Re: [Tarantool-patches] [PATCH] recovery: make it yield when positioning in a WAL

[Vladislav Shpilevoy via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi! Thanks for the patch!

Technically looks good now, can be pushed.

But in case you would find it interesting: now relay->row_count looks odd.
Because its comment is not very correct, most of that is moved to the
recovery layer. And because it is used only by initial join. And because we
still have a single place where we use xstream/recovery, but the yields
are not managed by them.

Did you think about moving your code to xstream instead of recovery? Then
it would be truly not related to recovery. It would have 2 methods:

- write(struct xstream *, struct xrow_header *)
- skip(struct xstream *, struct xrow_header *)

Recovery calls skip() while establishes a position, for each skipped row.
Relaying from memory never calls skip, but calls only write() like now.

In order to yield you inherit xtream, add a member row_count, and both in
skip() and write() increment it like you do. And then yield periodically.

It would work for the initial join too.

Or add row_count right to the xtream struct, and replace skip() with your
function schedule_yield(). This way row_count would be visible to recovery
and available for reporting in the logs like '... rows recovered'. And we
wouldn't all too many virtual functions for the skipped rows.

All that up to you.