Re: DBWR write chunk

Things have changed since 8.0.5, I see now that the thing I was referring to was

    kcbswc - DBWR max outstanding writes (8.1 version) formerly known as

    kcbswc - DB writer IO clump. (8.0 version)

But Oracle 8.1 has introduced

    kcbscw - DBWR write chunk.

However, kcbswc as was had two functions - one to limit the number of blocks that were allowed to be dirty and the other to specify the number of blocks that DBWR would attempt to write.

i.e. 8.0 used to work on the basis that DBWR had to write if it found kcbswc blocks dirty, and the number of blocks it had to try to write if cued was also kcbswc, and this used to default (sometimes through bugs) to a very large value and cause DBWR to get too busy.

I think that these two functions have now been separated: DBWR has to write if it finds that kcbswc blocks are dirty, but the number of blocks that may be written at any one time is limited to the smaller kcbscw value.

As you indicate, _db_block_write_batch has disappeared in 8.1 to be split into two parameters corresponding to the two x$kvii tags.

Thanks for the update.

--
Jonathan Lewis
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Andrew Mobbs wrote in message ...


>Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote:

>>

>>This is the number of blocks that dbwr

>>will attempt to find and write when called

>>by a process that needs some buffers

>>freed.  It does not imply anything about

>>continuous buffers, or single write sizes.

>>

>>In some versions of Oracle, it can be set

>>by the value of _db_block_write_batch.

>

>I thought that "DBWR write chunk" was the number of writes that DBWR

>would wait to return before putting the blocks from those writes back on

>the LRU lists.

>

>It can be set (in 8.1.6 at least) by _db_writer_chunk_writes

>

>Andrew.

>

>--

>Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/