Re: database buffer cache / SGA

Thanks Thomas

So I was correct that if 1 block actually contains 8 rows, all 8 rows are read into memory. The system puts a general lock on the table and an exclusive lock on the block? If this is true and someone wants one of the rows that were read into buffer cache, does the system wait for the first transaction to be finished before it can get this additional row?

As to your statement that only bytes are recorded as changed, could you explain how that works or point me to a text that would do so.

Thanks for your help.

Thomas Kyte wrote:
>
> In article <3B577825.1BB18144_at_att.net>, stevek says...
> >
> >Oracle server receives a request from a client, run sql through sqlarea
> >in cache, if there runs,if not runs through plan process then executes,
> >if data in buffer cache uses that data otherwise get block(s) from
> >tablespace.
> >
> >Question: oracle deals with data in blocks only, block 8K, record 1K.
> >Does oracle take 7 additional records on the block read? Does it use the
> >same block size/number of records when it puts changed data in redo logs
> >and rbs?
>
> data is cached in blocks, you get the block cached, even if you want just 1 of
> the rows on that block.
>
> redo -- changed bytes (not even entire rows), unless the tablespace is in HOT
> backup mode then the first time a block is modified the entire block is written
> to redo and then changed bytes only after that.
>
> rollback -- changed bytes only.
>
> --
> Thomas Kyte (tkyte@us.oracle.com) http://asktom.oracle.com/
> Expert one on one Oracle, programming techniques and solutions for Oracle.
> http://www.amazon.com/exec/obidos/ASIN/1861004826/
> Opinions are mine and do not necessarily reflect those of Oracle Corp
Received on Fri Jul 20 2001 - 06:27:43 CDT