flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Stephan Ewen <se...@apache.org>
Subject Re: Parallel file read in LocalEnvironment
Date Wed, 18 Nov 2015 18:22:34 GMT
Okay, let me take a step back and make sure I understand this right...

With many small files it takes longer to start the job, correct? How much
time did it actually take and how many files did you have?


On Wed, Nov 18, 2015 at 7:18 PM, Flavio Pompermaier <pompermaier@okkam.it>
wrote:

> in my test I was using the local fs (ext4)
> On 18 Nov 2015 19:17, "Stephan Ewen" <sewen@apache.org> wrote:
>
>> The JobManager does not read all files, but is has to query the HDFS for
>> all file metadata (size, blocks, block locations), which can take a bit.
>> There is a separate call to the HDFS Namenode for each file. The more
>> files, the more metadata has to be collected.
>>
>>
>> On Wed, Nov 18, 2015 at 7:15 PM, Flavio Pompermaier <pompermaier@okkam.it
>> > wrote:
>>
>>> So why it takes so much to start the job?because in any case the job
>>> manager has to read all the lines of the input files before generating the
>>> splits?
>>> On 18 Nov 2015 17:52, "Stephan Ewen" <sewen@apache.org> wrote:
>>>
>>>> Late answer, sorry:
>>>>
>>>> The splits are created in the JobManager, so the sub submission should
>>>> not be affected by that.
>>>>
>>>> The assignment of splits to workers is very fast, so many splits with
>>>> small data is not very different from few splits with large data.
>>>>
>>>> Lines are never materialized and the operators do not work differently
>>>> based on different numbers of splits.
>>>>
>>>> On Wed, Oct 7, 2015 at 4:26 PM, Flavio Pompermaier <
>>>> pompermaier@okkam.it> wrote:
>>>>
>>>>> I've tried to split my huge file by lines count (using the bash
>>>>> command split -l) in 2 different ways:
>>>>>
>>>>>    1. small lines count (huge number of small files)
>>>>>    2. big lines count (small number of big files)
>>>>>
>>>>> I can't understand why the time required to effectively start the job
>>>>> is more or less the same
>>>>>
>>>>>    - in 1. it takes a lot to fetch the file list (~50.000) and the
>>>>>    split assigner is fast to assign the splits (but also being fast they
are a
>>>>>    lot)
>>>>>    - in 2. Flink is fast in fetch the file list but it's extremely
>>>>>    slow to generate the splits to assign
>>>>>
>>>>> Initially I was thinking that Flink was eagerly materializing the
>>>>> lines somewhere but both the memory and the disks doesn't increase.
>>>>> What is going on underneath? Is it normal?
>>>>>
>>>>> Thanks in advance,
>>>>> Flavio
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Oct 7, 2015 at 3:27 PM, Stephan Ewen <sewen@apache.org>
wrote:
>>>>>
>>>>>> The split functionality is in the FileInputFormat and the
>>>>>> functionality that takes care of lines across splits is in the
>>>>>> DelimitedIntputFormat.
>>>>>>
>>>>>> On Wed, Oct 7, 2015 at 3:24 PM, Fabian Hueske <fhueske@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> I'm sorry there is no such documentation.
>>>>>>> You need to look at the code :-(
>>>>>>>
>>>>>>> 2015-10-07 15:19 GMT+02:00 Flavio Pompermaier <pompermaier@okkam.it>
>>>>>>> :
>>>>>>>
>>>>>>>> And what is the split policy for the FileInputFormat?it depends
on
>>>>>>>> the fs block size?
>>>>>>>> Is there a pointer to the several flink input formats and
a
>>>>>>>> description of their internals?
>>>>>>>>
>>>>>>>> On Wed, Oct 7, 2015 at 3:09 PM, Fabian Hueske <fhueske@gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Hi Flavio,
>>>>>>>>>
>>>>>>>>> it is not possible to split by line count because that
would mean
>>>>>>>>> to read and parse the file just for splitting.
>>>>>>>>>
>>>>>>>>> Parallel processing of data sources depends on the input
splits
>>>>>>>>> created by the InputFormat. Local files can be split
just like files in
>>>>>>>>> HDFS. Usually, each file corresponds to at least one
split but multiple
>>>>>>>>> files could also be put into a single split if necessary.The
logic for that
>>>>>>>>> would go into to the InputFormat.createInputSplits()
method.
>>>>>>>>>
>>>>>>>>> Cheers, Fabian
>>>>>>>>>
>>>>>>>>> 2015-10-07 14:47 GMT+02:00 Flavio Pompermaier <
>>>>>>>>> pompermaier@okkam.it>:
>>>>>>>>>
>>>>>>>>>> Hi to all,
>>>>>>>>>>
>>>>>>>>>> is there a way to split a single local file by line
count (e.g. a
>>>>>>>>>> split every 100 lines) in a LocalEnvironment to speed
up a simple map
>>>>>>>>>> function? For me it is not very clear how the local
files (files into
>>>>>>>>>> directory if recursive=true) are managed by Flink..is
there any ref to this
>>>>>>>>>> internals?
>>>>>>>>>>
>>>>>>>>>> Best,
>>>>>>>>>> Flavio
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>

Mime
View raw message