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https://issues.apache.org/jira/browse/HIVE-27473?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17777689#comment-17777689
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okumin commented on HIVE-27473:
-------------------------------
This might not be as trivial as I originally expected.
SessionHiveMetaStoreClient and HiveMetaStoreClientWithLocalCache are coupled
with not IMetaStoreClient but HiveMetaStoreClient.
Let's see the case of `getTable`. The public endpoint is defined as
[IMetaStoreClient#getTable|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/IMetaStoreClient.java#L735].
However, SessionHiveMetaStoreClient, HiveMetaStoreClientWithLocalCache, and
HiveMetaStoreClient are coupled with not only the public API,`getTable`, but
also another non-public API, `getTableInternal`.
1. A client calls
[SessionHiveMetaStoreClient#getTable|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/SessionHiveMetaStoreClient.java#L277]
2. The method checks if a tmp table exists. If it doesn't exist, the method
calls
[super.getTable|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/SessionHiveMetaStoreClient.java#L284]
3.
[HiveMetaStoreClient#getTable|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/HiveMetaStoreClient.java#L2780]
is invoked
4. The method calls
[getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/HiveMetaStoreClient.java#L2790]
5.
[SessionHiveMetaStoreClient#getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/SessionHiveMetaStoreClient.java#L2094]
is invoked
6. The method checks query level cache. If not cached,
[super.getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/SessionHiveMetaStoreClient.java#L2108]
is called
7.
[HiveMetaStoreClientWithLocalCache#getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/HiveMetaStoreClientWithLocalCache.java#L273]
is invoked
8. The method checks if metastore client cache. If not cached,
[super.getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/ql/src/java/org/apache/hadoop/hive/ql/metadata/HiveMetaStoreClientWithLocalCache.java#L282]
is called
9.
[HiveMetaStoreClient#getTableInternal|https://github.com/apache/hive/blob/b02cef4fe943b9aba597dcdfd3b8f3d3a5efca3e/standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/HiveMetaStoreClient.java#L2731]
is invoked and the actual access to HMS happens
Those have mutual dependencies, meaning SessionHiveMetaStoreClient invokes
steps implemented in HiveMetaStoreClient. HiveMetaStoreClient also invokes
steps implemented in SessionHiveMetaStoreClient. I guess we need to restructure
the dependency in order to make them composable.
> Make SessionHiveMetaStoreClient and HiveMetaStoreClientWithLocalCache
> composable
> --------------------------------------------------------------------------------
>
> Key: HIVE-27473
> URL: https://issues.apache.org/jira/browse/HIVE-27473
> Project: Hive
> Issue Type: Improvement
> Components: Hive
> Affects Versions: 4.0.0-alpha-2
> Reporter: okumin
> Assignee: okumin
> Priority: Major
>
> Currently, we implement the two classes using inheritance. It assumes we
> always use a single implementation of IMetaStoreClient.
> Some community members have been willing to make IMetaStoreClient pluggable
> as proposed in HIVE-12679. Considering the use case, we should provide the
> additional traits with composition over inheritance.
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