Databases Reference
In-Depth Information
Solution
The Exadata Storage Server (ESS) software can skip blocks at the Cell level directly while taking an incremental
backup. To find out how many blocks were skipped, issue the following query while connected as a user with access to
the dynamic performance views, typically SYS:
col blocks_skipped_in_cell head 'Cell Skip'
col cell_rman_eff head 'RMAN Eff%' format 999.99
select file#, blocks, blocks_read, datafile_blocks, blocks_skipped_in_cell, 100*
blocks_skipped_in_cell/blocks_read cell_rman_eff
from v$backup_datafile
/
Here is the output:
FILE# BLOCKS BLOCKS_READ DATAFILE_BLOCKS Cell Skip RMAN Eff%
---------- ---------- ----------- --------------- ---------- ---------
547 2033 92801 102400 0 .00
618 1529 77441 89600 0 .00
622 1397 72321 76800 0 .00
303 1697 77441 89600 0 .00
595 1865 87681 89600 0 .00
616 1265 62081 76800 0 .00
301 1697 77441 89600 0 .00
369 1517 77441 89600 0 .00
496 1421 72321 76800 0 .00
731 2640 94721 102400 0 .00
803 2385 82433 89600 0 .00
... output truncated ...
From the output you can see that RMAN didn't skip any blocks at the Cell level. You might ask if it means
the Exadata software was not effective enough. Actually the blocks read by the RMAN channel (shown under
BLOCKS_READ) are less than total blocks of the data file (DATAFILE_BLOCKS). So RMAN did perform some type
of filtering. However, that filtering did not occur at the Cell level. To understand the reason for these results, see the
How It Works section below.
How It Works
Before explaining the cause of the behavior shown in the Solution, let us explain some relevant columns of the view
V$BACKUP_DATAFILE. Take a look at Table
25-1
.
