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List:       hsqldb-user
Subject:    [Hsqldb-user] =?utf-8?q?Interpreting_SYSTEM=5FCACHEINFO=2EFILE=5F?= =?utf-8?q?LOST=5FBYTES_for_CACHE
From:       xavier.bruggheman () stepinfo ! com
Date:       2014-08-06 17:20:42
Message-ID: a85855fb082918008a0f8453d0e852bf () stepinfo ! com
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Hi,

I'm embedding HSQLDB v2.3.2 in an application, and I'm trying to use the 
FILE_LOST_BYTES column to determine the amount of wasted space and the 
percentage of fragmentation of my cache file and trigger either a 
CHECKPOINT DEFRAG or SHUTDOWN COMPACT on the embeded database during 
application startup when above a configurable percentage or amount.
I'm doing this on application startup rather than using the "SET FILES 
DEFRAG" statement to avoid the database going down for a relatively long 
time (DB is a couple of GBs) at unpredictable moments while the 
application is running.

The issue I'm having is that I'm getting weird values in the 
FILE_LOST_BYTES column after a day or two of mixed reads and 
insert/update/delete activity. The values in this column grow very large 
and above the actual .data file size, most of the time thousands of time 
bigger than it, and very much above the capacity of the disk hosting the 
database (600 TB...).

For reference, the query I'm using:
SELECT CACHE_FILE, FILE_LOST_BYTES FROM 
INFORMATION_SCHEMA.SYSTEM_CACHEINFO

Is there something I'm missing ? Maybe the unit for the column isn't 
BYTES as the column name implies, or is there something wrong with the 
way this information is made available in the information schema ?

Best regards,

Xavier BRUGGHEMAN

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