From mboxrd@z Thu Jan  1 00:00:00 1970
From: Loic Dachary <loic@dachary.org>
Subject: rationale for a PGLog::merge_old_entry case
Date: Sun, 02 Jun 2013 13:09:55 +0200
Message-ID: <51AB2803.9010807@dachary.org>
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To: Samuel Just <sam.just@inktank.com>
Cc: Ceph Development <ceph-devel@vger.kernel.org>

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Hi Sam,

TL;DR:

When there no new entry, what is the rationale for merge_old_entry to rem=
ove the object from missing only if the tail is eversion_t() and the obje=
ct prior_version is also eversion_t() ?
https://github.com/dachary/ceph/blob/f58299db098d5f18c817b516fa6ffaa76245=
e57d/src/osd/PGLog.cc#L330

Long version:

The conditions are created with:

    info.log_tail =3D eversion_t();
    oe.soid.hash =3D 1;
    oe.op =3D pg_log_entry_t::DELETE;
    oe.prior_version =3D eversion_t();
   =20
    missing.add(oe.soid, eversion_t(1,1), eversion_t());

as shown in
https://github.com/dachary/ceph/blob/f58299db098d5f18c817b516fa6ffaa76245=
e57d/src/test/osd/TestPGLog.cc#L467
I double checked with gdb and when called with

EXPECT_FALSE(merge_old_entry(t, oe, info, remove_snap, dirty_log));
https://github.com/dachary/ceph/blob/f58299db098d5f18c817b516fa6ffaa76245=
e57d/src/test/osd/TestPGLog.cc#L481

it reaches

missing.rm(oe.soid, missing.missing[oe.soid].need);
https://github.com/dachary/ceph/blob/f58299db098d5f18c817b516fa6ffaa76245=
e57d/src/osd/PGLog.cc#L330

and the expected side effects are observed:

    EXPECT_FALSE(dirty_log);
    EXPECT_TRUE(remove_snap.empty());
    EXPECT_TRUE(t.empty());
    EXPECT_FALSE(missing.have_missing());
    EXPECT_TRUE(log.empty());
    EXPECT_EQ(0U, ondisklog.length());
https://github.com/dachary/ceph/blob/f58299db098d5f18c817b516fa6ffaa76245=
e57d/src/test/osd/TestPGLog.cc#L483

Cheers

--=20
Lo=EFc Dachary, Artisan Logiciel Libre
All that is necessary for the triumph of evil is that good people do noth=
ing.


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