Thanks Emilio. I left some more comments on the PR. I'm going to make
a pass through the C++ implementation and add some paranoia checks on
both the write path and the read path. I'll push these changes to your
PR branch so we have things integration tested together.

On the write path, per ARROW-1224 I think we can relax buffer padding
to 8 byte multiples rather than 64 bytes. I will also make sure the
schema message is being properly padded.

On the read path, I'll add some debug assertions that all buffers
start on aligned offsets, and that message bodies are always a
multiple of 8. This will help enforce these contracts with other Arrow
implementations when integration testing.

- Wes

On Tue, Aug 8, 2017 at 2:11 PM, Emilio Lahr-Vivaz <elahrvi...@ccri.com> wrote:
> I opened a PR for comments here: https://github.com/apache/arrow/pull/954
>
> So far I've just added some padding to the end of the buffers. I probably
> will need to pad the schema out as well... I'm testing things out against
> the js code at the moment.
>
>
> On 08/08/2017 02:06 PM, Wes McKinney wrote:
>>
>> I opened https://issues.apache.org/jira/browse/ARROW-1343. Let's try
>> to resolve this today so it can make the 0.6.0 release?
>>
>> On Tue, Aug 8, 2017 at 2:03 PM, Wes McKinney <wesmck...@gmail.com> wrote:
>>>
>>> I'm happy to have a look at the branch / integration tests if you
>>> could put up a PR
>>>
>>> When you say "a single serialized record batch" you mean an
>>> encapsulated message, right (including length prefix and metadata)?
>>> Using the terminology from http://arrow.apache.org/docs/ipc.html. I
>>> guess the problem is that the total size of the Schema message at the
>>> start of the stream may not be a multiple of 8. We should totally fix
>>> this; I don't think it even constitutes a breakage of the format -- I
>>> am fairly sure with extra padding bytes between the schema and the
>>> first record batch (or first dictionary) that the stream will be
>>> backwards compatible.
>>>
>>> However, we should document in
>>> https://github.com/apache/arrow/blob/master/format/IPC.md that message
>>> sizes are expected to be a multiple of 8. We should also take a look
>>> at the File format implementation to ensure that padding is inserted
>>> after the magic number at the start of the file
>>>
>>> - Wes
>>>
>>> On Tue, Aug 8, 2017 at 1:32 PM, Emilio Lahr-Vivaz <elahrvi...@ccri.com>
>>> wrote:
>>>>
>>>> Sure, the workflow is a little complicated, but we have the following
>>>> code
>>>> running in distributed databases (as accumulo iterators and hbase
>>>> coprocessors). They process data rows and transform them into arrow
>>>> records,
>>>> then periodically write out record batches:
>>>>
>>>>
>>>> https://github.com/locationtech/geomesa/blob/master/geomesa-index-api/src/main/scala/org/locationtech/geomesa/index/iterators/ArrowBatchScan.scala#L79-L105
>>>>
>>>>
>>>> https://github.com/locationtech/geomesa/blob/master/geomesa-arrow/geomesa-arrow-gt/src/main/scala/org/locationtech/geomesa/arrow/io/records/RecordBatchUnloader.scala#L20
>>>>
>>>> The record batches come back to a single client and are concatenated
>>>> with a
>>>> file header and footer (then wrapped in SimpleFeature objects, as we
>>>> implement a geotools data store):
>>>>
>>>>
>>>> https://github.com/locationtech/geomesa/blob/master/geomesa-index-api/src/main/scala/org/locationtech/geomesa/index/iterators/ArrowBatchScan.scala#L265-L268
>>>>
>>>> The resulting bytes are written out as an arrow streaming file that we
>>>> parse
>>>> with the arrow-js libraries in the browser.
>>>>
>>>> Thanks,
>>>>
>>>> Emilio
>>>>
>>>>
>>>> On 08/08/2017 01:24 PM, Li Jin wrote:
>>>>>
>>>>> Hi Emilio,
>>>>>
