[jira] Commented: (DERBY-393) Allow multiple JVMs to have read-only access to the same directory-based database

["Eric Sirianni (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854451#action_12854451 ] 

Eric Sirianni commented on DERBY-393:
-------------------------------------

The Derby Developer's Guide states:

Corruption can occur even if one of the two booting systems has "readonly" access to the database.
(http://db.apache.org/derby/docs/10.5/devguide/cdevdvlp20458.html)

So does the above proposal of accessing the database via a new DirStorageFactory subclass that returns true for "isReadOnlyDatabase" do the trick?  Alternatively, does the documentation need to be updated?

I agree it would be very useful to have read-only access to a directory-based database that is booted as writable by a different JVM.  Consider the common use case of using 'ij' to do some read-only SQL queries while the application that is writing the derby DB is still running...

> Allow multiple JVMs to have read-only access to the same directory-based database
> ---------------------------------------------------------------------------------
>
>                 Key: DERBY-393
>                 URL: https://issues.apache.org/jira/browse/DERBY-393
>             Project: Derby
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Trejkaz
>         Attachments: readonly.patch
>
>
> For an application I'm building, we needed to permit multiple JVMs to access the same database.
> We couldn't easily use a network server configuration, as it would be difficult to figure out who to connect to since either user might want to view the database while the other database is offline.
> We couldn't just dump all the data in a JAR file, as our databases often end up being several gigabytes in size.
> So what we really need is a version of the directory store which is treated as if it were read-only.

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