[BOOKKEEPER-961] Assing read/write request for same ledger to a single thread

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.4.0
• Fix Version/s: 4.5.0
• Assignee: Matteo Merli
• Reporter: Matteo Merli
• Created: 02/Nov/16 20:31
• Updated: 15/Nov/16 17:23
• Resolved: 12/Nov/16 02:36

Description

When entries for the same ledger are processed by the bookie we should avoid
the reordering of the request. Currently, if multiple read/write threads are
configured, the requests will be passed to the executor and writes for same
ledger will be spread across multiple threads.

This poses 2 issues:

1. Mutex contention to access the LedgerDescriptor
2. If the client receives add-entry acks out of order it has anyway to wait
   for the acks of previous entries before acknowledging the whole sequence
   to the application. In practice, the reordering is increasing the latency
   experienced by the application.

Issue Links

• links to: GitHub Pull Request #69