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From William Shen <wills...@marinsoftware.com>
Subject Re: "upsert select" with "limit" clause
Date Tue, 18 Dec 2018 18:48:31 GMT
Shawn, in my own investigation with the SELECT statements running slower
with LIMIT, I have found that with the limit under certain threshold,
Phoenix will perform the scan in SERIAL instead of PARALLEL. Not sure why
that is the case, but maybe your explain plan would yield the same insight.

On Tue, Dec 18, 2018 at 10:30 AM Vincent Poon <vincentpoon@apache.org>
wrote:

> Shawn,
>
> Can you do an "explain" to show what your two statements are doing?  That
> might give some clues.  Perhaps one is able to be run on the server for
> some reason and the other is not.
> Otherwise, I don't see why one would be substantially slower than the
> other.
>
> Vincent
>
> On Mon, Dec 17, 2018 at 9:14 PM Shawn Li <shawnlijob@gmail.com> wrote:
>
>> Hi Jonathan,
>>
>> The single threaded on one side sounds logical to me. Hopefully Vincent
>> can confirm it.
>>
>> Thanks,
>> Shawn
>>
>> On Mon, Dec 17, 2018 at 9:25 PM Jonathan Leech <jonathaz@gmail.com>
>> wrote:
>>
>>> My guess is that in order to enforce the limit that it’s effectively
>>> single threaded in either the select or the upsert.
>>>
>>> On Dec 17, 2018, at 6:43 PM, Shawn Li <shawnlijob@gmail.com> wrote:
>>>
>>> Hi Vincent,
>>>
>>> Thanks for explaining. That makes much more sense now and it explains
>>> the high memory usage when without "limit" clause. Because it upserts much
>>> quickly when using "upsert select" without "limit", the memory usage in
>>> client machine is much higher than "upsert select" with "limit" .
>>>
>>> So back to the other question. Can you explain what is underlying
>>> Phoenix implementation for "upsert select limit"? Why it is slower than
>>> without "limit" when insert a huge number (2m rows) like ""upsert into
>>> table2 select * from table1 limit 2,000,000;". This is much slower than
>>> inserting the whole table (upsert into table2 select * from table1;).
>>>
>>> Thanks,
>>> Xiang
>>>
>>>
>>> On Mon, Dec 17, 2018 at 1:56 PM Vincent Poon <vincentpoon@apache.org>
>>> wrote:
>>>
>>>> Shawn,
>>>> Your query *upsert into table2 select * from table1;  *would not be
>>>> run on the server - the source and target table are different.  It would
>>>> have to be something like:
>>>> *upsert into table1 select * from table1;*
>>>>
>>>> If you want to run server-side upsert select on a target table that is
>>>> different from the source table, you need to set
>>>> "phoenix.client.enable.server.upsert.select" to true on your client.
>>>> The are some other restrictions: the table can't have any global
>>>> indexes, and the statement can't have a join or where subquery.  We need
to
>>>> update the documentation with this information.
>>>>
>>>> The reason there are all these hurdles is because it's generally not
>>>> recommended to do server-side upsert select across different tables,
>>>> because that means you're doing cross-regionserver RPCs (e.g. read data
>>>> from a region of sourcetable, and write to a region of targettable on a
>>>> different regionserver), potentially tying up handlers in an unpredictable
>>>> way.
>>>>
>>>> On Sun, Dec 16, 2018 at 7:12 PM Shawn Li <shawnlijob@gmail.com> wrote:
>>>>
>>>>> Hi Jaanai,
>>>>>
>>>>> According to Phoenix website, " If auto commit is on, and both a) the
>>>>> target table matches the source table, and b) the select performs no
>>>>> aggregation, then the population of the target table will be done
>>>>> completely on the server-side (with constraint violations logged, but
>>>>> otherwise ignored). Otherwise, data is buffered on the client and, if
auto
>>>>> commit is on, committed in row batches as specified by the UpsertBatchSize
>>>>> connection property (or the phoenix.mutate.upsertBatchSize HBase config
>>>>> property which defaults to 10000 rows)"
>>>>>
>>>>> And our sql statement is just: *upsert into table2 select * from
>>>>> table1; *which should match the first case, all operations should be
>>>>> in server site. But the memory usage on the client machine is higher
than
>>>>> "upsert select limit" clause. And the memory usage is check by run 'top'
>>>>> command under Linux. So we are sure it is caused by "select upsert" in
>>>>> Phoenix and not others, and can't explain why there is so high memory
usage
>>>>> on client/gateway machine when all operations are supposed to happen
on the
>>>>> serve side.
>>>>>
>>>>> Thanks,
>>>>> Shawn
>>>>>
>>>>> On Thu, Dec 13, 2018 at 3:15 AM Jaanai Zhang <cloud.poster@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Shawn,
>>>>>>
>>>>>> The UPSERT SELECT will run in a coprocessor on if it hasn't limit
>>>>>> clause, only query 1 table, the query is doing aggregation, no sequences
>>>>>> and auto commit is on. Please check your SQL ... and you can also
check
>>>>>> whether some resources have not been released.
>>>>>>
>>>>>> ----------------------------------------
>>>>>>    Jaanai Zhang
>>>>>>    Best regards!
>>>>>>
>>>>>>
>>>>>>
>>>>>> Shawn Li <shawnlijob@gmail.com> 于2018年12月13日周四
下午12:10写道:
>>>>>>
>>>>>>> Hi Jaanai,
>>>>>>>
>>>>>>> Thanks for putting your thought. The behavior you describe is
>>>>>>> correct on the Hbase region sever side. The memory usage for
blockcache and
