[GitHub] merlimat opened a new pull request #1264: Refactored LAC cache in DbLedgerStorage

[GitBox <gi...@apache.org>]

merlimat opened a new pull request #1264: Refactored LAC cache in DbLedgerStorage
URL: https://github.com/apache/bookkeeper/pull/1264
 
 
   The `TransientLedgerInfo` cache that holds the LAC (or explicit lac) for all ledgers has showed up in the profiler as a big contention point. 
   
   ### Modifications 
   
    * Only add an item in `TransientLedgerInfo` is someone has asked for LAC or has set explicity LAC. This will save lot of memory if many ledger are not requiring the LAC info.
    * Use `ConcurrentLongHashMap` to store the `TransientLedgerInfo`. There are few advantages: 
      - Key in the map is `long` and doesn't need boxing
      - The `get()` operation uses a stamped lock which is ideal in cases the number of `get()` is way bigger than `put()` operations, since it only needs a volatile variable read. In this case the map is only updated when new ledgers are added / removed, but we do a `get()` on each `addEntry()` operation.
     - Schedule periodical cleanup of the map for stale ledger info entries

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