False increase of 'Global Cache Blocks Lost' or 'gc blocks lost' after upgrade to 12c
(Doc ID 2096299.1)
Last updated on JUNE 18, 2023
Applies to:
Oracle Database - Enterprise Edition - Version 12.1.0.2 to 12.1.0.2 [Release 12.1]Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Information in this document applies to any platform.
Symptoms
'gc blocks lost' increases after 12c Upgrade, we can see:
1. Statistic increases constantly:
SELECT A.INST_ID "INSTANCE", A.VALUE "GC BLOCKS LOST",
B.VALUE "GC CUR BLOCKS SERVED",
C.VALUE "GC CR BLOCKS SERVED",
A.VALUE/(B.VALUE+C.VALUE) RATIO
FROM GV$SYSSTAT A, GV$SYSSTAT B, GV$SYSSTAT C
WHERE A.NAME='gc blocks lost' AND
B.NAME='gc current blocks served' AND
C.NAME='gc cr blocks served' and
B.INST_ID=a.inst_id AND
C.INST_ID = a.inst_id
/
<< 12.1.0.2>
11:02:14 SQL> /
INSTANCE GC BLOCKS LOST GC CUR BLOCKS SERVED GC CR BLOCKS SERVED RATIO
---------- -------------- -------------------- ------------------- ----------
1 573 79063 36031 .004978539
2 337 36154 63131 .003394269
11:07:03 SQL> /
INSTANCE GC BLOCKS LOST GC CUR BLOCKS SERVED GC CR BLOCKS SERVED RATIO
---------- -------------- -------------------- ------------------- ----------
1 573 79084 36112 .004974131
2 338 36176 63181 .003401874
<< 11.2.0.3>>
11:02:52 SQL> /
INSTANCE GC BLOCKS LOST GC CUR BLOCKS SERVED GC CR BLOCKS SERVED RATIO
---------- -------------- -------------------- ------------------- ----------
1 0 7687 49 0
2 0 34 33 0
11:07:13 SQL> /
INSTANCE GC BLOCKS LOST GC CUR BLOCKS SERVED GC CR BLOCKS SERVED RATIO
---------- -------------- -------------------- ------------------- ----------
2 0 36 55 0
1 0 7696 49 0
2. If EM is used you may see alerts produced like:
Target type=Database Instance
Target name=<target name>
Categories=Error
Message=Metrics Global Cache Blocks Lost is at 4
Severity=Warning
Event reported time=Apr 2, 2015 2:50:27 AM CDT
Operating System=Linux
Platform=x86_64
Associated Incident Id=298857
Associated Incident Status=New
Associated Incident Owner=
Associated Incident Acknowledged By Owner=No
Associated Incident Priority=None
Associated Incident Escalation Level=0
Event Type=Metric Alert
Event name=rac_global_cache:lost
Metric Group=Global Cache Statistics
Metric=Global Cache Blocks Lost
Metric value=4
Key Value=
Rule Name=Database Availability and Critical States <DBA_owner>,Metric Alerts
Event Rule
Rule Owner=<DBA_owner>
Update Details:
Metrics Global Cache Blocks Lost is at 4
Changes
Customer upgrade from 11.2.0.3 to 12.1.0.2
Cause
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In this Document
Symptoms |
Changes |
Cause |
Solution |
References |