Holger Rehn created DERBY-7109:
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Summary: SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE doesn't work as
expected
Key: DERBY-7109
URL: https://issues.apache.org/jira/browse/DERBY-7109
Project: Derby
Issue Type: Bug
Components: Store
Affects Versions: 10.15.2.0, 10.14.2.0
Reporter: Holger Rehn
The SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE procedure seems to be unable to
reclaim any disk space under almost all circumstances. I have a number of
existing DBs that I tried to reorganize to reclaim disk space using the
mentioned procedure. Because that didn't even free the smallest amount of
space, I started a number of tests and it looks like inplace compression simply
doesn't work, at all.
Example:
One of the DBs uses ~37 GB of disk space and the exact same amount after
running SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE. After using
SYSCS_UTIL.SYSCS_COMPRESS_TABLE to reorganize the DB it only uses 20,4 GB of
disk space. This might be correct, if I correctly understand how inplace
compression should work - but is not really what I expected. But even after I
completely deleted a number of tables and removed more than 90% of the rows
from all other tables of the original DB,
SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE was unable to reclaim any disk space.
In contrast, SYSCS_UTIL.SYSCS_COMPRESS_TABLE now reduced the DB size to ~
130MB. To carry this to the extreme, I completely removed any data from all
tables. As expected, procedure SYSCS_UTIL.SYSCS_COMPRESS_TABLE now results in
an empty DB only taking up ~4 MB of disk space, while
SYSCS_UTIL.SYSCS_INPLACE_COMPRESS_TABLE was still unable to reclaim a relevant
amount of disk space (only ~ 600MB), leaving a completely empty DB still
occupying more than 30 GB of disk space.
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