ZanderXu created HDFS-17473:
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Summary: [FGL] Make quota related operations thread-safe
Key: HDFS-17473
URL: https://issues.apache.org/jira/browse/HDFS-17473
Project: Hadoop HDFS
Issue Type: Sub-task
Reporter: ZanderXu
Assignee: ZanderXu
Concurrent operations on directory tree may cause Quota updates and
verification to not be thread-safe.
For example:
# Supposing there is directory _/a/b_ and quota is on inode _a_ and _b_
# There are some directories and files under {_}/a/b{_}, such as:
{_}/a/b/c/d1{_}, _/a/b/d/f1.txt_
# Supposing there is a create operation under _/a/b/c/d1_ and there is a
addBlock operation on _/a/b/d/f1.txt_
# These two operations can be handled concurrently by namenode
# They will update the quota on inode a concurrently since these operations
just hold the read lock of the inode _a_ and {_}b{_}.
# so we should make quota-related thread safe.
There are two solutions to make quota-related thread safe。
Solution one: Hold the write lock of the first iNode with Quota set when
resolvePath
* Directly hold the write lock of iNode _a_ so that all operations involving
subtree _/a_ can be handled safety.
* Due to lower concurrency, maximum improvements cannot be achieved.
* But the implementation is simple and straightforward.
Solution two: Lock all QuotaFeatures during quota verification or update
* Still hold the read lock of iNode a and b
* Lock all QuotaFeatures involved in this operations, when validating or
updating quotas.
* Maximum improvements can be achieved.
* But the implementation is a little complex
** Add a lock for each QuotaFeature
** Acquire locks for all involving QuotaFeature
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