 Oracle
Tips by BurlesonOracle 10g
Easier Transaction Recovery Monitoring
During the second phase of
instance recovery, Oracle rolls back uncommitted
transactions. Oracle uses two methods: 'Fast-start on-demand
rollback' and 'fast-start parallel rollback'. Together,
these two features help to increase the efficiency of the
recovery phase.
Using the fast-start
on-demand rollback feature, the required transaction's
recovery is handled first. If a user attempts to access a
row that is locked by a terminated transaction, Oracle rolls
back only those changes necessary to complete the
transaction; in other words, it rolls them back on demand.
Consequently, new transactions do not have to wait until all
parts of a long transaction are rolled back.
In the fast-start parallel
rollback method, the background process SMON acts as a
coordinator and rolls back a set of transactions in parallel
using multiple server processes. This feature is
particularly useful when a system has transactions that run
a long time before committing, especially parallel INSERT,
UPDATE, and DELETE operations. SMON automatically decides
when to begin parallel rollback and disperses the work among
several parallel processes.
You can monitor the progress
of fast-start parallel rollback by examining the
v$fast_start_servers and v$fast_start_transactions views.
v$fast_start_servers provides information about all recovery
processes performing fast-start parallel rollback.
v$fast_start_transactions contains data about the progress
of the transactions.
There are three new columns
in the 10g release that assist monitoring. They are XID,
PXID, and RCVSERVERS, as shown in the description below.
SQL> desc V$FAST_START_TRANSACTIONS
Name Null? Type
---------------------------- -------- ------------
USN NUMBER
SLT NUMBER
SEQ NUMBER
STATE VARCHAR2(16)
UNDOBLOCKSDONE NUMBER
UNDOBLOCKSTOTAL NUMBER
PID NUMBER
CPUTIME NUMBER
PARENTUSN NUMBER
PARENTSLT NUMBER
PARENTSEQ NUMBER
XID RAW(8)
PXID RAW(8)
RCVSERVERS NUMBER
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