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From Alexey Serbin <aser...@cloudera.com>
Subject Re: strange behavior of getPendingErrors
Date Sat, 17 Nov 2018 15:13:07 GMT
Hey Todd,

Yes, that behavior is a bit strange especially given the fact that the
behavior differs when it comes to duplicate rows and other errors that
happen at later stages of 'applying' write operations at the server side.

I'll open a JIRA item about this issue.  If anyone disagrees, we can
resolve the JIRA item as needed.


Thanks,

Alexey

On Sat, Nov 17, 2018 at 12:01 AM Todd Lipcon <todd@cloudera.com> wrote:

> Hey Alexey,
>
> I think your explanation makes sense from an implementation perspective.
> But, I think we should treat this behavior as a bug. From the user
> perspective, such an error is a per-row data issue and should only affect
> the row with the problem, not some arbitrary subset of rows in the batch
> which happened to share a partition.
>
> Does anyone disagree?
>
> Todd
>
> On Fri, Nov 16, 2018, 9:28 PM Alexey Serbin <aserbin@cloudera.com wrote:
>
>> Hi Boris,
>>
>> Kudu clients (both Java and C++ ones) send write operations to
>> corresponding tablet servers in batches when using the AUTO_FLUSH_BACKGROUND
>> and MANUAL_FLUSH modes.  When a tablet server receives a Write RPC
>> (WriteRequestPB is the corresponding type of the parameter), it decodes the
>> operations from the batch:
>> https://github.com/apache/kudu/blob/master/src/kudu/tablet/local_tablet_writer.h#L97
>>
>> While decoding operations from a batch, various constraints are being
>> checked.  One of those is checking for nulls in non-nullable columns.  If
>> there is a row in the batch that violates the non-nullable constraint, the
>> whole batch is rejected.
>>
>> That's exactly what happened in your example: a batch to one tablet
>> consisted of 3 rows one of which had a row with violation of the
>> non-nullable constraint for the dt_tm column, so the whole batch of 3
>> operations was rejected.  You can play with different partition schemes:
>> e.g., in case of 10 hashed partitions it might happen that only 2
>> operations would be rejected, in case of 30 partitions -- just the single
>> key==2 row could be rejected.
>>
>> BTW, that might also happen if using the MANUAL_FLUSH mode.  However,
>> with the AUTO_FLUSH_SYNC mode, the client sends operations in batches of
>> size 1.
>>
>>
>> Kind regards,
>>
>> Alexey
>>
>> On Fri, Nov 16, 2018 at 7:24 PM Boris Tyukin <boris@boristyukin.com>
>> wrote:
>>
>>> Hi Todd,
>>>
>>> We are on Kudu 1.5 still and I used Kudu client 1.7
>>>
>>> Thanks,
>>> Boris
>>>
>>> On Fri, Nov 16, 2018, 17:07 Todd Lipcon <todd@cloudera.com wrote:
>>>
>>>> Hi Boris,
>>>>
>>>> This is interesting. Just so we're looking at the same code, what
>>>> version of the kudu-client dependency have you specified, and what version
>>>> of the server?
>>>>
>>>> -Todd
>>>>
>>>> On Fri, Nov 16, 2018 at 1:12 PM Boris Tyukin <boris@boristyukin.com>
>>>> wrote:
>>>>
>>>>> Hey guys,
>>>>>
>>>>> I am playing with Kudu Java client (wow it is fast), using mostly code
>>>>> from Kudu Java example.
>>>>>
>>>>> While learning about exceptions during rows inserts, I stumbled upon
>>>>> something I could not explain.
>>>>>
>>>>> If I insert 10 rows into a brand new Kudu table (AUTO_FLUSH_BACKGROUND
>>>>> mode) and I make one row to be "bad" intentionally (one column cannot
be
>>>>> NULL), I actually get 3 rows that cannot be inserted into Kudu, not 1
as I
>>>>> was expected.
>>>>>
>>>>> But if I do session.flush() after every single insert, I get only one
>>>>> error row (but this ruins the purpose of AUTO_FLUSH_BACKGROUND mode).
>>>>>
>>>>> Any ideas one? We cannot afford losing data and need to track all rows
>>>>> which cannot be inserted.
>>>>>
>>>>> AUTO_FLUSH mode works much better and I do not have an issue like
>>>>> above, but then it is way slower than AUTO_FLUSH_BACKGROUND.
>>>>>
>>>>> My code is below. It is in Groovy, but I think you will get an idea :)
>>>>> https://gist.github.com/boristyukin/8703d2c6ec55d6787843aa133920bf01
>>>>>
>>>>> Here is output from my test code that hopefully illustrates my
>>>>> confusion - out of 10 rows inserted, 9 should be good and 1 bad, but
it
>>>>> turns out Kudu flagged 3 as bad:
>>>>>
>>>>> Created table kudu_groovy_example
>>>>> Inserting 10 rows in AUTO_FLUSH_BACKGROUND flush mode ...
>>>>> (int32 key=1, string value="value 1", unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.469000Z)
>>>>> (int32 key=2, string value=NULL)  BAD ROW
>>>>> (int32 key=3, string value="value 3", unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.595000Z)
>>>>> (int32 key=4, string value=NULL, unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.596000Z)
>>>>> (int32 key=5, string value="value 5", unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.597000Z)
>>>>> (int32 key=6, string value=NULL, unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.597000Z)
>>>>> (int32 key=7, string value="value 7", unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.598000Z)
>>>>> (int32 key=8, string value=NULL, unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.602000Z)
>>>>> (int32 key=9, string value="value 9", unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.603000Z)
>>>>> (int32 key=10, string value=NULL, unixtime_micros
>>>>> dt_tm=2018-11-16T20:57:03.603000Z)
>>>>> 3 errors inserting rows - why 3???? only 1 expected to be bad...
>>>>> there were errors inserting rows to Kudu
>>>>> the first few errors follow:
>>>>> ??? key 1 and 6 supposed to be fine!
>>>>> Row error for primary key=[-128, 0, 0, 1], tablet=null, server=null,
>>>>> status=Invalid argument: No value provided for required column:
>>>>> dt_tm[unixtime_micros NOT NULL] (error 0)
>>>>> Row error for primary key=[-128, 0, 0, 2], tablet=null, server=null,
>>>>> status=Invalid argument: No value provided for required column:
>>>>> dt_tm[unixtime_micros NOT NULL] (error 0)
>>>>> Row error for primary key=[-128, 0, 0, 6], tablet=null, server=null,
>>>>> status=Invalid argument: No value provided for required column:
>>>>> dt_tm[unixtime_micros NOT NULL] (error 0)
>>>>> Rows counted in 485 ms
>>>>> Table has 7 rows - ??? supposed to be 9!
>>>>> INT32 key=4, STRING value=NULL, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.596000Z
>>>>> INT32 key=8, STRING value=NULL, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.602000Z
>>>>> INT32 key=9, STRING value=value 9, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.603000Z
>>>>> INT32 key=3, STRING value=value 3, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.595000Z
>>>>> INT32 key=10, STRING value=NULL, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.603000Z
>>>>> INT32 key=5, STRING value=value 5, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.597000Z
>>>>> INT32 key=7, STRING value=value 7, UNIXTIME_MICROS
>>>>> dt_tm=2018-11-16T20:57:03.598000Z
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> Todd Lipcon
>>>> Software Engineer, Cloudera
>>>>
>>>

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