So if either or both sides of a sort-merge-join will have to be sorted simply depends on whether this side is already ordered on the join key.

So far we don't have any documentation specifically for explain plan yet, but the Phoenix website does have some examples for different types of queries or functionalities, including join queries.


Thanks,
Maryann

On Wed, Sep 28, 2016 at 10:52 PM, Sumit Nigam <sumit_only@yahoo.com> wrote:
Thanks Maryann.

Yes let me switch to merge sort join because the other query uses lots more columns. Also, if I just change the hint to use merge sort would that be enough or I need to sort both the driving query and subquery with same order by for merge sort?

As an aside, is there a document to interpret explain plan?

Thanks,
Sumit


From: Maryann Xue <maryann.xue@gmail.com>
To: Sumit Nigam <sumit_only@yahoo.com>
Cc: "user@phoenix.apache.org" <user@phoenix.apache.org>
Sent: Thursday, September 29, 2016 11:03 AM
Subject: Re: Hash join confusion

Thank you Sumit, for trying this out! So right now it's very clear that the table to be cached IS too big so there should be no point of using hash join in this case. Is the other table much smaller, or it is about the same size or even bigger? If it's considerably smaller you can probably rewrite your query to do the join the other way, otherwise let's just stick to sort-merge join.


Thanks,
Maryann

On Wed, Sep 28, 2016 at 10:29 PM, Sumit Nigam <sumit_only@yahoo.com> wrote:
Thank you Maryann.

I am not using multi-tenancy for these tables. Increasing phoenix. coprocessor.maxServerCacheTime ToLiveMs and the corresponding cache size config just delayed the error. 

I have also started seeing some memory problem -

Caused by: org.apache.phoenix.memory.Insu fficientMemoryException: Requested memory of 22871932 bytes could not be allocated from remaining memory of 776776654 bytes from global pool of 778469376 bytes after waiting for 10000ms.
	at org.apache.phoenix.memory. GlobalMemoryManager. allocateBytes( GlobalMemoryManager.java:78)
	at org.apache.phoenix.memory. GlobalMemoryManager.access$ 300(GlobalMemoryManager.java: 30)
	at org.apache.phoenix.memory. GlobalMemoryManager$ GlobalMemoryChunk.resize( GlobalMemoryManager.java:139)

What I am having trouble with is, that the total size of csv produced by sub-query is only ~7Mb. I have 12 region servers with 5GB heap each. So, when this result gets sent across to all region servers to perform the server side join, not sure why a memory issue should show up (or a time out occur). Any insights?

These tables are salted. Not sure if it is https://issues.apache.org/ jira/browse/PHOENIX-2900  issue. 

Switching to sort merge join helped. But not sure if that is the right solution going forward.

Thanks again!
Sumit



From: Maryann Xue <maryann.xue@gmail.com>
To: "user@phoenix.apache.org" <user@phoenix.apache.org>; Sumit Nigam <sumit_only@yahoo.com>
Sent: Wednesday, September 28, 2016 11:36 PM
Subject: Re: Hash join confusion

Yes, Sumit, the sub-query will get cached in hash join. Are you using multi-tenancy for these tables? If yes, you might want to checkout Phoenix 4.7 or 4.8, since a related bug fix got in the 4.7 release. https://issues. apache.org/jira/browse/ PHOENIX-2381?jql=project%20% 3D%20PHOENIX%20AND%20text%20~% 20%22hash%20cache%20id%22

Otherwise I think it's the hash cache timeout issue, in which case changing phoenix.coprocessor.m axServerCacheTimeToLiveMs migh t be helpful.


Thanks,
Maryann

On Tue, Sep 27, 2016 at 10:02 PM, Sumit Nigam <sumit_only@yahoo.com> wrote:
Hi,

Is there any document which can help me understand explain plan output in detail? Or, which piece of code should I look at, to get an idea?

Here is explain plan for inner join query below. Can anyone help in explaining it to me? Like, as per the plan which table is being cached, etc.?
Here, indx_exdocb is index table (on ID) and exDocStoreb is main table with rowkey as (current_timestamp, ID).

+----------------------------- -------------+
|                   PLAN                   |
+----------------------------- -------------+
| CLIENT 36-CHUNK PARALLEL 36-WAY FULL SCAN OVER exDocStoreb |
|     PARALLEL INNER-JOIN TABLE 0 (SKIP MERGE) |
|         CLIENT 36-CHUNK PARALLEL 36-WAY RANGE SCAN OVER indx_exdocb [0,' 42ecf4abd4bd7e7606025dc8eee3de 6a3cc04418cbc2619ddc01f54d88d7 c3bf'] - [0,' 42ecf4abd4bd7e7606025dc8eee3de 6a3cc04418cbc2619ddc01f54d88d7 c3bg' |
|             SERVER FILTER BY FIRST KEY ONLY |
|             SERVER AGGREGATE INTO ORDERED DISTINCT ROWS BY ["ID"] |
|         CLIENT MERGE SORT                |
|     DYNAMIC SERVER FILTER BY (A.CURRENT_TIMESTAMP, A.ID) IN ((TMP.MCT, TMP.TID)) |
+----------------------------- -------------+

Also, is there a way to turn ON more verbose explain plan? Like, seeing number of bytes, rows that each step results in?

Thanks,
Sumit


From: Sumit Nigam <sumit_only@yahoo.com>
To: Users Mail List Phoenix <user@phoenix.apache.org>
Sent: Tuesday, September 27, 2016 9:17 PM
Subject: Hash join confusion

Hi,

I am using hbase 1.1 with phoenix 4.6. 

I have a table with row key as (current_timestamp, id) which is salted and index on (id). This table has ~3 million records.

I have a query like given below. 

SELECT  ID, CURRENT_TIMESTAMP, <SOME OTHER COLUMNS> from TBL 
                       as a inner join (
                                select max(CURRENT_TIMESTAMP) as mct, ID as tid from TBL where ID like ' 42ecf4abd4bd7e7606025dc8eee3de 6a3cc04418cbc2619ddc01f54d88d7 c3bf%' group by ID) as tmp 
                       on a.ID=tmp.tid and a.CURRENT_TIMESTAMP=tmp.mct


The query hangs for long and finally fails with a timeout. I have 12 region servers each with 5GB heap and also the total records satisfying the above query is 62K whose CSV dump is ~10MB only. 

DoNotRetryIOException: Could not find hash cache for join Id: Ӧ8D. The cache might have expired and have been removed

and - 

Caused by: java.sql.SQLException: Encountered exception in sub plan [0] execution.
	at org.apache.phoenix.execute. HashJoinPlan.iterator( HashJoinPlan.java:175)
	at com.infa.products.ldm. ingestion.server.java.hadoop. impl. FixPhoenixIngestInputFormat. getQueryPlan( FixPhoenixIngestInputFormat. java:94)
	... 22 more

and
Caused by: java.sql.SQLException:
    java.util.concurrent.Timeo utException
        at org.apache.phoenix.cache. ServerCacheClient. addServerCache( ServerCacheClient.java:264)

I can try playing around with parameters such as phoenix.coprocessor. maxServerCacheTimeToLiveMs and switching to sort_merge_join actually helped.

But my question is as per Joins | Apache Phoenix in a case such as lhs INNER JOIN rhs, it is rhs which will be built as hash table in server cache. So, in the above query I assume this gets cached?

 select max(CURRENT_TIMESTAMP) as mct, ID as tid from TBL where ID like ' 42ecf4abd4bd7e7606025dc8eee3de 6a3cc04418cbc2619ddc01f54d88d7 c3bf%' group by ID) as tmp 

Thanks,
Sumit