Re: snapshots

I was thinking of this:

You have a table which is being snapshotted periodically to an instance on another server. You delete a couple of records from the table, commit, and move on with your life. A while later, the periodic snapshot fires up, scans the mlog$ table, and retrieves the rowid for the deleted records. So what does it do with them? You can't just pass rowid's to the other instance -- they're not valid across instances. You need the PK values to determine what was deleted on the master. You can't get them from the master table, because the record has been deleted and long since committed. Perhaps the PK values are saved in the mlog$ table for deletes?

At 02:16 PM 1/12/01 -0800, you wrote:
>Dennis,
> I would think since the snap$ table has the rowid
>value that when a delete needs to be performed it
>would delete using the rowid.
>
>James
>--- Dennis Taylor <ismgr_at_pctc.com> wrote:
>> At 10:06 AM 1/12/01 -0800, you wrote:
>> >hi list
>> >
>> >would any refresh of a snapshot fire a query
>> against the base table?
>> >
>> > i think its supposed to go against the mlog$ table
>> of the base table. we
>> >have a situation where there is a poor-performing
>> query that is fired at
>> >exact intervals accessing the base table and no
>> application seems to be
>> >firing it?
>>
>> The mlog$ table only contains a couple of fields,
>> one of which is the ROWID
>> of the affected record, and another is the dml
>> operation (insert, delete,
>> update). I'd assume that the snapshot update uses
>> this info to go get the
>> affected record (unless it's a delete) from the base
>> table.
>>
>> This is weird when you think of it. It implies that
>> the snapshot process is
>> able to get "old" information, i.e. the record from
>> before the delete, so
>> that it can grab the PK info. Or am I missing
>> something?
>>
>>
>> Dennis Taylor
>> --------------------------------
>> Save the plankton - nuke the whales!
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Received on Fri Jan 12 2001 - 18:01:32 CST