Re: SECUREFILES disaster

From: Mark D Powell <>
Date: Mon, 23 Apr 2012 06:33:20 -0700 (PDT)
Message-ID: <6124715.1626.1335188000775.JavaMail.geo-discussion-forums_at_ynee1>

On Sunday, April 22, 2012 3:24:27 PM UTC-4, Mladen Gogala wrote:
> On Sun, 22 Apr 2012 19:20:39 +0000, Mladen Gogala wrote:
> > e level locking, with predictably disastrous effects on concurrency. LOB
> > columns are not relational data, they're stored within a LOB segment
> > like files in a directory, but the directory operations are conducted
> > without doing the space accounting, which means that there will be a lot
> > of wasted space.
> BTW, space management, if that can be called that way, uses only high
> water mark after inserts. That's all that I was able to confirm.
> --

Just some general comments

The LOB data type has never been known for its space efficiency. In the environemts where we have used LOB datatypes update to the LOB data has been rare so we have not suffered heavy excessive space usage though I have seen some. With traditional LOB data types now referred to as basic files by Oracle the chunk size was very important in relation to space usage since the chunk size was the smallest unit of space allocated to a LOB operation.

Concurrent update to the LOB data has been pretty much non-existent in my experience.

If you have an environment where the LOB column itself is not just updated but is subject to concurrent update then it may be worth looking into what the LOB data consists of. You may find that a better design than using a single LOB column for the data might be using multiple LOB columns. The multiple LOB columns might take the form of separate LOB columns each holding a portion of the existing data that serves a specific purpose or involve some form of versioning so that multiple rows exist where new versions of the data result in new rows in the table. Potentially old versions or old enough versions could be purged freeing entire LOB's allowing better reuse of LOB space.

But then changing the design after the fact is rarely an easy sell even when the proposal makes sense.

HTH -- Mark D Powell -- Received on Mon Apr 23 2012 - 08:33:20 CDT

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