-Re: quick question about the new SE iface
David Alves 2013-04-20, 23:21
Thanks for the quick reply and for the pointers.
wrt to question one, now thinking about it that opens the door for some cool optimizations.
wrt to question two I found a couple of interesting references using MMAP'd tmpfs, was now looking into the way JCuda uses pinned memory.
i'll also look into the Peter Lawrey references.
On Apr 20, 2013, at 6:00 PM, Jacques Nadeau <[EMAIL PROTECTED]> wrote:
> On Sat, Apr 20, 2013 at 2:39 PM, David Alves <[EMAIL PROTECTED]> wrote:
>> I'm porting the region level HBase SE to the new SE iface and I
>> have a couple of questions.
>> 1- about the method: public ListMultimap<ReadEntry,
>> DrillbitEndpoint> getReadLocations(Collection<ReadEntry> entries)
>> when does it happen that a read entry gets assigned more that one
>> in terms of hbase I can see the case where multiple read entries
>> get assigned to the same drillbit (co-located regions) but I can't envision
>> a case where the same read entry (usually corresponding to a shard or
>> partition) gets assigned to multiple drillbits. when can that happen?
> Best example is probably block replica locations in HDFS have multiple
> possible endpoints.
>> 2- with regard to off-heap storage and underlying SE co-location
>> this is not really a doubt, just checking that my reasoning is
>> correct before.
>> for co-located underlying SE and Drillbit's we should use
>> off-heap, shared memory for IPC when possible, correct?
>> Specifically I'm investigating the possibility of having HBase
>> store region scan data directly off heap and making the results from hbase
>> contain a set references to aligned shared memory locations.
>> I'm not sure I'll be implementing this immediately but I'd like to
>> design accounting for it if that is the idea.
>> Also this means that SE's must work in two modes: co-located with
>> shared memory and remote with sockets. We'd then have the
>> Jacques: I'm sure you've put some thought to the underlying
>> mechanics on how to accomplish this, could you share some quick
> The challenge is separate JVMs don't have a nice way to share memory. The
> simplest way is probably using MMAP'd tmpfs. We'd have to evaluate the
> performance impact of this complexity. I think the Java Chronicle,
> HugeCollections or VanillaJava stuff by Peter Lawrey has played with this.
> There isn't a lot of work in the space. Other interesting info:
> Yes, this does mean that an SE may need to use two different mechanisms to
> interact: one local and one remote/fallback.