Comment 13 for bug 1692775

Reviewed: https://review.openstack.org/518311
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=41754fd57f27bba646d1d6e26388c7f5f4c2dc4e
Submitter: Zuul
Branch: driverfixes/newton

commit 41754fd57f27bba646d1d6e26388c7f5f4c2dc4e
Author: Gorka Eguileor <email address hidden>
Date: Wed Sep 13 19:46:17 2017 +0200

    Run backup compression on native thread

    Backup data compression is a CPU bound operation that will not yield to
    other greenthreads, so given enough simultaneous backup operations they
    will lead to other threads' starvation.

    This is really problematic for DB connections, since starvation will
    lead to connections getting dropped with errors such as "Lost connection
    to MySQL server during query".

    Detailed information on why these connections get dropped can be found
    in comment "[31 Aug 2007 9:21] Magnus Blåudd" on this MySQL bug [1].

    These DB issues may result in backups unnecessary ending in an "error"
    state.

    This patch fixes this by moving the compression to a native thread so
    the cooperative multitasking in Cinder Backup can continue switching
    threads.

    [1] https://bugs.mysql.com/bug.php?id=28359

    Closes-Bug: #1692775
    Closes-Bug: #1719580
    Change-Id: I1946dc0ad9cb7a68072a39816fa9fa224c2eb6a5
    (cherry picked from commit af0f00bc52f79d9395adfe0575b0dbe353e18bbe)
    (cherry picked from commit 439f90da8e4c1cfa1acfe36b5ea8a6c5bae6139f)
    (cherry picked from commit b241f93267646a6501e3a5fb14521f05e38a2ae9)