[HIVE-9741] Refactor MetaStoreDirectSql constructor by removing DB queries out of critical section

• Type: Bug
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.0.0
• Component/s: Metastore
• Assignee: Xiaobing Zhou
• Reporter: Xiaobing Zhou
• Created: 20/Feb/15 18:05
• Updated: 26/Feb/15 23:48

Description

MetaStoreDirectSql constructor is querying DB to determine dbType, which leads to too many DB queries to make megastore slow as ObjectStore.setConf might be called frequently. Moreover, ObjectStore.setConf begins/ends with lock acquire/release, if the underlying DB hangs somehow, lock is never released and all hereafter incoming requests are blocked.

Two points:
1. Using getProductName based JDBC driver to get dbType info.
2. Since metastore auto-creaton is disabled by default, it'd better bypass ensureDbInit() and runTestQuery() in order to avoid DB queries within critical section of setConf.

Here’s stack trace:
MetaStoreDirectSql.determineDbType(...)
MetaStoreDirectSql.MetaStoreDirectSql(...)
ObjectStore.initialize(...)
ObjectStore.setConf(…)

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