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https://issues.apache.org/jira/browse/HIVE-19261?focusedWorklogId=326191&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-326191
]
ASF GitHub Bot logged work on HIVE-19261:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 10/Oct/19 08:59
Start Date: 10/Oct/19 08:59
Worklog Time Spent: 10m
Work Description: dlavati commented on pull request #807: HIVE-19261:
Avro SerDe's InstanceCache should not be synchronized on retrieve
URL: https://github.com/apache/hive/pull/807#discussion_r333403943
##########
File path: serde/src/java/org/apache/hadoop/hive/serde2/avro/InstanceCache.java
##########
@@ -51,20 +51,19 @@ public Instance retrieve(SeedObject hv) throws
AvroSerdeException {
* Retrieve (or create if it doesn't exist) the correct Instance for this
* SeedObject using 'seenSchemas' to resolve circular references
*/
- public synchronized Instance retrieve(SeedObject hv,
- Set<SeedObject> seenSchemas) throws AvroSerdeException {
+ public Instance retrieve(SeedObject hv, Set<SeedObject> seenSchemas)
+ throws AvroSerdeException {
if(LOG.isDebugEnabled()) LOG.debug("Checking for hv: " + hv.toString());
if(cache.containsKey(hv)) {
if(LOG.isDebugEnabled()) LOG.debug("Returning cache result.");
return cache.get(hv);
+ } else {
+ if(LOG.isDebugEnabled()) LOG.debug("Creating new instance and storing in
cache");
Review comment:
@xhumanoid thanks for the contribution! I don't have committer rights to
approve your patch, but LGTM with a few comments:
- a small nitpick, but AFAIK, `isDebugEnabled` doesn't provide benefits
here, only if you'd append/toString an expensive operation's result (yes, this
is also ignored in a lot of places 😄)
- to approve (+1) your changes, you'll have to become the assignee of the
jira ticket that's currently under Fangshi Li (if that's fine with him) and
change it's state with `Submit a patch` with an attached patch file (the
previously attached file didn't get checked, as the issue state didn't change)
- once all tests pass for it (might require a few reattachments/reruns),
then someone will be able to approve it (also see
https://cwiki.apache.org/confluence/display/Hive/HowToContribute#HowToContribute-CreatingaPatch)
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Issue Time Tracking
-------------------
Worklog Id: (was: 326191)
Time Spent: 40m (was: 0.5h)
> 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
> Priority: Major
> Labels: pull-request-available
> Attachments: HIVE-19261.1.patch
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> 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, making retrieve
> synchronized for the cache can be expensive in highly concurrent environment
> like Spark, as multiple threads need to be synchronized on entering the
> entire 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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