes into 'buf', starting at location 'ptr', from WAL
+ * fetched WAL buffers on timeline 'tli' and return the read bytes.
+ */
s/fetched WAL buffers/fetched from WAL buffers

+ else if (nread < nbytes)
+ {
+ /*
+ * We read some of the requested bytes. Continue to read remaining
+ * bytes.
+ */
+ ptr += nread;
+ nbytes -= nread;
+ dst += nread;
+ *read_bytes += nread;
+ }

The 'if' condition should always be true. You can replace the same
with an assertion instead.
s/Continue to read remaining/Continue to read the remaining

The good thing about this patch is that it reduces read IO calls
without impacting the write performance (at least not that
noticeable). It also takes us one step forward towards the
enhancements mentioned in the thread. If performance is a concern, we
can introduce a GUC to enable/disable this feature.

--
Thanks & Regards,
Kuntal Ghosh