[jira] [Commented] (IGNITE-8100) jdbc getSchemas method could miss schemas for not started remote caches

["Vladimir Ozerov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IGNITE-8100?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16566437#comment-16566437 ] 

Vladimir Ozerov commented on IGNITE-8100:
-----------------------------------------

[~ilyak], [~pkouznet], [~tledkov-gridgain],

Proposed patch fixes original problem, but its implementation may lead to massive overhead on the whole cluster. Caches are not started on a client nodes until they are needed. When client node needs to start a cache it will send a discovery message. Then server nodes will register this client and it will participate in further exchanges, making them more heavy. 

At the same time there is a high chance that user will never use this cache and only need to fethc metadata. This is especially true for various third-party tools, which can eagerly list all database objects in UI. We definitely do not want to start potentially dozens of cache on a client just to do that. In addition, current implementation start caches one-by-one which may be really long thing.

Correct implementation should work as follows:
# When node is started, we should collect all known cache descriptors into some local collection under *write lock*
# When dynamic cache change request is received (i.e. cache is started or stopped) we should update this collection under *write lock* in *discovery thread*
# Schema changes ({{CREATE/DROP INDEX}} , {{ALTER TABLE}}) should be processed in the same way as p.2
# When metadata request from JDBC driver is received, we should iterate over collected descriptors and construct the result (e.g. list of schemas, list of indexes, etc) under *read lock*

Lock is necessary because descriptors may be changed from discovery thread leading to inconsistent JDBC results. Alternatively you may want to employ copy-on-write technique.

> jdbc getSchemas method could miss schemas for not started remote caches
> -----------------------------------------------------------------------
>
>                 Key: IGNITE-8100
>                 URL: https://issues.apache.org/jira/browse/IGNITE-8100
>             Project: Ignite
>          Issue Type: Bug
>            Reporter: Pavel Kuznetsov
>            Assignee: Ilya Kasnacheev
>            Priority: Major
>
> On jdbc side we have org.apache.ignite.internal.jdbc.thin.JdbcThinDatabaseMetadata#getSchemas(java.lang.String, java.lang.String)
> on the server side result is constructed by this:
> {noformat}
> for (String cacheName : ctx.cache().publicCacheNames()) {
>         for (GridQueryTypeDescriptor table : ctx.query().types(cacheName)) {
>             if (matches(table.schemaName(), schemaPtrn))
>                schemas.add(table.schemaName());
>         }
> }
> {noformat}
> see org.apache.ignite.internal.processors.odbc.jdbc.JdbcRequestHandler#getSchemas
> If we havn't started cache(with a table) on some remote node, we will miss that scheme.



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