My Oracle Support Banner

Poor RMAN SBT Restore Performance: RMAN does not parallelize despite allocating >1 Channel (Doc ID 433335.1)

Last updated on OCTOBER 31, 2016

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 10.1 to 10.2]
Information in this document applies to any platform.
***Checked for relevance on 16-Apr-2014***


RMAN 10gR2 restore and recover using TAPE incremental level 1 backups does NOT apply the
incrementals in parallel. Despite having allocated multiple channels RMAN only uses a single
channel for the restore hence the RECOVER phase takes much longer to complete. This is changed
behaviour from 9i where the restore always used all allocated channels .  

This issue may occur during full database restore also.

RMAN debug trace shows that we:

a. validate each backuppiece to be restored in turn:

DBGPLSQL: channel TAPE_CHAN_1: validated handle:P30<P30_1254:621459123>.incr1
Media:0a01032f:42d58c3d:7290:0006[[M00306L3] E7-oracle8_188] attributes=0 msca=0 [14:22:12.813](val_pieces)
DBGPLSQL: channel TAPE_CHAN_1: validated handle:P30<P30_1252:621459123>.incr1
Media:0a01032f:42d58c3d:7290:0006[[M00306L3] E7-oracle8_188] attributes=0 msca=0 [14:22:12.847](val_pieces)

b. Then we generate one jobstep PER incremental backuppiece to be restored:

DBGPLSQL: 1 STEP id=1 status=NOT STARTED devtype=SBT_TAPE bs.stamp=621459134 step_size=0 Bytes
DBGPLSQL: 2 STEP id=2 status=NOT STARTED devtype=SBT_TAPE instid=1
DBGPLSQL: 3 STEP id=3 status=NOT STARTED devtype=DISK instid=1
DBGPLSQL: 4 STEP id=4 status=NOT STARTED devtype=SBT_TAPE bs.stamp=621459144 step_size=0 Bytes
DBGPLSQL: 5 STEP id=5 status=NOT STARTED devtype=SBT_TAPE bs.stamp=621459177 step_size=0 Bytes
DBGPLSQL: 12 STEP id=12 status=NOT STARTED devtype=SBT_TAPE bs.stamp=621459387 step_size=0 Bytes

c. But we are only able to run one step at a time:

DBGRPC: krmqgns: channel TAPE_CHAN_2 could not find any other channel to
run step 4, trying anyway (krmqgns)
DBGMISC: channel TAPE_CHAN_2 could not lock media [0a01032f:42d58c3d:7290:
0006[[M00306L3] E7-oracle8_188]] [14:22:12.912] (krmqgns)

Each channel in turn attempts to run steps 4-12 but fails with "could not lock media".


To view full details, sign in with your My Oracle Support account.

Don't have a My Oracle Support account? Click to get started!

In this Document

This document is being delivered to you via Oracle Support's Rapid Visibility (RaV) process and therefore has not been subject to an independent technical review.
My Oracle Support provides customers with access to over a million knowledge articles and a vibrant support community of peers and Oracle experts.