Hi, all, FYI, I have updated the PIP [1].
Main changes: - Use new name `tag` - Enrich Motivation - New Section `Data Files Handling` to describe how to determine a data files can be deleted. Best, Yu Zelin [1] https://cwiki.apache.org/confluence/x/NxE0Dw > 2023年5月24日 17:18，yu zelin <[email protected]> 写道： > > Hi, Guojun, > > I’d like to share my thoughts about your questions. > > 1. Expiration of savepoint > In my opinion, savepoints are created in a long interval, so there will not > exist too many of them. > If users create a savepoint per day, there are 365 savepoints a year. So I > didn’t consider expiration > of it, and I think provide a flink action like `delete-savepoint id = 1` is > enough now. > But if it is really important, we can introduce table options to do so. I > think we can do it like expiring > snapshots. > > 2. > id of compacted snapshot picked by the savepoint > My initial idea is picking a compacted snapshot or doing compaction before > creating savepoint. But > After discuss with Jingsong, I found it’s difficult. So now I suppose to > directly create savepoint from > the given snapshot. Maybe we can optimize it later. > The changes will be updated soon. >> manifest file list in system-table > I think manifest file is not very important for users. Users can find when a > savepoint is created, and > get the savepoint id, then they can query it from the savepoint by the id. I > did’t see what scenario > the users need the manifest file information. What do you think? > > Best, > Yu Zelin > >> 2023年5月24日 10:50，Guojun Li <[email protected]> 写道： >> >> Thanks zelin for bringing up the discussion. I'm thinking about: >> 1. How to manage the savepoints if there are no expiration mechanism, by >> the TTL management of storages or external script? >> 2. I think the id of compacted snapshot picked by the savepoint and >> manifest file list is also important information for users, could these >> information be stored in the system-table? >> >> Best, >> Guojun >> >> On Mon, May 22, 2023 at 9:13 PM Jingsong Li <[email protected]> wrote: >> >>> FYI >>> >>> The PIP lacks a table to show Discussion thread & Vote thread & ISSUE... >>> >>> Best >>> Jingsong >>> >>> On Mon, May 22, 2023 at 4:48 PM yu zelin <[email protected]> wrote: >>>> >>>> Hi, all, >>>> >>>> Thank all of you for your suggestions and questions. After reading your >>> suggestions, I adopt some of them and I want to share my opinions here. >>>> >>>> To make my statements more clear, I will still use the word `savepoint`. >>> When we make a consensus, the name may be changed. >>>> >>>> 1. The purposes of savepoint >>>> >>>> As Shammon mentioned, Flink and database also have the concept of >>> `savepoint`. So it’s better to clarify the purposes of our savepoint. >>> Thanks for Nicholas and Jingsong, I think your explanations are very clear. >>> I’d like to give my summary: >>>> >>>> (1) Fault recovery (or we can say disaster recovery). Users can ROLL >>> BACK to a savepoint if needed. If user rollbacks to a savepoint, the table >>> will hold the data in the savepoint and the data committed after the >>> savepoint will be deleted. In this scenario we need savepoint because >>> snapshots may have expired, the savepoint can keep longer and save user’s >>> old data. >>>> >>>> (2) Record versions of data at a longer interval (typically daily level >>> or weekly level). With savepoint, user can query the old data in batch >>> mode. Comparing to copy records to a new table or merge incremental records >>> with old records (like using merge into in Hive), the savepoint is more >>> lightweight because we don’t copy data files, we just record the meta data >>> of them. >>>> >>>> As you can see, savepoint is very similar to snapshot. The differences >>> are: >>>> >>>> (1) Savepoint lives longer. In most cases, snapshot’s life time is >>> about several minutes to hours. We suppose the savepoint can live several >>> days, weeks, or even