Re: Does a commit cause a checkpoint?

On Thu, 19 Jun 2003 00:41:45 GMT, Hans Forbrich <forbrich_at_telusplanet.net> wrote:

A logswitch causes a checkpoint which causes LGWR to flush the redo log buffer, but no change in SCN

A checkpoint causes the DBWn to write to file, and also causes the LGWR to flush the redo buffer, but no change in SCN

>
>
>Peter wrote:
>
>> Does a commit cause a checkpoint?
>>
>> A checkpoint causes the SCN to increment. A logswitch causes a
>> checkpoint and threrefore a SCN incremental change.
>> What I am confused about is whether a commit causes a checkpoint and
>> therefoe a SCN increment.
>>
>
>From the "Oracle9i Database Administrator's Guide, Release 2 (9.2), Part
>Number A96521-01" at
>http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96521/onlineredo.htm#ADMIN007
>in Chapter 7, "Managing the Online Redo Log", in section titled "Online
>Redo Log Contents",
>
>the second paragraph reads:
>
>>>>>>>>
>Redo records are buffered in a circular fashion in the redo log buffer
>of the SGA (see "How Oracle Writes to the Online Redo Log") and are
>written to one of the online redo log files by the Oracle background
>process Log Writer (LGWR). Whenever a transaction is committed, LGWR
>writes the transaction's redo records from the redo log buffer of the
>SGA to an online redo log file, and a system change number (SCN) is
>assigned to identify the redo records for each committed transaction.
>Only when all redo records associated with a given transaction are
>safely on disk in the online logs is the user process notified that the
>transaction has been committed.
><<<<<<<
>
>Please note the sentance starting with "Whenever a transaction is
>committed,"
>
>(I'm still wondering what is your documentation source - whatever it is
>seems to be leaving huge gaps in your understanding)
>
>/Hans
>
>>
>> Thanks
Received on Wed Jun 18 2003 - 21:04:50 CDT