Automatic GAP Resolution

I will explan Automatic GAP Resolution in Oracle Data Guard in this article. You may want to read below articles two understand Oracle Data Guard architecture.

Oracle Data Guard Architecture“,
Oracle Data Guard Redo Transport Services

What is Redo GAP?

In some cases, the LNS background process cannot transmit the generated redo data quickly enough and REDO GAP occurs. Some reasons for the occurrence of redo gap are as follows;

  • Too many commits
  • Network interruption
  • Closing the standby database

What is Automatic GAP Resolution?

  • When the Redo GAP occurs, the LGWR background process continues to write to the “Online Redo Log” file, and when Redo is full, it continues to “Switch” to the next redo log file.
  • When the switch occurs, the ARCH background process generates an archive. The ARCH background process continues to generate an archive file until the Primary to Standby problem is resolved.
  • The ARCH process running on the primary database regularly pings the standby database during the interruption and checks to see if it responds.

When the problem between Primary and Standby is solved;

  • The ARCH process in the primary database determines the last received log file from the Primary by querying the “Standby Control File” over the RFS operation in the standby database.
  • Data Guard automatically detects the “Archive Log Files” required to close the gap and tries to close the gap via the ARCH process.

Check Log GAP Between Primary and Standby

You can learn log gap with two scripts;

Check Last Processed Archive at Stanby(Execute the script in Primary):

Check How Much LAG is between Primary and Standby(Execute the script in Standby):

Onur ARDAHANLI
Author: Onur ARDAHANLI

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