Java數據庫連接池C3P0-0.9.2-pre3 發布

C3P0是一個開放源代碼的JDBC連接池，Hibernate的發行包中默認使用此連接池。傳說性能最好。

C3P0在沉寂了多年之后，終于迎來了更新，目前常用的穩定版是：0.9.1.2，現在最新版本： 0.9.2-pre2（開發版 0.9.2-pre3），C3P0的最新代碼已經遷移到GitHub上了：https://github.com/swaldman/c3p0

0.9.2-pre2下載地址：http://sourceforge.net/projects/c3p0/files/c3p0-bin/

0.9.3-pre3下載地址：https://oss.sonatype.org/content/repositories/snapshots/com/mchange/c3p0/0.9.2-pre3-SNAPSHOT/

 Changelog:

c3p0-0.9.2-pre3
Some highlights:

+ Some JDBC drivers freeze up if cached Statements are close()ed while their parent
  Connections are in use. Previously users of these drivers (Oracle, JTDS) generally 
  had to forego Statement caching to avoid deadlocks. C3P0's statement cache can now 
  be set to cautiously close Statements only when the parent Connections are known
  to be idle. If you experience "APPARENT DEADLOCKS" due to StatementCloseTasks, set

      c3p0.statementCacheNumDeferredCloseThreads=1

  and they should go away!

+ There are some other minor improvements and fixes: 

    -- the more granular and efficient "scattered" Connection acquisition algorithm that 
       was "experimental" in the previous release is enabled by default

    -- unreturned Connections that are timed out (bad! bad!) are either rolled back (default)
       or committed before close(), respecting your unresolved transaction configuration.
       (see config parameter unresolvedConnectionTimeout in docs).

+ You must now include two jar files (c3p0 and mchange-commons-java) in your CLASSPATH
  rather than just one. Both can be found in the lib directory of the binary distribution.
  (Please provide feedback; if this is very inconvenient I can bundle it all up into 
  a unified jar.)

Some structural changes:

+ Development of c3p0 and mchange-commons-java have migrated to github:

     https://github.com/swaldman/c3p0
     https://github.com/swaldman/mchange-commons-java

   Note that c3p0 depends (heavily) on the mchange-commons library.


c3p0-0.9.2-pre2
    -- Added support for deployment to Maven central repository to build.xml,
       and noted this version's coordinates in the repository.
    -- Added a src directory to the distribution, containing jarred java
       sources (including codegenerated sources) intended for debuggers/IDEs.
       As a convenience, mchange-commons-java sources are included as well.
    -- Fixed issue where idle Connections being tested by the pool
       were not properly marked with the statement cache as "in-use".
    -- Updated the build file to make it easy to update versions and dates
       on source code headers.
    -- ResultSets are now automatically closed and their proxies dereferenced
       as soon as parent Statements are closed, rather than waiting for the parent 
       Connection to close as we did before. Thanks to jo-hennig and soronthar for 
       calling attention to this issue.
    -- Modified (in mchange commons library) ThreadPoolAsynchronousRunner to
       occasionally (stochastically) call Timer.purge() when maxAdministrativeTaskTime
       settings leads to frequent cancellations of TimerTasks. Thanks to Kevin Conaway, 
       who observed memory issues from the piling up of canceled but unpurged TimerTasks.
    -- Modified (in mchange commons library) VersionUtils to be more tolerant
       of unusual version Strings. Thanks to martyhu for the suggestion.   
    -- When a ProxyConnection is marked closed, we now fire a connectionClosed
       event even if an Exception occurred during cleanup, to be sure that proxies 
       detach. We still fire a connectionErrorOccurred prior to connectionClosed, 
       so that listeners (especially C3P0PooledConnectionPool) can invalidate the 
       can't-be-cleaned-up PooledConnection.
    -- Modified GooGooStatementCache to call clearBatch on PreparedStatement checkin, 
       so that stale batches from prior use of Statements are never visible to new 
       users. Many thanks to David Carr for pointing out the problem and the fix.
    -- getWarnings and clearWarnings no longer set the txn_known_resolved flag to false.
       Thanks to Manuel Darveau for pointing out the unnecessary caution.
    -- Gave C3P0PooledConnectionPoolManager's timer a name. Thanks to Matt Kusnierz 
       for the suggestion.
    -- Fixed an infinite loop in ComboPooledDataSource, which occurred following
       some Exceptions, which provoked calls to toString() to build the Exception
       message, which call itself provoked an Exception, ad infinitum. All potentially
       Exception-provoking attribute lookups are now excluded from toString(). Many
       thanks to Svante v. Erichsen for calling attention to this problem and 
       suggesting a fix.
    -- Modified the build so that JDK 1.4 compatible versions of c3p0-0.9.2
       can be generated easily. (c3p0-0.9.2 will be the last version of c3p0
       to support JDK 1.4 builds.)
        -- Moved development onto github. See https://github.com/swaldman/c3p0, with
       a dependency against https://github.com/swaldman/mchange-commons-java


