消息处理API，由客户端通过网络连接GTM Master调用，这些消息处理API通过上述函数达到目的。
ProcessGetGIDDataTransactionCommand() --> MSG_TXN_GET_GID_DATA
ProcessGXIDListCommand() --> MSG_TXN_GXID_LIST
ProcessGetGXIDTransactionCommand() --> MSG_TXN_GET_GXID
ProcessGetNextGXIDTransactionCommand() --> MSG_TXN_GET_NEXT_GXID
ProcessReportXminCommand()
ProcessBeginTransactionCommand() --> MSG_TXN_BEGIN message
ProcessBeginTransactionGetGXIDCommand() --> MSG_TXN_BEGIN_GETGXID
ProcessBeginTransactionGetGXIDAutovacuumCommand() --> MSG_TXN_BEGIN_GETGXID_AUTOVACUUM
ProcessBeginTransactionGetGXIDCommandMulti() --> MSG_TXN_BEGIN_GETGXID_MULTI
ProcessBkupBeginTransactionCommand() --> MSG_BKUP_TXN_BEGIN
ProcessBkupBeginTransactionGetGXIDCommand() --> MSG_BKUP_TXN_BEGIN_GETGXID
ProcessBkupBeginTransactionGetGXIDCommandMulti() --> MSG_BKUP_BEGIN_TXN_GETGXID_MULTI
ProcessBkupBeginTransactionGetGXIDAutovacuumCommand() --> MSG_BKUP_TXN_BEGIN_GETGXID_AUTOVACUUM
ProcessRollbackTransactionCommand() --> MSG_TXN_ROLLBACK/MSG_BKUP_TXN_ROLLBACK
ProcessRollbackTransactionCommandMulti() --> MSG_TXN_ROLLBACK_MULTI/MSG_BKUP_TXN_ROLLBACK_MULTIMSG_TXN_COMMIT_MULTI/MSG_BKUP_TXN_COMMIT_MULTI
ProcessCommitTransactionCommand() --> MSG_TXN_COMMIT/MSG_BKUP_TXN_COMMIT
ProcessCommitTransactionCommandMulti()
ProcessCommitPreparedTransactionCommand() --> MSG_TXN_COMMIT_PREPARED/MSG_BKUP_TXN_COMMIT_PREPARED
ProcessPrepareTransactionCommand() --> MSG_TXN_PREPARE/MSG_BKUP_TXN_PREPARE
ProcessStartPreparedTransactionCommand() --> MSG_TXN_START_PREPARED/MSG_BKUP_TXN_START_PREPARED
BeginTransaction
ProcessBeginTransactionCommand() --> MSG_TXN_BEGIN message
ProcessBeginTransactionGetGXIDCommand() --> MSG_TXN_BEGIN_GETGXID
ProcessBeginTransactionGetGXIDAutovacuumCommand() --> MSG_TXN_BEGIN_GETGXID_AUTOVACUUM
ProcessBeginTransactionGetGXIDCommandMulti() -->
ProcessBeginTransactionCommand函数的流程如下：从message中取出事务隔离级别、read only、session字符串，调用GTM_BeginTransaction函数启动新事务，获取时间戳，调用bkup_begin_transaction向standby同步事务，填充返回消息并将消息返回。
ProcessBeginTransactionGetGXIDCommand函数的流程如下：从message中取出事务隔离级别、read only、session字符串，获取时间戳，调用GTM_BeginTransaction函数启动新事务，调用GTM_GetGlobalTransactionId函数获取全局事务ID，调用bkup_begin_transaction_gxid向standby同步事务，填充返回消息并将消息返回。
ProcessBeginTransactionGetGXIDAutovacuumCommand函数取出事务隔离级别、txn client id，调用GTM_BeginTransaction函数启动新事务，调用GTM_GetGlobalTransactionId函数获取全局事务ID，调用GTM_SetDoVacuum函数，调用bkup_begin_transaction_autovacuum向standby同步事务，填充返回消息并将消息返回。
ProcessBeginTransactionGetGXIDCommandMulti函数先获取请求事务数、再循环获取事务隔离级别、read only、session字符串，txn client id，调用GTM_BeginTransactionMulti，获取时间戳，调用bkup_begin_transaction_multi向standby同步事务，填充返回消息并将消息返回。
ProcessBkupBeginTransactionCommand() --> MSG_BKUP_TXN_BEGIN
ProcessBkupBeginTransactionGetGXIDCommand() --> MSG_BKUP_TXN_BEGIN_GETGXID
ProcessBkupBeginTransactionGetGXIDCommandMulti() --> MSG_BKUP_BEGIN_TXN_GETGXID_MULTI
ProcessBkupBeginTransactionGetGXIDAutovacuumCommand() -->
ProcessBkupBeginTransactionCommand函数从message中取出事务隔离级别、read only、session字符串、client id，调用GTM_BkupBeginTransaction函数。
ProcessBkupBeginTransactionGetGXIDCommand函数取出事务隔离级别、read only、session字符串、txn client id，调用GTM_BkupBeginTransactionGetGXID函数。
ProcessBkupBeginTransactionGetGXIDCommandMulti先获取请求事务数、再循环获取事务隔离级别、read only、session字符串，txn client id，调用GTM_BkupBeginTransactionGetGXIDMulti函数。
ProcessBkupBeginTransactionGetGXIDAutovacuumCommand函数取出事务隔离级别、txn client id，调用GTM_BkupBeginTransactionGetGXID函数，调用GTM_SetDoVacuum函数。
CommitTransaction
ProcessCommitTransactionCommand() --> MSG_TXN_COMMIT/MSG_BKUP_TXN_COMMIT
ProcessCommitTransactionCommandMulti()
ProcessCommitPreparedTransactionCommand() --> MSG_TXN_COMMIT_PREPARED/MSG_BKUP_TXN_COMMIT_PREPARED
ProcessCommitTransactionCommand函数从消息中获取gxid，通过GTM_GXIDToHandle(gxid)获取事务句柄，然后从消息中获取等待xid的数量，获取其等待的所有xid，调用GTM_CommitTransaction函数，调用bkup_commit_transaction向standby同步事务，填充返回消息并将消息返回。
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ProcessCommitPreparedTransactionCommand函数
