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From Jerven Tjalling Bolleman <jerven.bolle...@sib.swiss>
Subject Re: Static index, fastest way to do forceMerge
Date Tue, 18 Dec 2018 10:10:07 GMT
Hi Dawid,

Thanks for looking into this! I have been distracted with other work and
did not get the time I expected to work on it.

Regards,
Jerven
On 11/30/18 12:01 PM, Dawid Weiss wrote:
> Just FYI: I implemented a quick and dirty PoC to see what it'd work
> like. Not much of a difference on my machine (since postings merging
> dominates everything else). Interesting problem how to split it up to
> saturate all of available resources though (CPU and I/O).
> 
> https://issues.apache.org/jira/browse/LUCENE-8580
> 
> Dawid
> 
> On Fri, Nov 2, 2018 at 10:17 PM Dawid Weiss <dawid.weiss@gmail.com> wrote:
>>
>> Thanks for chipping in, Toke. A ~1TB index is impressive.
>>
>> Back of the envelope says reading & writing 900GB in 8 hours is
>> 2*900GB/(8*60*60s) = 64MB/s. I don't remember the interface for our
>> SSD machine, but even with SATA II this is only ~1/5th of the possible
>> fairly sequential IO throughput. So for us at least, NVMe drives are
>> not needed to have single-threaded CPU as bottleneck.
>>
>> The mileage will vary depending on the CPU -- if it can merge the data
>> from multiple files at ones fast enough then it may theoretically
>> saturate the bandwidth... but I agree we also seem to be CPU bound on
>> these N-to-1 merges, a regular SSD is enough.
>>
>>> And +1 to the issue BTW.
>>
>> I agree. Fine-grained granularity here would be a win even in the
>> regular "merge is a low-priority citizen" case. At least that's what I
>> tend to think. And if there are spare CPUs, the gain would be
>> terrific.
>>
>> Dawid
> 
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