Alexey, Sounds good to me.
On Thu, Oct 3, 2019 at 10:51 AM Alexey Goncharuk <alexey.goncha...@gmail.com> wrote: > Anton, > > Switching a partition to and from the SHRINKING state will require > intricate synchronizations in order to properly determine the start > position for historical rebalance without PME. > > I would still go with an offline-node approach, but instead of cleaning the > persistence, we can do effective defragmentation when the node is offline > because we are sure that there is no concurrent load. After the > defragmentation completes, we bring the node back to the cluster and > historical rebalance will kick in automatically. It will still require > manual node restarts, but since the data is not removed, there are no > additional risks. Also, this will be an excellent solution for those who > can afford downtime and execute the defragment command on all nodes in the > cluster simultaneously - this will be the fastest way possible. > > --AG > > пн, 30 сент. 2019 г. в 09:29, Anton Vinogradov <a...@apache.org>: > > > 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 > > > > > >
