环境：Oracle 11.2.0.4 DG
故障现象：
客户在备库告警日志中发现GAP sequence提示信息： 

Mon Nov 21 09:53:29 2016 Media Recovery Waiting for thread 1 sequence 12034 Fetching gap sequence in thread 1, gap sequence 12034-12078 Mon Nov 21 09:55:20 2016 FAL[client]: Failed to request gap sequence
 GAP - thread 1 sequence 12034-12078 DBID 3493955325 branch 881855745 FAL[client]: All defined FAL servers have been attempted.
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Check that the CONTROL_FILE_RECORD_KEEP_TIME initialization
parameter is defined to a value that's sufficiently large enough to maintain adequate log switch information to resolve
archivelog gaps.
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修复过程：