c3p0-0.9.2-pre1
        -- Rationalized management of the ConnectionEventListener that checks in 
           PooledConnections on proxy Connection close(). Now added on check-out and 
           removed on check-in, rather than being always present but temporarily removed 
           during administrative tasks.
    -- Implemented asynchronous Statement destroyer, hopefully completing the task of
           making the statement cache robust to drivers that cannot deal with Statements
           being closed underneath Connections still in use (e.g. Oracle, JTDS). Note
           that this implementation requires at least one dedicated Thread for statement
           destruction (if we used the common Thread pool, there will be deadlocks as
           Statement close tasks await not-in-use Connections, while Connection-related
           tasks can't be completed because the Thread pool is saturated with Statement
           close tasks. Stats about the asynchronous Statement destroyer are available
           via the JMX MBean, prefixed statementDestroyer. Setting the new config parameter 
           c3p0.statementCacheNumDeferredCloseThreads enables the fix. 
    -- Resolved a potential race condition that could lead to pool freezes, especially
       when acquisitions occasionally fail and acquireIncrement is set to 1. [Many
           thanks to Brendan Dougherty for carefully describing this issue.]
    -- Added a guard to BasicResourcePool.doAcquire() to ensure that the pool has
           not been closed or broken before assimilating a task [Many thanks to
           Sean Rohead for tracking down this issue and suggesting the fix.]
    -- Made SCATTERED_ACQUIRE_TASK default to true. This provides much better overall
       performance for Connection acquisition from potentially unreliable sources
    -- Modifed to ensure that unresolved transaction settings apply to expired
       unreturned Connections. (see config params autoCommitOnClose and
           forceIgnoreUnresolvedTransactions) [Thanks to Matthew Lieder for calling 
       attention to this issue.]
    -- Cleaned up Statement cache fix that ensures no statements are closed while
           their parent Connection is in use. By default, the fix is not enabled, because
       it's extra work that most databases don't need. [Most drivers support Statement
       close() while a parent Connection is in use, so the extra work is unnecessary.] 
    -- Separated traditional build into two libraries, mchange-commons and c3p0.   
    -- Modified GooGooStatementCache and C3P0PooledConnectionPool to ensure that
       1) the Statement cache knows which Connections are currently in use by outside
       clients; and 2) the Statement cache refuses to cull Statements belonging to 
       Connections in use. Theoretically, drivers should support asynchronous statement
       close. In practice, some drivers don't do so nicely, or block pending completion
       of other (potentially long) operations, leading to APPARENT DEADLOCKS. (Oracle
       users in particular have reported deadlocks in which all pool threads are blocked
       on Statement close tasks.) [Many, many thanks to Ovidiu Feodorov for a very detailed
       account of problems that occur under c3p0 when very long queries are executed under 
       Oracle!]
    -- Defined a NullMLogger, and modified Log4jMLog to use that, instead of a broken
       log4j MLogger, if c3p0's logging library fails to acquire a non-null Log4j logger.
       Thanks to Oli Glimmer for calling attention to this issue. (Strange NPEs due to
       apparently null log4j loggers have been encountered before, and previous attempts
       to resolve apparently weren't adequate.)
    -- Fixed a problem whereby ThreadPoolAsynchronousRunner was not robust to Errors provoked
       during task execution. [Thanks to George Khoshy for reporting this issue.]
    -- Made VersionUtils more robust to cases where some components of the java.version system
       property are non-integral [Thanks to Dirk Weigenand for calling attention to this problem,
       and suggesting a solution!]

 雖然C3P0-0.9.2 還不是穩定版，但是很值得期待，希望性能更好，更穩定。