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https://issues.apache.org/jira/browse/DERBY-4525?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844696#action_12844696
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Kim Haase commented on DERBY-4525:
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Well, the wrong-format error message may not be that serious an issue. But it
does seem to be the case that you can drop an on-disk database, at least if you
create it in a directory called "memory".
I (accidentally, because of a punctuation error) create a db called myDB in the
directory memory:
ij> connect 'jdbc:derby://localhost:1527/memory/myDB;create=true';
ij> create table t(c int);
0 rows inserted/updated/deleted
The database is visible in the file system:
ls ~/DERBYTUTOR/*
/home/chaase/DERBYTUTOR/derby.log
/home/chaase/DERBYTUTOR/firstdb:
log/ seg0/ service.properties
/home/chaase/DERBYTUTOR/memory:
myDB/
/home/chaase/DERBYTUTOR/seconddb:
log/ seg0/ service.properties
The database is actually there:
ls ~/DERBYTUTOR/memory/myDB
db.lck log/ service.properties
dbex.lck seg0/ tmp/
I am then able to drop this database even though it's a file system db:
ij> connect 'jdbc:derby://localhost:1527/memory/myDB;drop=true';
ERROR 08006: DERBY SQL error: SQLCODE: -1, SQLSTATE: 08006, SQLERRMC: Database
'memory/myDB' dropped.
The database is gone:
ls ~/DERBYTUTOR/*
/home/chaase/DERBYTUTOR/derby.log
/home/chaase/DERBYTUTOR/firstdb:
log/ seg0/ service.properties
/home/chaase/DERBYTUTOR/memory:
/home/chaase/DERBYTUTOR/seconddb:
log/ seg0/ service.properties
I then try to drop another filesystem db, one that doesn't have "memory" in the
name. This fails, as it should:
ij> connect 'jdbc:derby://localhost:1527/seconddb;drop=true';
ERROR XBM0I: DERBY SQL error: SQLCODE: -1, SQLSTATE: XBM0I, SQLERRMC: Directory
seconddb cannot be removed.
I then use the correct syntax to create the in-memory db. It is created, but in
a new connection.
ij> connect 'jdbc:derby://localhost:1527/memory:myDB;create=true';
ij(CONNECTION1)> show connections;
CONNECTION0 - jdbc:derby://localhost:1527/memory/myDB;create=true
CONNECTION1* - jdbc:derby://localhost:1527/memory:myDB;create=true
* = current connection
I find that if I start over and create the filesystem db, I can shut it down
and it stays there:
ij> connect 'jdbc:derby://localhost:1527/memory/myDB;create=true';
ij> connect 'jdbc:derby://localhost:1527/memory/myDB;shutdown=true';
ERROR 08006: DERBY SQL error: SQLCODE: -1, SQLSTATE: 08006, SQLERRMC: Database
'memory/myDB' shutdown.
ls ~/DERBYTUTOR/memory
myDB/
This is as it should be. I shouldn't be able to drop it, though.
> Document the in-memory storage back end
> ---------------------------------------
>
> Key: DERBY-4525
> URL: https://issues.apache.org/jira/browse/DERBY-4525
> Project: Derby
> Issue Type: Task
> Components: Documentation
> Affects Versions: 10.6.0.0
> Reporter: Kristian Waagan
> Assignee: Kim Haase
> Fix For: 10.6.0.0
>
>
> The in-memory back end isn't considered experimental anymore, we have to
> write user documentation for the feature(s).
> I'm not sure how it should be structured, and where the content should be
> added.
> Just as a rough cut, here are a few possible topics (I'm not sure if all
> should be included or not):
> - documenting the new protocol name ('memory')
> - documenting the new 'drop' JDBC connection URL attribute
> - describing the limitations of the feature (all your data will be lost
> if..., how to use it with the client driver and the data sources)
> - "advanced use" (pull dbs on disk into memory, backup in-memory dbs to disk)
> - tuning tips (there are some issues with extreme page cache sizes, maybe the
> existing content on page size is valid)
> - known problems (nothing concrete here yet, but we have one inquiry about
> disappearing databases - the current theory is that different class loaders
> are used)
> Some more information is available at
> http://wiki.apache.org/db-derby/InMemoryBackEndPrimer
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