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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-2722) support mysql "limit,offset" clauses
Date Wed, 06 Apr 2016 07:24:25 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-2722?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15227883#comment-15227883
] 

ASF GitHub Bot commented on PHOENIX-2722:
-----------------------------------------

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

    https://github.com/apache/phoenix/pull/154#discussion_r58661601
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/iterate/OffsetScanGrouper.java
---
    @@ -0,0 +1,44 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + * http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.phoenix.iterate;
    +
    +import java.util.List;
    +
    +import org.apache.hadoop.hbase.client.Scan;
    +import org.apache.phoenix.compile.QueryPlan;
    +
    +/**
    + * Default implementation that creates a scan group if a plan is row key ordered (which
requires a merge sort),
    + * or if a scan crosses a region boundary and the table is salted or a local index. 
 
    + */
    +public class OffsetScanGrouper implements ParallelScanGrouper {
    --- End diff --
    
    Scans aren't done in parallel for SerialIterator, they're done serially. Have you tried
it without this? I can't figure out what purpose it's serving, but perhaps I'm missing something?


> support mysql "limit,offset" clauses 
> -------------------------------------
>
>                 Key: PHOENIX-2722
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2722
>             Project: Phoenix
>          Issue Type: New Feature
>            Reporter: Ankit Singhal
>            Assignee: Ankit Singhal
>            Priority: Minor
>         Attachments: PHOENIX-2722.patch, PHOENIX-2722_formatted.patch
>
>
> For serial query(query with “serial" hint or  “limit" without "order by”), we can
limit each scan(using page filter) to “limit+offset” instead of limit earlier.
> And then, for all queries, we can forward the relevant client iterators to the offset
provided and then return the result.
> syntax
> {code}
> [ LIMIT { count } ]
>     [ OFFSET start [ ROW | ROWS ] ]
>     [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]
> {code}
> Some new keywords(OFFSET,FETCH,ROW, ROWS,ONLY) are getting introduced so users might
need to see that they are not using them as column name or something.
> WDYT, [~jamestaylor]



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