months. >>>> >>>> (2) Savepoint is mainly used for batch reading for historical data. In >>> this PIP, we don’t introduce streaming reading for savepoint. >>>> >>>> 2. Candidates of name >>>> >>>> I agree with Jingsong that we can use a new name. Since the purpose and >>> mechanism (savepoint is very similar to snapshot) of savepoint is similar >>> to `tag` in iceberg, maybe we can use `tag`. >>>> >>>> In my opinion, an alternative is `anchor`. All the snapshots are like >>> the navigation path of the streaming data, and an `anchor` can stop it in a >>> place. >>>> >>>> 3. Public table operations and options >>>> >>>> We supposed to expose some operations and table options for user to >>> manage the savepoint. >>>> >>>> (1) Operations (Currently for Flink) >>>> We provide flink actions to manage savepoints: >>>> create-savepoint: To generate a savepoint from latest snapshot. >>> Support to create from specified snapshot. >>>> delete-savepoint: To delete specified savepoint. >>>> rollback-to: To roll back to a specified savepoint. >>>> >>>> (2) Table options >>>> We suppose to provide options for creating savepoint periodically: >>>> savepoint.create-time: When to create the savepoint. Example: 00:00 >>>> savepoint.create-interval: Interval between the creation of two >>> savepoints. Examples: 2 d. >>>> savepoint.time-retained: The maximum time of savepoints to retain. >>>> >>>> (3) Procedures (future work) >>>> Spark supports SQL extension. After we support Spark CALL statement, we >>> can provide procedures to create, delete or rollback to savepoint for Spark >>> users. >>>> >>>> Support of CALL is on the road map of Flink. In future version, we can >>> also support savepoint-related procedures for Flink users. >>>> >>>> 4. Expiration of data files >>>> >>>> Currently, when a snapshot is expired, data files that not be used by >>> other snapshots. After we introduce the savepoint, we must make sure the >>> data files saved by savepoint will not be deleted. >>>> >>>> Conversely, when a savepoint is deleted, the data files that not be >>> used by existing snapshots and other savepoints will be deleted. >>>> >>>> I have wrote some POC codes to implement it. I will update the mechanism >>> in PIP soon. >>>> >>>> Best, >>>> Yu Zelin >>>> >>>>> 2023年5月21日 20:54，Jingsong Li <[email protected]> 写道： >>>>> >>>>> Thanks Yun for your information. >>>>> >>>>> We need to be careful to avoid confusion between Paimon and Flink >>>>> concepts about "savepoint" >>>>> >>>>> Maybe we don't have to insist on using this "savepoint", for example, >>>>> TAG is also a candidate just like Iceberg [1] >>>>> >>>>> [1] https://iceberg.apache.org/docs/latest/branching/ >>>>> >>>>> Best, >>>>> Jingsong >>>>> >>>>> On Sun, May 21, 2023 at 8:51 PM Jingsong Li <[email protected]> >>> wrote: >>>>>> >>>>>> Thanks Nicholas for your detailed requirements. >>>>>> >>>>>> We need to supplement user requirements in FLIP, which is mainly aimed >>>>>> at two purposes: >>>>>> 1. Fault recovery for data errors (named: restore or rollback-to) >>>>>> 2. Used to record versions at the day level (such as), targeting >>> batch queries >>>>>> >>>>>> Best, >>>>>> Jingsong >>>>>> >>>>>> On Sat, May 20, 2023 at 2:55 PM Yun Tang <[email protected]> wrote: >>>>>>> >>>>>>> Hi Guys, >>>>>>> >>>>>>> Since we use Paimon with Flink in most cases, I think we need to >>> identify the same word "savepoint" in different systems. >>>>>>> >>>>>>> For Flink, savepoint means: >>>>>>> >>>>>>> 1. Triggered by users, not periodically triggered by the system >>> itself. However, this FLIP wants to support it created periodically. >>>>>>> 2. Even the so-called incremental native savepoint [1], it will >>> not depend on the previous checkpoints or savepoints, it will still copy >>> files on DFS to the self-contained savepoint folder. However, from the >>> description of this FLIP about the deletion of expired snapshot files, >>> paimion savepoint will refer to the