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https://issues.apache.org/jira/browse/HBASE-10584?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Feng Honghua updated HBASE-10584:
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Issue Type: Sub-task (was: Bug)
Parent: HBASE-10628
> Inconsistency between tableExists and listTables in implementation
> ------------------------------------------------------------------
>
> Key: HBASE-10584
> URL: https://issues.apache.org/jira/browse/HBASE-10584
> Project: HBase
> Issue Type: Sub-task
> 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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