>>>>>> So I think the issue is that we are serializing record batches in a
>>>>>
>>>>> distributed fashion, and then > concatenating them in the streaming
>>>>> format.
>>>>>
>>>>> Can you show the code for this?
>>>>>
>>>>> On Tue, Aug 8, 2017 at 12:35 PM, Emilio Lahr-Vivaz
>>>>> <elahrvi...@ccri.com>
>>>>> wrote:
>>>>>
>>>>>> So I think the issue is that we are serializing record batches in a
>>>>>> distributed fashion, and then concatenating them in the streaming
>>>>>> format.
>>>>>> However, the message serialization only aligns the start of the
>>>>>> buffers,
>>>>>> which requires it to know the current absolute offset of the output
>>>>>> stream.
>>>>>> Would there be any problem with padding the end of the message, so any
>>>>>> single serialized record batch would always be a multiple of 8 bytes?
>>>>>>
>>>>>> I've put together a branch that does this, and the existing java tests
>>>>>> all
>>>>>> pass. I'm having some trouble running the integration tests though.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Emilio
>>>>>>
>>>>>>
>>>>>> On 08/08/2017 09:18 AM, Emilio Lahr-Vivaz wrote:
>>>>>>
>>>>>>> Hi Wes,
>>>>>>>
>>>>>>> You're right, I just realized that. I think the alignment issue might
>>>>>>> be
>>>>>>> in some unrelated code, actually. From what I can tell the the arrow
>>>>>>> writers are aligning buffers correctly; if not I'll open a bug.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Emilio
>>>>>>>
>>>>>>> On 08/08/2017 09:15 AM, Wes McKinney wrote:
>>>>>>>
>>>>>>>> hi Emilio,
>>>>>>>>
>>>>>>>>    From your description, it isn't clear why 8-byte alignment is
>>>>>>>> causing
>>>>>>>> a problem (as compare with 64-byte alignment). My understanding is
>>>>>>>> that JavaScript's TypedArray classes range in size from 1 to 8
>>>>>>>> bytes.
>>>>>>>>
>>>>>>>> The starting offset for all buffers should be 8-byte aligned, if not
>>>>>>>> that is a bug. Could you clarify?
>>>>>>>>
>>>>>>>> - Wes
>>>>>>>>
>>>>>>>> On Tue, Aug 8, 2017 at 8:52 AM, Emilio Lahr-Vivaz
>>>>>>>> <elahrvi...@ccri.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> After looking at it further, I think only the buffers themselves
>>>>>>>>> need
>>>>>>>>> to be
>>>>>>>>> aligned, not the metadata and/or schema. Would there be any problem
>>>>>>>>> with
>>>>>>>>> changing the alignment to 64 bytes then?
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Emilio
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 08/08/2017 08:08 AM, Emilio Lahr-Vivaz wrote:
>>>>>>>>>
>>>>>>>>>> I'm looking into buffer alignment in the java writer classes.
>>>>>>>>>> Currently
>>>>>>>>>> some files written with the java streaming writer can't be read
>>>>>>>>>> due
>>>>>>>>>> to
>>>>>>>>>> the
>>>>>>>>>> javascript TypedArray's restriction that the start offset of the
>>>>>>>>>> array
>>>>>>>>>> must
>>>>>>>>>> be a multiple of the data size of the array type (i.e.
>>>>>>>>>> Int32Vectors
>>>>>>>>>> must
>>>>>>>>>> start on a multiple of 4, Float64Vectors must start on a multiple
>>>>>>>>>> of
>>>>>>>>>> 8,
>>>>>>>>>> etc). From a cursory look at the java writer, I believe that the
>>>>>>>>>> schema that
>>>>>>>>>> is written first is not aligned at all, and then each record batch
>>>>>>>>>> pads out
>>>>>>>>>> its size to a multiple of 8. So:
>>>>>>>>>>
>>>>>>>>>> 1. should the schema block pad itself so that the first record
>>>>>>>>>> batch
>>>>>>>>>> is
>>>>>>>>>> aligned, and is there any problem with doing so?
>>>>>>>>>> 2. is there any problem with changing the alignment to 64 bytes,
>>>>>>>>>> as
>>>>>>>>>> recommended (but not required) by the spec?
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>>
>>>>>>>>>> Emilio
>>>>>>>>>>
>

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