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From "Eric Newton (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-4112) MinC start/stop updates are always hsync'd
Date Thu, 21 Jan 2016 16:47:39 GMT


Eric Newton commented on ACCUMULO-4112:

I ran another set of experiments, trying to determine the basic costs of SYNC over LOG Durabilities
for lots of MinCs.

The main determining factor for speed was using a "reasonable" IMM.  Using 100k IMM for 10
tablets (plus the metadata tablets), leaves less than 10k per tablet. By simply increasing
the IMM to 200k, performance is improved (and, probably fewer MinCs occurred).

So, I've been unable to reproduce the issue that [~kturner] experienced with Fluo in a small
test.  But I have learned that there is a bare minimum IMM size required for a given number
of tablets.  And that's 10-20K for each hosted tablet.  These are easily affordable on any
modern computer even with 1000 tablets.

I've attached an image with the numbers (sorry, but that's easier than trying to format the
wiki markup).

> MinC start/stop updates are always hsync'd
> ------------------------------------------
>                 Key: ACCUMULO-4112
>                 URL:
>             Project: Accumulo
>          Issue Type: Bug
>          Components: tserver
>         Environment: Fluo testing on a 20-node cluster
>            Reporter: Eric Newton
>            Assignee: Eric Newton
>            Priority: Minor
>         Attachments: HSyncOverheadExperiment.png,, Sync-Flush-Log-Performance.png
>          Time Spent: 10m
>  Remaining Estimate: 0h
> [~kturner] writes:
> {quote}
> I was running a Fluo test with 1.8.0-SNAP on my workstation.  My Fluo table had a ton
of tablets.   I was seeing terrible performance.   I started looking at the tserver and noticed
it was always calling hsync.  I tracked down the problem to the fact that when minc start
and stop events are written to the log they are always written w/ sync level.   My poor little
tserver was constantly minor compacting (probably had around 600 tablets that were all being
written to).  
> I changed the test config to create like 15 tablets and the performance was much better.
 All cores were 100% utilized, which was not the case when hsync was always called.
> {quote}

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