>>>>>>> memstore will be high under such high throughput. But our phoenix
client is
>>>>>>> on a gateway machine (no hbase region server sitting on it or
any Hbase
>>>>>>> service on it), so not sure how to explain such high memory usage
for
>>>>>>> upsert select without "limit" clause. The high memory usage behavior
like
>>>>>>> all select results send to client machine, cached in client machine's
>>>>>>> memory, and then insert back to target table, which is not like
the
>>>>>>> behavior that should happen, all of this should be done on the
server side
>>>>>>> as the table schema is exactly the same. By the way, this happens
on both
>>>>>>> Phoenix 4.7 and Phoenix 4.14.
>>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Shawn
>>>>>>>
>>>>>>> On Wed, Dec 12, 2018 at 10:26 PM Jaanai Zhang <
>>>>>>> cloud.poster@gmail.com> wrote:
>>>>>>>
>>>>>>>> Shawn,
>>>>>>>>
>>>>>>>>
>>>>>>>> For the upsert without limit,  which will read the source
table and
>>>>>>>> write the target tables on the server side.  I think the
higher memory
>>>>>>>> usage is caused by using scan cache and memstore under the
higher
>>>>>>>> throughput.
>>>>>>>>
>>>>>>>> ----------------------------------------
>>>>>>>>    Jaanai Zhang
>>>>>>>>    Best regards!
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Shawn Li <shawnlijob@gmail.com> 于2018年12月13日周四
上午10:13写道:
>>>>>>>>
>>>>>>>>> Hi Vincent,
>>>>>>>>>
>>>>>>>>> So you describe limit will sent result to client side
and then
>>>>>>>>> write to server, this might explain why upsert with limit
is slower than
>>>>>>>>> without limit. But looks like it can't explain the memory
usage? The memory
>>>>>>>>> usage on client machine is 8gb (without "limit") vs 2gb
(with limit),
>>>>>>>>> sometime upsert without "limit" can even reach 20gb for
big table.
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Shawn
>>>>>>>>>
>>>>>>>>> On Wed, Dec 12, 2018 at 6:34 PM Vincent Poon <
>>>>>>>>> vincentpoon@apache.org> wrote:
>>>>>>>>>
>>>>>>>>>> I think it's done client-side if you have LIMIT.
 If you have
>>>>>>>>>> e.g. LIMIT 1000 , it would be incorrect for each
regionserver to upsert
>>>>>>>>>> 100, if you have more than one regionserver.  So
instead results are sent
>>>>>>>>>> back to the client, where the LIMIT is applied and
then written back to the
>>>>>>>>>> server in the UPSERT.
>>>>>>>>>>
>>>>>>>>>> On Wed, Dec 12, 2018 at 1:18 PM Shawn Li <shawnlijob@gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> Hi Vincent,
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> The table creation statement is similar to below.
We have about
>>>>>>>>>>> 200 fields. Table is mutable and don’t have
any index on the table.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> CREATE TABLE IF NOT EXISTS us_population (
>>>>>>>>>>>
>>>>>>>>>>>       state CHAR(2) NOT NULL,
>>>>>>>>>>>
>>>>>>>>>>>       city VARCHAR,
>>>>>>>>>>>
>>>>>>>>>>>       population BIGINT,
>>>>>>>>>>>
>>>>>>>>>>>       …
>>>>>>>>>>>
>>>>>>>>>>>       CONSTRAINT my_pk PRIMARY KEY (state));
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>>
>>>>>>>>>>> Shawn
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Dec 12, 2018, 13:42 Vincent Poon <vincentpoon@apache.org
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> For #2, can you provide the table definition
and the statement
>>>>>>>>>>>> used?  e.g. Is the table immutable, or does
it have indexes?
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Dec 11, 2018 at 6:08 PM Shawn/Xiang
Li <
>>>>>>>>>>>> shawnlijob@gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Hi,
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> 1.       Want to check what is underlying
running for limit
>>>>>>>>>>>>> clause used in the following Upsert statement
(is it involving any
>>>>>>>>>>>>> coprocessor working behind?):
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> *                                  upsert
into table2 select *
>>>>>>>>>>>>> from table1 limit 3000000; * (table 1
and table 2 have same
>>>>>>>>>>>>> schema)
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>               The above statement is
running a lot slower than
>>>>>>>>>>>>> without “limit”  clause as shown
in following, even the above statement
>>>>>>>>>>>>> upsert less data:
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> *                                upsert
into table2 select *
>>>>>>>>>>>>> from table1;*
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> 2.       We also observe memory usable
is pretty high without
>>>>>>>>>>>>> the limit clause (8gb vs 2gb), sometimes
for big table it can reach 20gb
>>>>>>>>>>>>> without using limit clause.  According
to phoenix website description for
>>>>>>>>>>>>> upsert select “If auto commit is on,
and both a) the target table matches
>>>>>>>>>>>>> the source table, and b) the select performs
no aggregation, then the
>>>>>>>>>>>>> population of the target table will be
done completely on the server-side
>>>>>>>>>>>>> (with constraint violations logged, but
otherwise ignored).”
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>                My question is If everything
is done on
>>>>>>>>>>>>> server-side, how come we have such high
memory usage on the client machine?
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>
>>>>>>>>>>>>> Shawn
>>>>>>>>>>>>>
>>>>>>>>>>>>

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