If we use 0 to indicate immediate compaction, the compaction lag is determined by segment.ms in worst case. If segment.ms is 24 hours, "immediate compaction" is a weaker guarantee than setting any value less than 24 hours. By the definition of "max compaction lag", we cannot have zero lag. So I use 0 to indicate "disable".
Xiongqi (Wesley) Wu On Wed, Sep 5, 2018 at 8:34 AM Colin McCabe <cmcc...@apache.org> wrote: > On Tue, Sep 4, 2018, at 22:11, Brett Rann wrote: > > > That's a fair point. We should make 0 = disable, to be consistent with > > the other settings. > > > > -1 is used elsewhere for disable and when seeing it in a config it's > clear > > that it's a special meaning. 0 doesn't have to mean instant, it just > means > > as quickly as possible. I don't think 0 is intuitive for disabled and it > > will be confusing. I wasn't aware segment.ms=0 == disabled, but I think > > that is also unintuitive. > > I think there is an argument for keeping these two configurations > consistent, since they are so similar. I agree that 0 was an unfortunate > choice., > > best, > Colin > > > > > On Wed, Sep 5, 2018 at 11:38 AM Colin McCabe <cmcc...@apache.org> wrote: > > > > > On Tue, Sep 4, 2018, at 17:47, xiongqi wu wrote: > > > > Colin, > > > > Thank you for comments. > > > > see my inline reply below. > > > > > > > > Xiongqi (Wesley) Wu > > > > > > > > > > > > On Tue, Sep 4, 2018 at 5:24 PM Colin McCabe <cmcc...@apache.org> > wrote: > > > > > > > > > Hi Xiongqi, > > > > > > > > > > Thanks for this KIP. > > > > > > > > > > The name seems a bit ambiguous. Our compaction policies are already > > > > > time-based, after all. It seems like this change is focused around > > > adding > > > > > a “max.compaction.lag.ms." Perhaps the KIP title should be > something > > > > > like "add maximum compaction lag time"? > > > > > > > > > > ==========> sure. I will change the title. > > > > > > > > > The active segment is forced to roll when either " > > > max.compaction.lag.ms" > > > > > > or "segment.ms" (log.roll.ms and log.roll.hours) has reached. > > > > > > > > > > If the max.compaction.lag.ms is low, it seems like segments will > be > > > > > rolled very frequently. This can be a source of problems in the > > > cluster, > > > > > since creating many different small log segments consumes a huge > > > amount of > > > > > cluster resources. Therefore, I would suggest adding a broker-level > > > > > configuration which allows us to set a minimum value for > > > > > max.compaction.lag.ms. If we let users set it on a per-topic > basis, > > > > > someone could set a value of 1 ms or something, and cause chaos. > > > > > > > > > > =========> this applies to segment.ms as well. Today users can > set " > > > > segment.ms" to a very low value, and cause a frequent rolling of > active > > > > segments. > > > > > > Hi Xiongqi, > > > > > > I agree that this is an existing problem with segment.ms. However, > that > > > doesn't mean that we shouldn't fix it. As you noted, there will be more > > > interest in these topic-level retention settings as a result of GDPR. > It > > > seems likely that pre-existing problems will cause more trouble. > > > > > > The fix seems relatively straightforward here -- add a broker-level > > > minimum segment.ms that overrides per-topic minimums. We can also fail > > > with a helpful error message when someone attempts to set an invalid > > > configuration. > > > > > > > In my option, the minimum of "max.compaction.lag.ms" should be > > > > based on the minimum of "segment.ms". Since today the minimum of > > > segment.ms > > > > is 1, "max.compaction.lag.ms" also starts with 1. "0" means > disable. I > > > > can use -1 as disable, but it is hard to define the meaning of 0 > because > > > we > > > > cannot just roll the active segment immediately. > > > > > > That's a fair point. We should make 0 = disable, to be consistent with > the > > > other settings. > > > > > > best, > > > Colin > > > > > > > > > > > > -- Note that an alternative configuration is to use -1 as > "disabled" > > > and > > > > > 0 > > > > > > as "immediate compaction". Because compaction lag is still > determined > > > > > > based on min.compaction.lag and how long to roll an active > segment, > > > > > the > > > > > > actual lag for compaction is undetermined if we use "0". On the > other > > > > > > hand, we can already set "min.cleanable.dirty.ratio" to achieve > the > > > > > same > > > > > > goal. So here we choose "0" as "disabled". > > > > > > > > > > I would prefer -1 to be the invalid setting. Treating 0 differently > > > than > > > > > 1 seems strange to me. > > > > > > > > > > =====> see my previous comment, I am not strongly against, but 0 is > > > not a > > > > valid configuration in my option. So I use "0" as disabled state. > > > > > > > > best, > > > > > Colin > > > > > > > > > > > > > > > On Tue, Sep 4, 2018, at 15:04, xiongqi wu wrote: > > > > > > Let's VOTE for this KIP. > > > > > > KIP: > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-354 > > > <https://cwiki.apache.org/confluence/display/KAFKA/KIP-354> > > > > > > %3A+Time-based+log+compaction+policy > > > > > > > > > > > > Implementation: > > > > > > > > > > > > https://github.com/apache/kafka/pull/5611 > > > <https://github.com/apache/kafka/pull/5611> > > > > > > > > > > > > > > > > > > > > > > > > Xiongqi (Wesley) Wu > > > > > > > > >
