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doc: erasure code ghobject is made of gen_t + shard_t

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Signed-off-by: Loic Dachary <loic@dachary.org>
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Loic Dachary 2013-08-28 23:04:26 +02:00
parent d9187a73c3
commit 3c9f8498c8
1 changed files with 13 additions and 10 deletions
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23
doc/dev/osd_internals/erasure_coding/pgbackend.rst
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@ -79,10 +79,13 @@ Core Changes:
APPEND, DELETE, (SET|RM)ATTR log entries.
- The filestore needs to be able to deal with multiply versioned
hobjects. This probably means adapting the filestore internally to
use a vhobject which is basically a pair<version_t, hobject_t>. The
version needs to be included in the on-disk filename. An interface
needs to be added to get all versions of a particular hobject_t or
the most recently versioned instance of a particular hobject_t.
use a ghobject which is basically a tuple<hobject_t, gen_t,
shard_t>. The gen_t + shard_t need to be included in the on-disk
filename. gen_t is a unique object identifier to make sure there
are no name collisions when object N is created +
deleted + created again. An interface needs to be added to get all
versions of a particular hobject_t or the most recently versioned
instance of a particular hobject_t.
PGBackend Interfaces:
@ -178,7 +181,7 @@ acting set have different pieces of the erasure coding scheme and are
not interchangeable. Worse, crush might cause chunk 2 to be written
to an osd which happens already to contain an (old) copy of chunk 4.
This means that the OSD and PG messages need to work in terms of a
type like pair<chunk_id_t, pg_t> in order to distinguish different pg
type like pair<shard_t, pg_t> in order to distinguish different pg
chunks on a single OSD.
Because the mapping of object name to object in the filestore must
@ -188,14 +191,14 @@ include the chunk id in the object key.
Core changes:
- The filestore `vhobject_t needs to also include a chunk id
- The filestore `ghobject_t needs to also include a chunk id
<http://tracker.ceph.com/issues/5862>`_ making it more like
tuple<hobject_t, version_t, chunk_id_t>.
- coll_t needs to include a chunk_id_t.
tuple<hobject_t, gen_t, shard_t>.
- coll_t needs to include a shard_t.
- The `OSD pg_map and similar pg mappings need to work in terms of a
cpg_t <http://tracker.ceph.com/issues/5863>`_ (essentially
pair<pg_t, chunk_id_t>). Similarly, pg->pg messages need to include
a chunk_id_t
pair<pg_t, shard_t>). Similarly, pg->pg messages need to include
a shard_t
- For client->PG messages, the OSD will need a way to know which PG
chunk should get the message since the OSD may contain both a
primary and non-primary chunk for the same pg