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https://issues.apache.org/jira/browse/LUCENE-10448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17502076#comment-17502076
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kkewwei edited comment on LUCENE-10448 at 3/7/22, 9:25 AM:
-----------------------------------------------------------
[~vigyas] [~jpountz] I count the burst write rate of no-pause bytes with high
pressure of writing:
{code:java}
[2022-03-07T08:23:05,864][DEBUG][o.e.i.e.I.EngineMergeScheduler] [node1]
[index1][26] merge segment [_43a] done: took [25.2s], [317.8 MB], [176,633
docs], [0s stopped], [19.8s throttled], [625.8 MB written], [29.2 MB/sec
throttle], [callTimes=852],[ignorePauseTimes=49], [detailBytes(mb) =
[0.7422037, 0.73268795, 0.7350941, 0.730608, 0.7306595, 0.7303219, 0.7305584,
0.73028755, 0.7304802, 0.73048687, 0.7303219, 0.73038864, 0.73030186,
0.7305927, 0.7303219, 0.73028755, 0.73043823, 0.7314129, 0.73110104, 0.7306318,
0.7303457, 0.7315569, 0.731061, 0.73035717, 0.73029804, 0.73031235, 0.7302904,
0.7303295, 0.73033714, 0.7304115, 0.7304363, 0.73035145, 0.7303152, 0.7303295,
0.7309208, 0.73061085, 0.7315531, 0.7372618, 0.734375, 0.734375, 0.734375,
0.73813057, 0.734375, 0.7342024, 0.734375, 0.734375, 0.734375, 0.734375,
0.734375]], [detailRate(mb/s) = [2.75478E-8, 2.3733156, 3.8783703,
2.7117402E-8, 2.7119311E-8, 2.710678E-8, 2.711556E-8, 2.7105507E-8, 4.484641,
3.1927187, 2.4854445, 2.0364974, 1.722687, 1.4875951, 1.2919687, 2.7105507E-8,
0.98034406, 0.9306443, 0.8845948, 0.8425208, 0.80407506, 0.77062935, 0.7450095,
2.7108092E-8, 4.1841693, 1.4971824, 16.385893, 4.7222166, 1.9614059, 7.041826,
8.008545, 2.534279, 17.670755, 6.7497787, 2.7129008E-8, 19.349627, 26.39924,
16.710173, 5.9312387, 12.802376, 10.644308, 4.5160117, 14.152909, 2.8590457,
460.67938, 432.62634, 92.555466, 290.15073, 12.046124]],
[biggerThanLimitedRate(mb/s) = [460.67938, 432.62634, 92.555466, 290.15073]]
{code}
*callTimes=852* means that MergeRateLimiter.pause is called 852 times.
*ignorePauseTimes=49* means that there are 49 no-pause times in 852 times.
*detailBytes(mb)* means the detail no-pause bytes, total count is 49.
*detailRate(mb/s)* means the detail instant rate of the 49 *detailBytes*.
*biggerThanLimitedRate(mb/s)*: means the instant rate bigger than limited
rate(29.2 MB/sec throttle), we can see that the max instant rate is
460.67938mb/s, which is 10 times the limited rate.
The burst write rate (in addition to/ instead of) the no-pause-write frequency
is about 0-10%, It depends on the writing pressure, In my test, the write
thread is relatively busy.
This is how I count the statistics.
{code:java}
@Override
public void writeBytes(byte[] b, int offset, int length) throws IOException {
if (bytesSinceLastPause == 0) {
// writing time start at writing
startTime = System.nanoTime();
}
bytesSinceLastPause += length;
delegate.writeBytes(b, offset, length);
checkRate();
}
private void checkRate() throws IOException {
if (bytesSinceLastPause > currentMinPauseCheckBytes) {
// count the lasted time.
rateLimiter.pause(bytesSinceLastPause, (System.nanoTime())- startTime);
bytesSinceLastPause = 0;
currentMinPauseCheckBytes = rateLimiter.getMinPauseCheckBytes();
}
}
{code}
with the lasted time and writing bytes, It's easy to compute the instant rate.
