mirror of
https://github.com/ceph/ceph
synced 2024-12-09 13:08:28 +00:00
f6151f7697
Signed-off-by: Sage Weil <sage@redhat.com>
86 lines
3.4 KiB
ReStructuredText
86 lines
3.4 KiB
ReStructuredText
===================
|
|
BlueStore Internals
|
|
===================
|
|
|
|
|
|
Small write strategies
|
|
----------------------
|
|
|
|
* *U*: Uncompressed write of a complete, new blob.
|
|
|
|
- write to new blob
|
|
- kv commit
|
|
|
|
* *P*: Uncompressed partial write to unused region of an existing
|
|
blob.
|
|
|
|
- write to unused chunk(s) of existing blob
|
|
- kv commit
|
|
|
|
* *W*: WAL overwrite: commit intent to overwrite, then overwrite
|
|
async. Must be chunk_size = MAX(block_size, csum_block_size)
|
|
aligned.
|
|
|
|
- kv commit
|
|
- wal overwrite (chunk-aligned) of existing blob
|
|
|
|
* *N*: Uncompressed partial write to a new blob. Initially sparsely
|
|
utilized. Future writes will either be *P* or *W*.
|
|
|
|
- write into a new (sparse) blob
|
|
- kv commit
|
|
|
|
* *R+W*: Read partial chunk, then to WAL overwrite.
|
|
|
|
- read (out to chunk boundaries)
|
|
- kv commit
|
|
- wal overwrite (chunk-aligned) of existing blob
|
|
|
|
* *C*: Compress data, write to new blob.
|
|
|
|
- compress and write to new blob
|
|
- kv commit
|
|
|
|
Possible future modes
|
|
---------------------
|
|
|
|
* *F*: Fragment lextent space by writing small piece of data into a
|
|
piecemeal blob (that collects random, noncontiguous bits of data we
|
|
need to write).
|
|
|
|
- write to a piecemeal blob (min_alloc_size or larger, but we use just one block of it)
|
|
- kv commit
|
|
|
|
* *X*: WAL read/modify/write on a single block (like legacy
|
|
bluestore). No checksum.
|
|
|
|
- kv commit
|
|
- wal read/modify/write
|
|
|
|
Mapping
|
|
-------
|
|
|
|
This very roughly maps the type of write onto what we do when we
|
|
encounter a given blob. In practice it's a bit more complicated since there
|
|
might be several blobs to consider (e.g., we might be able to *W* into one or
|
|
*P* into another), but it should communicate a rough idea of strategy.
|
|
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| | raw | raw (cached) | csum (4 KB) | csum (16 KB) | comp (128 KB) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 128+ KB (over)write | U | U | U | U | C |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 64 KB (over)write | U | U | U | U | U or C |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 4 KB overwrite | W | P | W | P | W | P | R+W | P | N (F?) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 100 byte overwrite | R+W | P | W | P | R+W | P | R+W | P | N (F?) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 100 byte append | R+W | P | W | P | R+W | P | R+W | P | N (F?) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 4 KB clone overwrite | P | N | P | N | P | N | P | N | N (F?) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|
|
| 100 byte clone overwrite | P | N | P | N | P | N | P | N | N (F?) |
|
|
+--------------------------+--------+--------------+-------------+--------------+---------------+
|