Hi,
I think that it’s actually quite common to have multiple iodevices.
Even if there is only one disk, configuring multiple iodevices can
improve performance - especially if a significant part of the data fits
into memory (and disk IO is not the limiting factor). And the reason
for that seems to be that the degree of parallelism for the "lower"
part of a query plan is limited by the number of available iodevices.
Also, I think that multiple disks are not uncommon for heavier data
management workloads. The d2 instances [1] on AWS give some example
configurations.
All this is just to say that we should not discount
a) the need to support multiple disks and
b) the limitations to linear scalability introduced by "1-per-NC" (vs.
"1-per-partition") objects.
On machines with a few more cores (10+) we've used multiple NCs (as
opposed to multiple partitions per NC) to achieve better scale-out and
better query performance.
Cheers,
Till
[1]
https://aws.amazon.com/about-aws/whats-new/2015/03/now-available-d2-instances-the-latest-generation-of-amazon-ec2-dense-storage-instances/
On 23 Oct 2017, at 20:18, Chen Luo wrote:
I was confusing about this problem last quarter, and I remembered
(maybe
Ian) told me the same reason that it's mainly used for memory
budgeting
(primary and secondary indexes of dataset in the same node). Moreover,
it's
not very common to have too many I/O devices on a node, unless it has
multiple disks.
Best regards,
Chen Luo
On Mon, Oct 23, 2017 at 8:12 PM, Sattam Alsubaiee
<[email protected]>
wrote:
There is a fundamental reason behind that (unless that has changed).
All
partitions of a dataset (primary and secondary indexes) share the
memory
budget for their in-memory components. So they use the same optracker
to
synchronize their operations.
Sattam
On Oct 24, 2017 5:59 AM, "Wail Alkowaileet" <[email protected]>
wrote:
Thanks Abdullah!
On Mon, Oct 23, 2017 at 7:15 PM, abdullah alamoudi
<[email protected]>
wrote:
Hi Wail,
There is no fundamental reason why it is one. In fact, it has been
on
our
todo for a long time to make it one per partition.
Cheers,
Abdullah.
On Oct 23, 2017, at 7:14 PM, Wail Alkowaileet <[email protected]>
wrote:
Dear devs,
I have a question regarding the opTracker. Currently, we
initialize
one
opTracker per dataset in every NC.
My question is why it's per dataset not per partition ? Is there a
transactional constraints for that ?
From what I can see that the opTracker can create a lot of
contention
in
case there're many IO devices. For instance, each insert will call
*LSMHarness.getAndEnterComponents()* [1], which
*synchronize(opTracker). *That
means (correct me if I'm wrong), insert is going to serialize the
*enterComponent()* part among partitions.
[1]
https://github.com/apache/asterixdb/blob/master/hyracks-
fullstack/hyracks/hyracks-storage-am-lsm-common/src/
main/java/org/apache/hyracks/storage/am/lsm/common/impls/
LSMHarness.java#L86
--
*Regards,*
Wail Alkowaileet
--
*Regards,*
Wail Alkowaileet
