Deleting/Shrinking HSQLDB lob files - blob

Question

We're using HSQLDB 2.3.2 and we would like to get rid of the file containing the LOB data. As it is taking a large amount of disk space.
We already changed our LOB columns to VARCHAR. So we don't have any LOB columns anymore.
$ ./execute_query.sh "SELECT TABLE_NAME, COLUMN_NAME, DATA_TYPE, TYPE_NAME FROM INFORMATION_SCHEMA.SYSTEM_COLUMNS WHERE TYPE_NAME LIKE '%LOB%';"
TABLE_NAME COLUMN_NAME DATA_TYPE TYPE_NAME
---------- ----------- --------- ---------
And a list of our HSQLDB files:
$ ls -hal
total 88G
drwxr-xr-x 3 admin admin 4.0K Sep 23 13:58 .
drwxr-xr-x 6 admin admin 4.0K Sep 1 09:27 ..
-rw-r--r-- 1 admin admin 1.5M Apr 9 01:13 hsqldb.jar
-rw-r--r-- 1 admin admin 2.9G Sep 23 13:53 hsqldb.db.data
-rw-r--r-- 1 admin admin 16 Sep 23 14:02 hsqldb.db.lck
-rw-r--r-- 1 admin admin 84G Aug 25 01:52 hsqldb.db.lobs
-rw-r--r-- 1 admin admin 70 Sep 23 14:00 hsqldb.db.log
-rw-r--r-- 1 admin admin 85 Sep 23 13:58 hsqldb.db.properties
-rw-r--r-- 1 admin admin 1.5G Sep 23 13:53 hsqldb.db.script
drwxr-xr-x 2 admin admin 4.0K Sep 23 13:54 hsqldb.db.tmp
We would like to get rid of the large hsqldb.db.lobs file.
After removing the file, the database does start correctly and seems to run fine. And I can run queries.
But after creating a table with LOB columns and adding data to them the hsqldb.db.lobs file gets created again with the original size (although it's a sparse file).
I suspect more magic can be done by modifying certain table values in the SYSTEM_LOBS schema. But I don't think that is a very good practice.
So what's the advised way to either
Shrink the LOB file so it is much smaller (as we don't use the data)
Remove the LOB file completely

Answer 1

After removing the file, the database does start correctly and seems
to run fine. And I can run queries.
At this point you need to perform CHECKPOINT to reset the lob tables. This works after a workaround described in this post (ignore the compressed setting):
HSQLDB: enable LOB compression for existing database