Re: Simplify standby state machine a bit in WaitForWALToBecomeAvailable()

On Tue, Oct 18, 2022 at 12:01 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> Hi,
>
> In standby mode, the state machine in WaitForWALToBecomeAvailable()
> reads WAL from pg_wal after failing to read from the archive. This is
> currently implemented in XLogFileReadAnyTLI() by calling
> XLogFileRead() with source XLOG_FROM_PG_WAL after it fails with source
> XLOG_FROM_PG_ARCHIVE and the current source isn't changed at all.
> Also, passing the source to XLogFileReadAnyTLI() in
> WaitForWALToBecomeAvailable() isn't straight i.e. it's not necessary
> to pass in XLOG_FROM_ANY at all. These things make the state machine a
> bit complicated and hard to understand.
>
> The attached patch attempts to simplify the code a bit by changing the
> current source to XLOG_FROM_PG_WAL after failing in
> XLOG_FROM_PG_ARCHIVE so that the state machine can move smoothly to
> read from pg_wal. And we can just pass the current source to
> XLogFileReadAnyTLI(). It also enables us to reduce a bit of extra
> XLogFileRead() code in XLogFileReadAnyTLI().
>
> Thoughts?

+1

Regards,
Amul