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From "Kim Haase (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4525) Document the in-memory storage back end
Date Fri, 12 Mar 2010 23:31:27 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4525?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844754#action_12844754

Kim Haase commented on DERBY-4525:

I wonder if we need to say anything about what connection attributes work with the in-memory
db and which don't. I think in most cases it would be intuitive -- attributes having to do
with replication wouldn't, would they? I would think most others would.

One that I would expect to work doesn't though -- databaseName. When I'm in ij, I can create
an in-memory db, disconnect, and then connect again, and the db is still there. I can connect
to it the usual way, but not using the databaseName attribute -- I tried a couple of different

ij> connect 'jdbc:derby:memory:myDB;create=true';
ij> create table t(c int);
0 rows inserted/updated/deleted
ij> disconnect;
ij> connect 'jdbc:derby:memory:myDB';
ij> insert into t values(1), (2);
2 rows inserted/updated/deleted
ij> select * from t;

2 rows selected
ij> disconnect;
ij> connect 'jdbc:derby:memory;databaseName=myDB';
ERROR XJ004: Database 'memory' not found.
ij> connect 'jdbc:derby:memory:;databaseName=myDB';
ERROR XJ004: Database 'memory:' not found.

> 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:
>            Reporter: Kristian Waagan
>            Assignee: Kim Haase
>             Fix For:
> 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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