Guys,
let me summarize what we decided regarding compression support in Ceph
during the Dev Meeting last week.
Below are possible implementation options, their pros/cons and the
conclusion.
1) Add compression support to RGW.
Pros/Cons:
+ Simple
+ Reduced inter-component traffic
- Limited to specific clients
- Will conflict with partial read/writes if any appear
Alyona Kiseleva from Mirantis (akyseleva@xxxxxxxxxxxx) will start
implementing this promptly. You can ask additional questions to her via
e-mail or during daily RGW stendups she is planning to attend regularly.
2) Add basic compression support to BlueStore. Basic = "Append only"
functionality to be implemented. Specific "append only" hint/flag needs
to be introduced for object creation interface.
Pros/Cons:
+ Moderate complexity
+ Suits for any client/PG backend
+ Good isolation from other Ceph components
- Limited applicability
- additional 50-200% CPU load for the cluster since we compress each
replica/EC shard independently
- no inter-component traffic saving
- recovery procedure requires decompress/recompress sequence
Mirantis ( me specifically ) will start blueprint/POC creation for this
promptly. I'm planning to attend daily RBD syncup regularly to inform on
the progress.
3) Add full compression support at BlueStore. This includes 2) + support
for random object writes.
Pros/Cons:
+ Severe complexity
+ Suits for any client/PG backend
+ Good isolation from other Ceph components
- additional 50-200% CPU load for the cluster since we compress each
replica/EC shard independently
- no inter-component traffic saving
- recovery procedure requires decompress/recompress sequence
On-Hold for now. Will require insert/delete data range for the store.
4) Add basic ( append only ) compression support at OSD using interim
PGBackend.
Pros/Cons:
+ Moderate complexity
+ Suits for any client/PG backend
+ Data compressed before replication/"EC inflation"
+ inter-component traffic saving
+ recovery procedure don't need decompress/recompress sequence
- Too tight(danger) integration into Ceph internals
- Limited applicability
- Bad experience with "append only" notion for EC and desire to avoid
that for compression
Rejected ( Personally I'd prefer this option with subsequent mutation to
full RW support. The rationale is the reduced CPU load comparing to
options 2 & 3)
Any additional comments/suggestions are welcome.
Thanks,
Igor
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