Question

我想知道如何正确确定c3p0 max_statements使用的值。我已经经历了一些缓存死锁，这似乎指向我基于所有SO Q＆amp; A I读过的max_statements配置。

我正在使用mysql，当我进行一些多线程我有4个活动线程时，就会发生死锁。

我的配置

<property name="hibernate.connection.provider_class">org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider</property>
<property name="hibernate.c3p0.min_size">10</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.max_size">50</property>
<property name="hibernate.c3p0.idle_test_period">1800</property>
<property name="hibernate.c3p0.timeout">3600</property>

例外

[WARN] async.ThreadPoolAsynchronousRunner com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@72df1587 -- APPARENT DEADLOCK!!! Complete Status:
    Managed Threads: 3
    Active Threads: 3
    Active Tasks:
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@e877a61
            on thread: C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#2
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@109b1150
            on thread: C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#0
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@3eb42946
            on thread: C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#1
    Pending Tasks:
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$1StmtAcquireTask@52729f95
Pool thread stack traces:
    Thread[C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#0,5,main]
        com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2765)
        com.mysql.jdbc.StatementImpl.close(StatementImpl.java:541)
        com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:938)
        com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)
    Thread[C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#1,5,main]
        com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2765)
        com.mysql.jdbc.StatementImpl.close(StatementImpl.java:541)
        com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:938)
        com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)
    Thread[C3P0PooledConnectionPoolManager[identityToken->1hge0wd9a1o1iea71i8u346|1a799bb]-HelperThread-#2,5,main]
        com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2765)
        com.mysql.jdbc.StatementImpl.close(StatementImpl.java:541)
        com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
        com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:938)
        com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)

所以我的问题是如何确定这些值应该是什么。我确定必须在没有猜测的情况下做到这一点。

我读过的文章

should i activate c3p0 statement pooling?

How to trace and prevent the deadlock appeared in c3po which is running in seperate processes?

Answer 1

要解决与Oracle / jTDS / mySQL下的Statement缓存相关的死锁，请确保您使用的是最近的c3p0（0.9.5.1是当前版本），请参阅statementCacheNumDeferredCloseThreads和Configuring Statement Pooling

TL; DR set config param

<property name="hibernate.c3p0.statementCacheNumDeferredCloseThreads">1</property>

max_statements的确切值只是偶然与此问题相关联。如果max_statements太小，您将不必要地翻译语句，并且在一些驱动程序中与PreparedStatement.close()的脆弱性相关的此问题将更频繁地出现。

但是，对于hibernate.c3p0.max_statements 50的池，maxPoolSize的值太小。即使在修复死锁问题之后，通过语句转换也会减少或消除语句缓存的任何性能优势。要计算hibernate.c3p0.max_statements（映射到c3p0.maxStatements）的良好值，请计算应用程序中经常使用的不同PreparedStatements的数量，并将其乘以{{1} （或者在你的情况下maxPoolSize）。或者，只需将hibernate.c3p0.max_size设置为应用程序频繁使用的不同PreparedStatements的数量。

请参阅maxStatements，maxStatementsPerConnection和Configuring Statement Pooling。

如何确定c3p0 max_statements

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