RMAN backup – Performance

1. If the V$BACKUP_ASYNC_IO view is empty and the V$BACKUP_SYNC_IO view is not empty, then the backup is not being performed in asynchronous mode. So enable backup tape I/O slaves, and if the system does not support native asynchronous I/O, then also enable backup disk I/O slaves.
2. Query V$BACKUP_ASYNC_IO to determine the effective reading speed during the backup. This value is reported in the column
EFFECTIVE_BYTES_PER_SECOND in the row that has the TYPE column equal to AGREGGATE. This row represents the backup speed. Sometimes backups are slow not because reading or writing is slow, but because of other issues: connecting to the media manager, retrying while starting media manager processes, committing the backup of the tape, and so on. In such cases, troubleshoot the problem in the media management software.
3. Investigate the IO_COUNT, READY, SHORT_WAITS, and LONG_WAITS
columns:
· The column IO_COUNTS represents the total number of the I/O calls.
· The READY column is the number of asynchronous I/O reads or writes for which a buffer was immediately ready for use.
· The column SHORT_WAITS represents the number of times that a buffer was not immediately available, but a buffer became available after doing a nonblocking poll for I/O completion.
· LONG_WAITS is the number of times that a buffer was not immediately available, and only became available after a blocking wait was issued. In other words, the number of I/O calls where Oracle waited for the disk or tape.

select SID, SERIAL, USE_COUNT,
RMAN_STATUS_RECID, RMAN_STATUS_STAMP,DEVICE_TYPE, TYPE,
STATUS,FILENAME, SET_COUNT, SET_STAMP, BUFFER_SIZE, BUFFER_COUNT,
TOTAL_BYTES, OPEN_TIME, CLOSE_TIME, ELAPSED_TIME, MAXOPENFILES, BYTES,
EFFECTIVE_BYTES_PER_SECOND, IO_COUNT, READY, SHORT_WAITS, SHORT_WAIT_TIME_TOTAL,
SHORT_WAIT_TIME_MAX, LONG_WAITS, LONG_WAIT_TIME_TOTAL, LONG_WAIT_TIME_MAX
from gv$backup_async_io where inst_id = userenv(‘Instance’)

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One Response

  1. still not really understand the SHORT_WAITS meaning

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