RE: Query Database while shutdown in progress
- From: <Joel.Patterson@xxxxxxxxxxx>
- To: <randyjo@xxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 29 Jun 2007 07:31:31 -0400
OK, I give... bad morning for a Friday. I'm reading that you said
every 3 seconds... then you reply back apologizing for replying from
memory and accompany that with documentation that says every 3 seconds?
- and use an arrow to highlight the line.
I definitely cannot walk away missing this, so I apologize if my brain
hasn't kicked in yet... got a few things happening already this morning.
Joel Patterson
Database Administrator
joel.patterson@xxxxxxxxxxx
x72546
904 727-2546
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Randy Johnson
Sent: Thursday, June 28, 2007 7:30 PM
To: 'oracle-l'
Subject: RE: Query Database while shutdown in progress
Okay, I stand corrected. That's what happens when you reply from memory.
My bad.
CHECKPOINT TUNING AND ERROR HANDLING
1. What is a Checkpoint?
A Checkpoint is a database event which synchronizes the modified data
blocks in memory with the datafiles on disk. It offers Oracle the means
for ensuring the consistency of data modified by transactions. The
mechanism of writing modified blocks on disk in Oracle is not
synchronized with the commit of the corresponding transactions.
A checkpoint has two purposes: (1) to establish data consistency,
and (2) enable faster database recovery. How is recovery faster?
Because all database changes up to the checkpoint have been recorded in
the datafiles, making it unnecessary to apply redo log entries prior to
the checkpoint. The checkpoint must ensure that all the modified buffers
in the cache are really written to the corresponding datafiles to avoid
the loss of data
which may occur with a crash (instance or disk failure).
Oracle writes the dirty buffers to disk only on certain conditions:
- A shadow process must scan more than one-quarter of the
db_block_buffer
parameter.
- Every three seconds. <----<<
- When a checkpoint is produced.
A checkpoint is realized on five types of events:
- At each switch of the redo log files.
- When the delay for LOG_CHECKPOINT_TIMEOUT is reached.
- When the size in bytes corresponding to :
(LOG_CHECKPOINT_INTERVAL* size of IO OS blocks)
is written on the current redo log file.
- Directly by the ALTER SYSTEM SWITCH LOGFILE command.
- Directly with the ALTER SYSTEM CHECKPOINT command.
During a checkpoint the following occurs:
- The database writer (DBWR) writes all modified database
blocks in the buffer cache back to datafiles,
- Log writer (LGWR) updates both the controlfile and
the datafiles to indicate when the last checkpoint
occurred (SCN)
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Jared Still
Sent: Thursday, June 28, 2007 1:46 PM
To: randyjo@xxxxxxxxxxxxx
Cc: oracle-l
Subject: Re: Query Database while shutdown in progress
On 6/27/07, Randy Johnson <randyjo@xxxxxxxxxxxxx> wrote:
BTW, unless I'm mistaken, checkpoints occur automatically at the least
every 3 seconds.
Gee, I hope not.
LGWR on the other hand... :)
--
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
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