Fangshi Li created HIVE-19261:
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Summary: Avro SerDe's InstanceCache should not be synchronized on
retrieve
Key: HIVE-19261
URL: https://issues.apache.org/jira/browse/HIVE-19261
Project: Hive
Issue Type: Improvement
Reporter: Fangshi Li
Assignee: Fangshi Li
In HIVE-16175, upstream made a patch to fix the thread safety issue in
AvroSerDe's InstanceCache. This fix made the retrieve method in InstanceCache
synchronized. While it should make InstanceCache thread-safe, adding
synchronized on retrieve for the cache can be expensive in highly concurrent
environment like Spark, as multiple threads need to be synchronized on entering
the retrieve method.
We are proposing another way to fix this thread safety issue by making the
underlying map of InstanceCache as ConcurrentHashMap. Ideally, we can use
atomic computeIfAbsent in the retrieve method to avoid synchronizing the entire
method.
While computeIfAbsent is only available on java 8 and java 7 is still supported
in Hive,
/we use a pattern to simulate the behavior of computeIfAbsent. In the future,
we should move to computeIfAbsent when Hive requires java 8.
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