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https://issues.apache.org/jira/browse/HBASE-10584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13909722#comment-13909722
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Feng Honghua commented on HBASE-10584:
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bq.We need a new issue after this one? There should be a general prescription
on how to avoid our doing table-state transitions that by-pass each other
thereby going forward? Should all queries about the state of tables
(enabled/disabled) go via the master from here on out? If so, what to
deprecate? (Can be different issue)
Agree on 'There should be a general prescription on how to avoid our doing
table-state transitions that by-pass each other thereby going forward' and 'All
queries about the state of tables (enabled/disabled) go via the master from
here on out'. We can come up with a general prescription and then do a
comprehensive review of existing code to ensure/enforce the consistency.
We can use a separate more general jira for this purpose(plays as a central
placeholder for sub-tasks for individual outside inconsistency), it's about the
consistency from the outside perspective of client, it is different from the
master's current internal inconsistency due to missed events resulted from
misusing zk's watch/notify mechanism for state-machine maintenance and
maintaining truth in multiple places.
Opinion?
> Inconsistency between tableExists and listTables in implementation
> ------------------------------------------------------------------
>
> Key: HBASE-10584
> URL: https://issues.apache.org/jira/browse/HBASE-10584
> Project: HBase
> Issue Type: Bug
> Components: Client, master
> Reporter: Feng Honghua
> Assignee: Feng Honghua
> Attachments: HBASE-10584-trunk_v1.patch, HBASE-10584-trunk_v1.patch
>
>
> # HBaseAdmin.tableExists is implemented by scanning meta table
> # HBaseAdmin.listTables(and HBaseAdmin.getTableDescriptor) is implemented by
> talking with HMaster which responses by querying the FSTableDescriptors, and
> FSTableDescriptors return all tables by scanning all the table descriptor
> files in FS(cache also plays here, so most of time it can be satisfied by
> cache)...
> Actually HBaseAdmin requests HMaster to check if a table exists internally
> when implementing deleteTable(see below), then why does it use a
> different(scanning meta table) way to implementing tableExists() for outside
> user to use for the same purpose?
> {code}
> tableExists = false;
> GetTableDescriptorsResponse htds;
> MasterKeepAliveConnection master = connection.getKeepAliveMasterService();
> try {
> GetTableDescriptorsRequest req =
> RequestConverter.buildGetTableDescriptorsRequest(tableName);
> htds = master.getTableDescriptors(null, req);
> } catch (ServiceException se) {
> throw ProtobufUtil.getRemoteException(se);
> } finally {
> master.close();
> }
> tableExists = !htds.getTableSchemaList().isEmpty();
> {code}
> (Above verifying that table descriptor file is deleted can guarantee all
> items of this table are deleted from meta table...)
> Since creating table descriptor files and inserting item to meta table occur
> in different time without atomic semantic, this inconsistency in
> implementation can lead to confusing behaviors when create-table or
> delete-table fails midway, (before according cleanup is done) table
> descriptor file may exists while no item exists in meta table (for
> create-table where table descriptor file is created before inserting item to
> meta table), this leads to listTables including that table, while tableExists
> says no. Similar inconsistency if delete-table fails mid-way...
> Confusing behavior can happen during the process even though eventually it
> succeed:
> # During table creation, when a user calls listTables and then calls
> tableExists for this table after the table descriptor is created but before
> item is inserted to meta table. He will find the listTables includes a table
> but tableExists return false for that same table, this behavior is confusing
> and should only acceptable during the table is being deleted...
> # Similar behavior occurs during table deletion.
> Seems the benefit of implementing tableExists this way is we can avoid
> talking with HMaster, considering we talk with HMaster for listTables and
> getTableDescriptor, such benefit can't offset the drawback from inconsistency.
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