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From Eugene Kirpichov <>
Subject Re: WriteTOBigQuery/BatchLoads/ReifyResults step taking hours
Date Mon, 05 Mar 2018 22:28:39 GMT
For now I suggest that you augment your AvroIO.parse() with
.withHintMatchesManyFiles() because it appears to match a very large number
of tiny files, and I think that's what's causing the issue.

By default Dataflow uses 1 shard per file, and that causes 2 problems here:
- Each of these shards writes a separate file to be loaded into BigQuery,
so BigQuery has to load this many (tiny) files, which is not great.
- What's worse, the ReifyResults step takes this list of written temporary
files as a side input, and given Dataflow's way of materializing side
inputs, it behaves pretty bad when the data for the side input is written
from a very large number of shards.

I'm not sure there's an easy fix to make your original code perform well
unchanged, but .withHintMatchesManyFiles() should make it perform orders of
magnitude better.

On Mon, Mar 5, 2018 at 2:19 PM Eugene Kirpichov <>

> Thank you - I was wrong, it is indeed not blocked by BigQuery jobs, but by
> something it shouldn't be doing at all. This is definitely a bug. I'll
> investigate in more detail and file a JIRA so you can track the resolution.
> On Mon, Mar 5, 2018 at 7:12 AM Andrew Jones <>
> wrote:
>> Thanks for the reply. In my case the time is spent *before* the load job
>> has started. See attached for a screenshot of a currently running job (id:
>> 2018-03-05_04_06_20-5803269526385225708).
>> It looks like the time is spent in the ReifyResults step. Looking at the
>> code and at some smaller, succeeding jobs, the BigQuery loads normally
>> happen in SinglePartitionWriteTables (and
>> presumably MultiPartitionsWriteTables, if required). So I'm not seeing any
>> log lines with output from the BigQuery API, nor anything on the BigQuery
>> side.
>> The input to ReifyResults is around ~200K elements,
>> from WriteBundlesToFiles. Looking at the code, I think these are all the
>> files staged and ready for loading. I'm finding it hard to work out exactly
>> what ReifyResults is supposed to be doing and why it would take any time at
>> all. I think it might be going through these 200K files and doing something
>> with them, which if it's doing it one at a time and if the calls to the GCS
>> API is expensive then it could be the issue?
>> On Mon, 5 Mar 2018, at 00:28, Eugene Kirpichov wrote:
>> BigQueryIO.write() works by: 1) having Dataflow workers write data to
>> files (in parallel) 2) asking BigQuery to load those files - naturally,
>> during this time Dataflow workers aren't doing anything, that's why the job
>> is scaling down.
>> These jobs are spending time waiting for BigQuery to load the data.
>> As for why it's taking so long for BigQuery to load the data: You can try
>> to look for BigQuery job ids in the Stackdriver logs, and then inspect
>> these jobs in the BigQuery UI. If it's taking *really* long, it's usually a
>> quota issue: i.e. your BigQuery jobs are waiting for some other BigQuery
>> jobs to complete before even starting.
>> On Sat, Mar 3, 2018 at 3:30 AM Andrew Jones <>
>> wrote:
>> Hi,
>> We have a Dataflow job that loads data from GCS, does a bit of
>> transformation, then writes to a number of BigQuery tables using
>> DynamicDestinations.
>> The same job runs on smaller data sets (~70 million records), but this
>> one is struggling when processing ~500 million records. Both jobs are
>> writing to the same amount of tables - the only difference is the amount of
>> records.
>> Example job IDs include 2018-03-02_04_29_44-2181786949469858712 and
>> 2018-03-02_08_46_28-4580218739500768796. They are using BigQuery.IO to
>> write to BigQuery, using the BigQueryIO.Write.Method.FILE_LOADS method (the
>> default for a bounded job). They successfully stage all their data to GCS,
>> but then for some reason scale down the amount of workers to 1 when
>> processing the step WriteTOBigQuery/BatchLoads/ReifyResults and stay in
>> that step for hours.
>> In the logs we see many entries like this:
>> Proposing dynamic split of work unit
>> ...-7e07;2018-03-02_04_29_44-2181786949469858712;662185752552586455 at
>> {"fractionConsumed":0.5}
>> Rejecting split request because custom reader returned null residual
>> source.
>> And also occasionally this:
>> Processing lull for PT24900.038S in state process of
>> WriteTOBigQuery/BatchLoads/ReifyResults/ParDo(Anonymous) at
>> Method) at
>> at
>> at
>> ...
>> The job does seem to eventually progress, but after many hours. It then
>> fails later with this error, which may or may not be related (just starting
>> to look in to):
>> (94794e1a2c96f380): java.lang.RuntimeException:
>> org.apache.beam.sdk.util.UserCodeException: Unable to
>> patch table description: {datasetId=..., projectId=...,
>> tableId=9c20908cc6e549b4a1e116af54bb8128_011249028ddcc5204885bff04ce2a725_00001_00000},
>> aborting after 9 retries.
>> We're not sure how to proceed, so any pointers would be appreciated.
>> Thanks,
>> Andrew

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