Re: clashing hbase queries

[Pat Ferrel]

Status: clashing HBase queries was indeed the problem. I went back to an older 
version of the template, which did not cause the 2 tasks to be in parallel and 
things work fine. It only makes sense but the DAG is a mysterious thing so we 
need a way to serialize HBase access to stop it from being created in a 
pathological manner.


On Oct 15, 2016, at 3:14 PM, Pat Ferrel <p...@occamsmachete.com> wrote:

I may have been on the wrong track with the 2 parallel task idea, which is a 
problem. The typical use with Spark is to get all data out of HBase and work on 
it as RDDs but getting it out may cause parallel tasks to access HBase at the 
same time. There must be a way to serialize the execution of this kind of 
task—I just haven’t run into it, Maybe access the count of RDD items 
immediately to force the HBase queries to happen right away. But...

Looking a little deeper, below is a query that should return nothing, since 
there are no “item” objects. This seems like it is causing a full DB scan, 
which I suspect makes it a PIO bug, not an HBase thing. It is also easy to test 
and work around once I have access to the big fat cluster that it was happening 
on.

On Oct 13, 2016, at 6:52 PM, Andrew Purtell <andrew.purt...@gmail.com> wrote:

This sounds like hotspotting. Ideally the workload over the keyspace can be 
better distributed, which is another avenue of attack - partitioning, keying 
strategy.  


> On Oct 13, 2016, at 6:10 PM, Pat Ferrel <p...@occamsmachete.com> wrote:
> 
> The DAG for a template just happens to schedule 2 tasks that do something 
> like this:
> 
> val fieldsRDD: RDD[(ItemID, PropertyMap)] = PEventStore.aggregateProperties(
> appName = dsp.appName,
> entityType = "item")(sc)
> 
> to execute in parallel
> 
> The PEventStore calls from 2 separate closures start hitting HBase and it 
> fails, no matter how high I set the RPC and Scanner Timeout. 
> 
> This has only come up recently with some restructuring, which I assume caused 
> the 2 tasks to end up at the same point in the DAG. Is there a way to force 
> one HBase related task to complete before the other is started? They both 
> return RDDs, which are lazy evaluated like promises until the data is needed. 
> Can I force the promise to be kept?
> 

Re: clashing hbase queries

[Andrew Purtell]

This sounds like hotspotting. Ideally the workload over the keyspace can be 
better distributed, which is another avenue of attack - partitioning, keying 
strategy.  


> On Oct 13, 2016, at 6:10 PM, Pat Ferrel  wrote:
> 
> The DAG for a template just happens to schedule 2 tasks that do something 
> like this:
> 
> val fieldsRDD: RDD[(ItemID, PropertyMap)] = PEventStore.aggregateProperties(
>  appName = dsp.appName,
>  entityType = "item")(sc)
> 
> to execute in parallel
> 
> The PEventStore calls from 2 separate closures start hitting HBase and it 
> fails, no matter how high I set the RPC and Scanner Timeout. 
> 
> This has only come up recently with some restructuring, which I assume caused 
> the 2 tasks to end up at the same point in the DAG. Is there a way to force 
> one HBase related task to complete before the other is started? They both 
> return RDDs, which are lazy evaluated like promises until the data is needed. 
> Can I force the promise to be kept?
> 

clashing hbase queries

[Pat Ferrel]

The DAG for a template just happens to schedule 2 tasks that do something like 
this:

val fieldsRDD: RDD[(ItemID, PropertyMap)] = PEventStore.aggregateProperties(
  appName = dsp.appName,
  entityType = "item")(sc)

to execute in parallel

The PEventStore calls from 2 separate closures start hitting HBase and it 
fails, no matter how high I set the RPC and Scanner Timeout. 

This has only come up recently with some restructuring, which I assume caused 
the 2 tasks to end up at the same point in the DAG. Is there a way to force one 
HBase related task to complete before the other is started? They both return 
RDDs, which are lazy evaluated like promises until the data is needed. Can I 
force the promise to be kept?