was (Author: kkewwei):
[~vigyas] I count the burst write rate of no-pause bytes with high pressure of
writing:
{code:java}
[2022-03-07T08:23:05,864][DEBUG][o.e.i.e.I.EngineMergeScheduler] [node1]
[index1][26] merge segment [_43a] done: took [25.2s], [317.8 MB], [176,633
docs], [0s stopped], [19.8s throttled], [625.8 MB written], [29.2 MB/sec
throttle], [callTimes=852],[ignorePauseTimes=49], [detailBytes(mb) =
[0.7422037, 0.73268795, 0.7350941, 0.730608, 0.7306595, 0.7303219, 0.7305584,
0.73028755, 0.7304802, 0.73048687, 0.7303219, 0.73038864, 0.73030186,
0.7305927, 0.7303219, 0.73028755, 0.73043823, 0.7314129, 0.73110104, 0.7306318,
0.7303457, 0.7315569, 0.731061, 0.73035717, 0.73029804, 0.73031235, 0.7302904,
0.7303295, 0.73033714, 0.7304115, 0.7304363, 0.73035145, 0.7303152, 0.7303295,
0.7309208, 0.73061085, 0.7315531, 0.7372618, 0.734375, 0.734375, 0.734375,
0.73813057, 0.734375, 0.7342024, 0.734375, 0.734375, 0.734375, 0.734375,
0.734375]], [detailRate(mb/s) = [2.75478E-8, 2.3733156, 3.8783703,
2.7117402E-8, 2.7119311E-8, 2.710678E-8, 2.711556E-8, 2.7105507E-8, 4.484641,
3.1927187, 2.4854445, 2.0364974, 1.722687, 1.4875951, 1.2919687, 2.7105507E-8,
0.98034406, 0.9306443, 0.8845948, 0.8425208, 0.80407506, 0.77062935, 0.7450095,
2.7108092E-8, 4.1841693, 1.4971824, 16.385893, 4.7222166, 1.9614059, 7.041826,
8.008545, 2.534279, 17.670755, 6.7497787, 2.7129008E-8, 19.349627, 26.39924,
16.710173, 5.9312387, 12.802376, 10.644308, 4.5160117, 14.152909, 2.8590457,
460.67938, 432.62634, 92.555466, 290.15073, 12.046124]],
[biggerThanLimitedRate(mb/s) = [460.67938, 432.62634, 92.555466, 290.15073]]
{code}
*callTimes=852* means that MergeRateLimiter.pause is called 852 times.
*ignorePauseTimes=49* means that there are 49 no-pause times in 852 times.
*detailBytes(mb)* means the detail no-pause bytes, total count is 49.
*detailRate(mb/s)* means the detail instant rate of the 49 *detailBytes*.
*biggerThanLimitedRate(mb/s)*: means the instant rate bigger than limited
rate(29.2 MB/sec throttle), we can see that the max instant rate is
460.67938mb/s, which is 10 times the limited rate.
The burst write rate (in addition to/ instead of) the no-pause-write frequency
is about 0-10%, It depends on the writing pressure, In my test, the write
thread is relatively busy.
This is how I count the statistics.
{code:java}
@Override
public void writeBytes(byte[] b, int offset, int length) throws IOException {
if (bytesSinceLastPause == 0) {
// writing time start at writing
startTime = System.nanoTime();
}
bytesSinceLastPause += length;
delegate.writeBytes(b, offset, length);
checkRate();
}
private void checkRate() throws IOException {
if (bytesSinceLastPause > currentMinPauseCheckBytes) {
// count the lasted time.
rateLimiter.pause(bytesSinceLastPause, (System.nanoTime())- startTime);
bytesSinceLastPause = 0;
currentMinPauseCheckBytes = rateLimiter.getMinPauseCheckBytes();
}
}
{code}
with the lasted time and writing bytes, It's easy to compute the instant rate.
> MergeRateLimiter doesn't always limit instant rate.
> ---------------------------------------------------
>
> Key: LUCENE-10448
> URL: https://issues.apache.org/jira/browse/LUCENE-10448
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/other
> Affects Versions: 8.11.1
> Reporter: kkewwei
> Priority: Major
>
> We can see the code in *MergeRateLimiter*:
> {code:java}
> private long maybePause(long bytes, long curNS) throws
> MergePolicy.MergeAbortedException {
>
> double rate = mbPerSec;
> double secondsToPause = (bytes / 1024. / 1024.) / rate;
> long targetNS = lastNS + (long) (1000000000 * secondsToPause);
> long curPauseNS = targetNS - curNS;
> // We don't bother with thread pausing if the pause is smaller than 2
> msec.
> if (curPauseNS <= MIN_PAUSE_NS) {
> // Set to curNS, not targetNS, to enforce the instant rate, not
> // the "averaged over all history" rate:
> lastNS = curNS;
> return -1;
> }
> ......
> }
> {code}
> If a Segment is been merged, *maybePause* is called in 7:00, lastNS=7:00,
> then the *maybePause* is called in 7:05 again, so the value of
> *targetNS=lastNS + (long) (1000000000 * secondsToPause)* must be smaller than
> *curNS*, no matter how big the bytes is, we will return -1 and ignore to
> pause.
> I count the total times(callTimes) calling *maybePause* and ignored pause
> times(ignorePauseTimes) and detail ignored bytes(detailBytes):
> {code:java}
> [2022-03-02T15:16:51,972][DEBUG][o.e.i.e.I.EngineMergeScheduler] [node1]
> [index1][21] merge segment [_4h] done: took [26.8s], [123.6 MB], [61,219
> docs], [0s stopped], [24.4s throttled], [242.5 MB written], [11.2 MB/sec
> throttle], [callTimes=857], [ignorePauseTimes=25], [detailBytes(mb) =
> [0.28899956, 0.28140354, 0.28015518, 0.27990818, 0.2801447, 0.27991104,
> 0.27990723, 0.27990913, 0.2799101, 0.28010082, 0.2799921, 0.2799673,
> 0.28144264, 0.27991295, 0.27990818, 0.27993107, 0.2799387, 0.27998447,
> 0.28002167, 0.27992058, 0.27998066, 0.28098202, 0.28125, 0.28125, 0.28125]]
> {code}
> There are 857 times calling *maybePause*, including 25 times which is ignored
> to pause, we can see that the ignored detail bytes (such as 0.28125mb) are
> not small.
> As long as the interval between two *maybePause* calls is relatively long,
> the pause action that should be executed will not be executed.
>
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