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log file sync and block recovery from logseq

User_96XRQNov 5 2020

Hi all,
sometimes log file sync event spike on our 11.2.0.4 db on Solaris.
when we look at alert log at the same time we see following messages.

Block recovery from logseq 1462532, block 36595759 to scn 3522018885687
Recovery of Online Redo Log: Thread 1 Group 59 Seq 1462532 Reading mem 0
Mem# 0: +REDO/DBNAME/onlinelog/group_59.272.1047579261
Mem# 1: +REDO/DBNAME/onlinelog/group_59.356.1047581307
Block recovery completed at rba 1462532.36596324.16, scn 820.145702968
Block recovery from logseq 1462532, block 36594513 to scn 3522018885686
Recovery of Online Redo Log: Thread 1 Group 59 Seq 1462532 Reading mem 0
Mem# 0: +REDO/DBNAME/onlinelog/group_59.272.1047579261
Mem# 1: +REDO/DBNAME/onlinelog/group_59.356.1047581307
Block recovery completed at rba 1462532.36596324.16, scn 820.145702967

there is no message on lgwr trace and wait chains are below.

%This SECONDS AAS WAIT_CHAIN
------ ---------- ------- --------------------------------------------------------
32% 2985 96.3 -> log file sync -> LGWR wait for redo copy -> ON CPU
26% 2421 78.1 -> ON CPU
21% 1911 61.6 -> log file sync -> log file parallel write

Do you have reason for that?
Regards.

Comments

Jonathan Lewis

Do you see ANY trace files around the time of the event?
It looks like it might be a case of the buffered copy of a block being corrupt and Oracle doing an in-memory block recovery by reading the block from disc into the buffer cache than finding and applying any redo for that block to bring the buffer up to date.
If that's correct then it's possible there's an Oracle bug corrupting blocks occasionally, or you have a memory fault which is corrupting Oracle blocks.
Regards
Jonathan Lewis

UPDATE: The last couple of paragraphs of this note of mine make a few comments about the mechanism.

1 person found this helpful
Jonathan Lewis

Another follow-up (for the same blog note). If you read the conversation [starting at comment #9](https://jonathanlewis.wordpress.com/2010/12/31/quiz-night-11/#comment-39097) it suggests that your alert log ought to have some details about the corrupt block just before the bit you've supplied. (So it if doesn't there's presumably some other reason for what's going on.)

Regards
Jonathan Lewis

User_96XRQ

Hi Jonathan,
thanks for reply. We did not see any trace files at that time.
Regards.

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Added on Nov 5 2020
#11gr2, #general-database-discussions, #performance, #tuning
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