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Title
What is meant by "using archive log ....." messages in event_log? -
Description
At times event log shows the following messages:
01/17/08 10:13 Notice: Using archive log
/u01/app/oracle/product/9.2.0/dbs/arch/ABC_28802.arc [sp_ocap/1963]
01/17/08 10:13 Notice: Using archive log
/u01/app/oracle/product/9.2.0/dbs/arch/ABC_28803.arc [sp_ocap/1963]What do these messages signify? Does Shareplex not always use the archive logs? If it does, why are they only visible now and not always?
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Cause
Informational solution.
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Resolution
These messages are telling that Shareplex is currently reading from the archive logs. Normally Shareplex's Capture process reads from the online redologs to gather changes to the source database and it only reads from the archive logs in the following circumstances:
1. There is a large batch job executed on the source database and the log switches occurred too fast for the Capture process to catch up whereby the changes have been archived in the archive logs even while Capture is gathering them. Capture first attempts to read from the online redo logs and if it does not find them in the event that they are archived, it will look further in the archive destination to see if it can find those redo logs in archive mode.
2. If Shareplex or Capture process is shutdown for a long time and then restarted, the Capture process attempts to process the database changes from the point where it was at, prior to shutdown. It is able to locate the correct log to process on the basis of the SCN # it processed last. If the logs have been archived at this time, it will read them the archive destination (typically pointed to by the parameter LOG_ARCHIVE_DEST).
3. If the Capture process was errored out for a long time and then restarted after the error condition was addressed, it may end up reading the archive logs to gather changes.
4. Capture may be slowed down due to a number of reasons including running in debug mode, I/O problems, etc, and may end up reading from the archive logs till the underlying causes for its slowness are addressed.