tianhang tang created HBASE-26850:
-------------------------------------
Summary: Optimize the implementation of LRUCache in LRUDictionary
Key: HBASE-26850
URL: https://issues.apache.org/jira/browse/HBASE-26850
Project: HBase
Issue Type: Improvement
Components: wal
Affects Versions: 2.4.11, 3.0.0-alpha-2, 1.7.1
Reporter: tianhang tang
Assignee: tianhang tang
Attachments: image-2022-03-16-17-13-00-871.png
During my research on HBASE-26849, I found that there seems to be something
wrong with the implementation of LRUDictionary.
It uses array to save data, and uses hashMap to save array index. If there are
multiple identical elements, multiple copies will be stored in the array, but
there is only one mapping from one element to the array index in the map.
In this way, when the first element is eliminated, there is no way for the
other elements to find the index.
Then i try to dig out the write link.
The stack of write is:
{code:java}
RingBufferEventHandler#onEvent
->
RingBufferEventHandler#append
->
ProtobufLogWriter#append
->
CompressedKvEncoder#write
->
LRUDictionary#findEntry{code}
BidirectionalLRUMap#findIdx will be executed first in LRUDictionary#findEntry:
!image-2022-03-16-17-13-00-871.png!
If the LRUCache already exists, it will moveToHead directly and return the
existing node, and will not write multiple times in the array.
After debug verification, it is indeed the case.
However, the current LRUCache directly exposes _addEntry_ to the outside, which
I think we can do it a little more elegantly.
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