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https://issues.apache.org/jira/browse/HBASE-13686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14552301#comment-14552301
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Ashish Singhi commented on HBASE-13686:
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The work of refillStrategy.refill is to give the number of resources that are
refilled and that can then be checked and added to the existing avail to form a
new avail.
bq. The canExecute() should not to handle the special case of refillStrategy
All the special case of refillStrategy is handled by themselves in {{refill}}
method {{canExecute}} has only the code which will be common to all the
refillStrategy after they finish calculating the refill amount and can avoid
duplicating the code.
{quote}
Assume there is a RateLimiter which limit and avail is Long.MAX_VALUE. Then
consume(1). The avail will be Long.MAX_VALUE - 1. After a long time,
canExecute(1) again. This will refill again. The delta will be much greater
than 1. Then available + delta will be negative.
{quote}
This you have already answered in your first comment that **"check positive
overflow" can catch this case**. So I feel better to leave this piece of code
in {{canExecute}} only and avoid duplicating this code in each refill method as
of now.
I do not see any strong reason to move this code in {{refill}} of each
{{RefillStrategy}}
> Fail to limit rate in RateLimiter
> ---------------------------------
>
> Key: HBASE-13686
> URL: https://issues.apache.org/jira/browse/HBASE-13686
> Project: HBase
> Issue Type: Bug
> Affects Versions: 2.0.0, 1.1.0
> Reporter: Guanghao Zhang
> Assignee: Ashish Singhi
> Fix For: 2.0.0, 1.2.0, 1.1.1
>
> Attachments: HBASE-13686.patch
>
>
> While using the patch in HBASE-11598 , I found that RateLimiter can't to
> limit the rate right.
> {code}
> /**
> * given the time interval, are there enough available resources to allow
> execution?
> * @param now the current timestamp
> * @param lastTs the timestamp of the last update
> * @param amount the number of required resources
> * @return true if there are enough available resources, otherwise false
> */
> public synchronized boolean canExecute(final long now, final long lastTs,
> final long amount) {
> return avail >= amount ? true : refill(now, lastTs) >= amount;
> }
> {code}
> When avail >= amount, avail can't be refill. But in the next time to call
> canExecute, lastTs maybe update. So avail will waste some time to refill.
> Even we use smaller rate than the limit, the canExecute will return false.
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