[ 
https://issues.apache.org/jira/browse/PHOENIX-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16540261#comment-16540261
 ] 

ASF GitHub Bot commented on PHOENIX-3534:
-----------------------------------------

Github user twdsilva commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/303#discussion_r201741221
  
    --- Diff: 
phoenix-core/src/main/java/org/apache/phoenix/coprocessor/MetaDataEndpointImpl.java
 ---
    @@ -2147,46 +2566,29 @@ private MetaDataMutationResult doDropTable(byte[] 
key, byte[] tenantId, byte[] s
                 }
     
                 if (tableType == PTableType.TABLE || tableType == 
PTableType.SYSTEM) {
    -                // Handle any child views that exist
    -                TableViewFinder tableViewFinderResult = 
findChildViews(region, tenantId, table, clientVersion, !isCascade);
    -                if (tableViewFinderResult.hasViews()) {
    -                    if (isCascade) {
    -                        if 
(tableViewFinderResult.allViewsInMultipleRegions()) {
    -                            // We don't yet support deleting a table with 
views where SYSTEM.CATALOG has split and the
    -                            // view metadata spans multiple regions
    -                            return new 
MetaDataMutationResult(MutationCode.UNALLOWED_TABLE_MUTATION,
    -                                    
EnvironmentEdgeManager.currentTimeMillis(), null);
    -                        } else if 
(tableViewFinderResult.allViewsInSingleRegion()) {
    -                            // Recursively delete views - safe as all the 
views as all in the same region
    -                            for (ViewInfo viewInfo : 
tableViewFinderResult.getViewInfoList()) {
    -                                byte[] viewTenantId = 
viewInfo.getTenantId();
    -                                byte[] viewSchemaName = 
viewInfo.getSchemaName();
    -                                byte[] viewName = viewInfo.getViewName();
    -                                byte[] viewKey = 
SchemaUtil.getTableKey(viewTenantId, viewSchemaName, viewName);
    -                                Delete delete = new Delete(viewKey, 
clientTimeStamp);
    -                                rowsToDelete.add(delete);
    -                                acquireLock(region, viewKey, locks);
    -                                MetaDataMutationResult result = 
doDropTable(viewKey, viewTenantId, viewSchemaName,
    -                                        viewName, null, PTableType.VIEW, 
rowsToDelete, invalidateList, locks,
    -                                        tableNamesToDelete, 
sharedTablesToDelete, false, clientVersion);
    -                                if (result.getMutationCode() != 
MutationCode.TABLE_ALREADY_EXISTS) { return result; }
    -                            }
    -                        }
    -                    } else {
    +                // check to see if the table has any child views
    +                try (Table hTable =
    +                        env.getTable(SchemaUtil.getPhysicalTableName(
    +                            
PhoenixDatabaseMetaData.SYSTEM_CHILD_LINK_NAME_BYTES,
    +                            env.getConfiguration()))) {
    +                    boolean hasChildViews =
    +                            ViewFinder.hasChildViews(hTable, tenantId, 
schemaName, tableName,
    +                                clientTimeStamp);
    +                    if (hasChildViews && !isCascade) {
    --- End diff --
    
    I think we can handle the race condition in a similar way to how we handle 
conflicting columns using checkAndMutate. I have updated PHOENIX-4799 to 
include this case.


> Support multi region SYSTEM.CATALOG table
> -----------------------------------------
>
>                 Key: PHOENIX-3534
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-3534
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: James Taylor
>            Assignee: Thomas D'Silva
>            Priority: Major
>             Fix For: 5.0.0, 4.15.0
>
>         Attachments: PHOENIX-3534.patch
>
>
> Currently Phoenix requires that the SYSTEM.CATALOG table is single region 
> based on the server-side row locks being held for operations that impact a 
> table and all of it's views. For example, adding/removing a column from a 
> base table pushes this change to all views.
> As an alternative to making the SYSTEM.CATALOG transactional (PHOENIX-2431), 
> when a new table is created we can do a lazy cleanup  of any rows that may be 
> left over from a failed DDL call (kudos to [~lhofhansl] for coming up with 
> this idea). To implement this efficiently, we'd need to also do PHOENIX-2051 
> so that we can efficiently find derived views.
> The implementation would rely on an optimistic concurrency model based on 
> checking our sequence numbers for each table/view before/after updating. Each 
> table/view row would be individually locked for their change (metadata for a 
> view or table cannot span regions due to our split policy), with the sequence 
> number being incremented under lock and then returned to the client.



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