[tarantool-patches] Re: [PATCH 1/7] Refactoring: wal writer fiber and queue

[Konstantin Osipov]

* Georgy Kirichenko <georgy at tarantool.org> [19/08/13 10:30]:
> As wal processes all writes in a cbus loop fiber it isn't possible to
> yield while write. The patch introduces a wal write queue and a wal write
> fiber which fetch a batch from queue and writes it out. Also checkpoint
> requests are going now throw the queue to synchronize a tx checkpoint
though 
> status with wal.

I don't understand this patch.

First, WAL already runs in a fiber, and you can yield.

cord_costart creates a new fiber, please check out the implementation.

this is done by this commit:

    commit f4625e64eb99c17910d3f0bcd323e5d82b6d5b31
    Author: Vladimir Davydov <vdavydov.dev at gmail.com>
    Date:   Wed Jul 4 20:20:55 2018 +0300

    vinyl: use cbus for communication between scheduler and worker threads

    We need cbus for forwarding deferred DELETE statements generated in a
    worker thread during primary index compaction to the tx thread where
    they can be inserted into secondary indexes. Since pthread mutex/cond
    and cbus are incompatible by their nature, let's rework communication
    channel between the tx and worker threads using cbus.

    Needed for #2129

Check out the commit, it changes cord_start() to cord_costart().


Second, checkpoint message already flushed the queue. So I don't
understand why you need a switch over message type.

Let's discuss online.


-- 
Konstantin Osipov, Moscow, Russia