Alexei, >> stopping fragmented node and removing partition data, then starting it again
That's exactly what we're doing to solve the fragmentation issue. The problem here is that we have to perform N/B restart-rebalance operations (N - cluster size, B - backups count) and it takes a lot of time with risks to lose the data. On Fri, Sep 27, 2019 at 5:49 PM Alexei Scherbakov < alexey.scherbak...@gmail.com> wrote: > Probably this should be allowed to do using public API, actually this is > same as manual rebalancing. > > пт, 27 сент. 2019 г. в 17:40, Alexei Scherbakov < > alexey.scherbak...@gmail.com>: > > > The poor man's solution for the problem would be stopping fragmented node > > and removing partition data, then starting it again allowing full state > > transfer already without deletes. > > Rinse and repeat for all owners. > > > > Anton Vinogradov, would this work for you as workaround ? > > > > чт, 19 сент. 2019 г. в 13:03, Anton Vinogradov <a...@apache.org>: > > > >> Alexey, > >> > >> Let's combine your and Ivan's proposals. > >> > >> >> vacuum command, which acquires exclusive table lock, so no concurrent > >> activities on the table are possible. > >> and > >> >> Could the problem be solved by stopping a node which needs to be > >> defragmented, clearing persistence files and restarting the node? > >> >> After rebalancing the node will receive all data back without > >> fragmentation. > >> > >> How about to have special partition state SHRINKING? > >> This state should mean that partition unavailable for reads and updates > >> but > >> should keep it's update-counters and should not be marked as lost, > renting > >> or evicted. > >> At this state we able to iterate over the partition and apply it's > entries > >> to another file in a compact way. > >> Indices should be updated during the copy-on-shrink procedure or at the > >> shrink completion. > >> Once shrank file is ready we should replace the original partition file > >> with it and mark it as MOVING which will start the historical rebalance. > >> Shrinking should be performed during the low activity periods, but even > in > >> case we found that activity was high and historical rebalance is not > >> suitable we may just remove the file and use regular rebalance to > restore > >> the partition (this will also lead to shrink). > >> > >> BTW, seems, we able to implement partition shrink in a cheap way. > >> We may just use rebalancing code to apply fat partition's entries to the > >> new file. > >> So, 3 stages here: local rebalance, indices update and global historical > >> rebalance. > >> > >> On Thu, Sep 19, 2019 at 11:43 AM Alexey Goncharuk < > >> alexey.goncha...@gmail.com> wrote: > >> > >> > Anton, > >> > > >> > > >> > > >> The solution which Anton suggested does not look easy because it > >> will > >> > > most likely significantly hurt performance > >> > > Mostly agree here, but what drop do we expect? What price do we > ready > >> to > >> > > pay? > >> > > Not sure, but seems some vendors ready to pay, for example, 5% drop > >> for > >> > > this. > >> > > >> > 5% may be a big drop for some use-cases, so I think we should look at > >> how > >> > to improve performance, not how to make it worse. > >> > > >> > > >> > > > >> > > >> it is hard to maintain a data structure to choose "page from > >> free-list > >> > > with enough space closest to the beginning of the file". > >> > > We can just split each free-list bucket to the couple and use first > >> for > >> > > pages in the first half of the file and the second for the last. > >> > > Only two buckets required here since, during the file shrink, first > >> > > bucket's window will be shrank too. > >> > > Seems, this give us the same price on put, just use the first bucket > >> in > >> > > case it's not empty. > >> > > Remove price (with merge) will be increased, of course. > >> > > > >> > > The compromise solution is to have priority put (to the first path > of > >> the > >> > > file), with keeping removal as is, and schedulable per-page > migration > >> for > >> > > the rest of the data during the low activity period. > >> > > > >> > Free lists are large and slow by themselves, it is expensive to > >> checkpoint > >> > and read them on start, so as a long-term solution I would look into > >> > removing them. Moreover, not sure if adding yet another background > >> process > >> > will improve the codebase reliability and simplicity. > >> > > >> > If we want to go the hard path, I would look at free page tracking > >> bitmap - > >> > a special bitmask page, where each page in an adjacent block is marked > >> as 0 > >> > if it has free space more than a certain configurable threshold (say, > >> 80%) > >> > - free, and 1 if less (full). Some vendors have successfully > implemented > >> > this approach, which looks much more promising, but harder to > implement. > >> > > >> > --AG > >> > > >> > > > > > > -- > > > > Best regards, > > Alexei Scherbakov > > > > > -- > > Best regards, > Alexei Scherbakov >
