RE: truncating snapshots

From: Henry Poras <Henry.Poras_at_ctp.com>
Date: Mon, 17 Sep 2001 09:20:50 -0700
Message-ID: <F001.00390561.20010917075019@fatcity.com>

Guess I wasn't too clear. Here's the scoop (there is probably a much easier way to do this, but I just can't get there from here). There is a 10million row table on a remote database. Each week, there is a change in about 5-10,000 rows (inserts). Currently this table is brought over to a local database. A convoluted query is then run to keep our developers happy and the result set is entered into another table. The query, though convoluted, does not use any aggregate functions, just a mess of joins. Right now this query is run on the complete 10 million row table brought over from the remote database. What I would like to do is to run the query on just the new rows, appending this result to the existing data. Since the snapshot log used for a fast refresh already keeps track of this for me I thought it might be a nice way to go. (I guess I could always flip a flag field, but why do extra work if Oracle already does it for me?)

So my plan was to create a procedure which will manually take a fast refresh, run the query, check for success, truncate the table underlying the snapshot view. Since the underlying structure is just a table, and the master log data transfer is strictly in one direction, it looks like it should work, but are there any gothchas? It seems to be OK on a test system.

Thanks again.

Henry

-----Original Message-----
Sent: Sunday, September 16, 2001 9:38 AM To: ORACLE-L_at_fatcity.com; Henry Poras

Henry,

I'm not sure what you're trying to accomplish by truncating the snapshot. The whole point of the refresh process is to keep the snapshot in sync with the master site.

Presumably you are doing a CTAS off of the snapshot to do your manipulations, so what is the point in truncating the snapshot? I don't have a db handy to test whether Oracle detects that the snapshot has been truncated and does a complete refresh, but if the snapshot is very large it would probably be faster to drop and recreate it than to do a complete refresh.

A more detailed explanation of the process would help.

HTH,

• Anita
  • Henry Poras <Henry.Poras_at_ctp.com> wrote:
    > !! Please do not post Off Topic to this List !!
    >
    > I need to move the changes in a table from one
    > database to another. It
    > seemed that fast snapshots would be a good way to do
    > this as the database
    > will automatically keep track of the changes for me.
    > The question is that
    > once I move the data to the snapshot side, I need to
    > manipulate it, move it
    > into another table, and start the cycle again. This
    > means truncating the
    > snapshot between refreshes. I tried this on a test
    > system and it seesm to
    > work, but I don't think Oracle supports it. I don't
    > want updatable snapshots
    > as this is strictly one way movement of data. Has
    > anyone else tried this?
    > Are there any potential problems? I think I am just
    > truncating a table
    > underlying the snapshot view so I don't see what
    > could go wrong.
    >
    > Thanks.
    >
    > Henry
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    > Author: Henry Poras
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Author: Henry Poras
  INET: Henry.Poras_at_ctp.com

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Received on Mon Sep 17 2001 - 11:20:50 CDT