Multi-object transaction support¶

Summary
This is for multi-object transaction support.

Owners

Li Wang (Ubuntukylin)
Yunchuan Wen (Ubuntukylin)
Name

Interested Parties
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Current Status
Please describe the current status of Ceph as it relates to this blueprint. Is there something that this replaces? Are there current features that are related?

Detailed Description
(1) Allow client to define the following struct,
struct MultiObjectTransaction {
map<hobject_t, ObjectWriteOperation> object_ops;
hobject_t master;
};
based on this, client could send a group of ops through MOSDOp to the PG coressponding to master object, call it master PG

(2) Master PG receive the MOSDOp from client, extract the ObjectWriteOperations on objects belonging to different PGs, and them to corresponding PGs, call them slave PGs

(3) Slave PG receive MOSDOp from master, if there are pending conventional single-object transactions share
the operation on the same object, wait until them finished; If there are pending multi-object transactions share the operation on the same object, return EAGAIN (we can not wait here, otherwise may dead lock); Otherwise, contruct the transaction in the conventional way, return master PG PREPARE_ACK, if error occured,
for example, a read then comparation failed, then return error number

Work items
This section should contain a list of work tasks created by this blueprint. Please include engineering tasks as well as related build/release and documentation work. If this blueprint requires cleanup of deprecated features, please list those tasks as well.

Coding tasks
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Build / release tasks
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Documentation tasks
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Deprecation tasks
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