Re: using lobs system types to manually clear data

My only concern is that writing a lot of data would "stretch" the .lobs
file even larger as it grows to accommodate an artificially large quantity
of random data.   File size is a major concern since this is part of a
desktop application.  Is there some way to calculate exactly how much
random data I'd need to write to fill the unused areas of a given .lobs
file so I can eliminate or at least minimize further enlarging the .lobs
file?

Thanks for the help.

On Wed, May 21, 2014 at 2:22 PM, Fred Toussi <[email protected]>wrote:

>  It is easier to delete the rows that contain the lobs. The spaces then
> become available for new lobs after a checkpoint. Create a a table with a
> lob column and insert random data in multiples of 32 GB. This will fill up
> the space. Then delete rows from this table and finally perform a
> checkpoint to release the space again.
>
> The LOB_IDS table is for the currently existing lobs that have a
> reference, not deleted ones.
>
> Fred
>
> On Wed, May 21, 2014, at 18:38, Brian Young wrote:
>
> Hello, in our usage of hsqldb, it is sometimes necessary to permanently
> delete blobs such that someone "in the know" couldn't recover said blob
> from the .lobs file.
>
> I am considering reading the system tables and zero out the blocks that
> are identified as having no active references.  Obviously this would be
> done while the database is "offline", meaning the cleanup process is the
> owner and single user of the database.
>
> I am assuming LOB_IDS.LOB_LENGTH is in bytes, but how do I determine the
> offset a given LOB within the .lobs file?
>
> Are there any gotchas here?
>
> Thanks
>
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