previously existing files directly. >>>>>>> >>>>>>> I don't think we need to make the semantics of Paimon totally the >>> same as Flink's. However, we need to introduce a table to tell the >>> difference compared with Flink and discuss about the difference. >>>>>>> >>>>>>> [1] >>> https://cwiki.apache.org/confluence/display/FLINK/FLIP-203%3A+Incremental+savepoints#FLIP203:Incrementalsavepoints-Semantic >>>>>>> >>>>>>> Best >>>>>>> Yun Tang >>>>>>> ________________________________ >>>>>>> From: Nicholas Jiang <[email protected]> >>>>>>> Sent: Friday, May 19, 2023 17:40 >>>>>>> To: [email protected] <[email protected]> >>>>>>> Subject: Re: [DISCUSS] PIP-4 Support savepoint >>>>>>> >>>>>>> Hi Guys, >>>>>>> >>>>>>> Thanks Zelin for driving the savepoint proposal. I propose some >>> opinions for savepont: >>>>>>> >>>>>>> -- About "introduce savepoint for Paimon to persist full data in a >>> time point" >>>>>>> >>>>>>> The motivation of savepoint proposal is more like snapshot TTL >>> management. Actually, disaster recovery is very much mission critical for >>> any software. Especially when it comes to data systems, the impact could be >>> very serious leading to delay in business decisions or even wrong business >>> decisions at times. Savepoint is proposed to assist users in recovering >>> data from a previous state: "savepoint" and "restore". >>>>>>> >>>>>>> "savepoint" saves the Paimon table as of the commit time, therefore >>> if there is a savepoint, the data generated in the corresponding commit >>> could not be clean. Meanwhile, savepoint could let user restore the table >>> to this savepoint at a later point in time if need be. On similar lines, >>> savepoint cannot be triggered on a commit that is already cleaned up. >>> Savepoint is synonymous to taking a backup, just that we don't make a new >>> copy of the table, but just save the state of the table elegantly so that >>> we can restore it later when in need. >>>>>>> >>>>>>> "restore" lets you restore your table to one of the savepoint >>> commit. Meanwhile, it cannot be undone (or reversed) and so care should be >>> taken before doing a restore. At this time, Paimon would delete all data >>> files and commit files (timeline files) greater than the savepoint commit >>> to which the table is being restored. >>>>>>> >>>>>>> BTW, it's better to introduce snapshot view based on savepoint, >>> which could improve query performance of historical data for Paimon table. >>>>>>> >>>>>>> -- About Public API of savepont >>>>>>> >>>>>>> Current introduced savepoint interfaces in Public API are not enough >>> for users, for example, deleteSavepoint, restoreSavepoint etc. >>>>>>> >>>>>>> -- About "Paimon's savepoint need to be combined with Flink's >>> savepoint": >>>>>>> >>>>>>> If paimon supports savepoint mechanism and provides savepoint >>> interfaces, the integration with Flink's savepoint is not blocked for this >>> proposal. >>>>>>> >>>>>>> In summary, savepoint is not only used to improve the query >>> performance of historical data, but also used for disaster recovery >>> processing. >>>>>>> >>>>>>> On 2023/05/17 09:53:11 Jingsong Li wrote: >>>>>>>> What Shammon mentioned is interesting. I agree with what he said >>> about >>>>>>>> the differences in savepoints between databases and stream >>> computing. >>>>>>>> >>>>>>>> About "Paimon's savepoint need to be combined with Flink's >>> savepoint": >>>>>>>> >>>>>>>> I think it is possible, but we may need to deal with this in another >>>>>>>> mechanism, because the snapshots after savepoint may expire. We need >>>>>>>> to compare data between two savepoints to generate incremental data >>>>>>>> for streaming read. >>>>>>>> >>>>>>>> But this may not need to block FLIP, it looks like the current >>> design >>>>>>>> does not break the future combination? >>>>>>>> >>>>>>>> Best, >>>>>>>> Jingsong >>>>>>>> >>>>>>>> On Wed, May 17, 2023 at 5:33 PM Shammon FY <[email protected]> >>> wrote: >>>>>>>>> >>>>>>>>> Hi Caizhi, >>>>>>>>> >>>>>>>>> Thanks for your comments. As you mentioned, I think we may need to >>> discuss >>>>>>>>> the role of savepoint in Paimon. >>>>>>>>> >>>>>>>>> If I understand correctly, the main feature of savepoint in the >>> current PIP >>>>>>>>> is that the savepoint will not be expired, and users can perform a >>> query on >>>>>>>>> the savepoint according to time-travel. Besides that, there is >>> savepoint in >>>>>>>>> the database and Flink. >>>>>>>>> >>>>>>>>> 1. Savepoint in database. The database can roll back table data to >>> the >>>>>>>>> specified 'version' based on savepoint. So the key point of >>> savepoint in >>>>>>>>> the database is to rollback data. >>>>>>>>> >>>>>>>>> 2. Savepoint in Flink. Users can trigger a savepoint with a >>> specific >>>>>>>>> 'path', and save all data of state to the savepoint for job. Then >>> users can >>>>>>>>> create a new job based on the savepoint to continue consuming >>> incremental >>>>>>>>> data. I think the core capabilities are: backup for a job, and >>> resume a job >>>>>>>>> based on the savepoint. >>>>>>>>> >>>>>>>>> In addition to the above, Paimon may also face data write >>> corruption and >>>>>>>>> need to recover data based on the specified savepoint. So we may >>> need to >>>>>>>>> consider what abilities should Paimon savepoint need besides the >>> ones >>>>>>>>> mentioned in the current PIP? >>>>>>>>> >>>>>>>>> Additionally, as mentioned above, Flink also has >>>>>>>>> savepoint mechanism. During the process of streaming data from >>> Flink to >>>>>>>>> Paimon, does Paimon's savepoint need to be combined with Flink's >>> savepoint? >>>>>>>>> >>>>>>>>> >>>>>>>>> Best, >>>>>>>>> Shammon FY >>>>>>>>> >>>>>>>>> >>>>>>>>> On Wed, May 17, 2023 at 4:02 PM Caizhi Weng <[email protected]> >>> wrote: >>>>>>>>> >>>>>>>>>> Hi developers! >>>>>>>>>> >>>>>>>>>> Thanks Zelin for bringing up the discussion. The proposal seems >>> good to me >>>>>>>>>> overall. However I'd also like to bring up a few options. >>>>>>>>>> >>>>>>>>>> 1. As Jingsong mentioned, Savepoint class should not become a >>> public API, >>>>>>>>>> at least for now. What we need to discuss for the public API is >>> how the >>>>>>>>>> users can create or delete savepoints. For example, what the >>> table option >>>>>>>>>> looks like, what commands and options are provided for the Flink >>> action, >>>>>>>>>> etc. >>>>>>>>>> >>>>>>>>>> 2. Currently most Flink actions are related to streaming >>> processing, so >>>>>>>>>> only Flink can support them. However, savepoint creation and >>> deletion seems >>>>>>>>>> like a feature for batch processing. So aside from Flink actions, >>> shall we >>>>>>>>>> also provide something like Spark actions for savepoints? >>>>>>>>>> >>>>>>>>>> I would also like to comment on Shammon's views. >>>>>>>>>> >>>>>>>>>> Should we introduce an option for savepoint path which may be >>> different >>>>>>>>>>> from 'warehouse'? Then users can backup the data of savepoint. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> I don't see this is necessary. To backup a table the user just >>> need to copy >>>>>>>>>> all files from the table directory. Savepoint in Paimon, as far >>> as I >>>>>>>>>> understand, is mainly for users to review historical data, not >>> for backing >>>>>>>>>> up tables. >>>>>>>>>> >>>>>>>>>> Will the savepoint copy data files from snapshot or only save >>> meta files? >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> It would be a heavy burden if a savepoint copies all its files. >>> As I >>>>>>>>>> mentioned above, savepoint is not for backing up tables. >>>>>>>>>> >>>>>>>>>> How can users create a new table and restore data from the >>> specified >>>>>>>>>>> savepoint? >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> This reminds me of savepoints in Flink. Still, savepoint is not >>> for backing >>>>>>>>>> up tables so I guess we don't need to support "restoring data" >>> from a >>>>>>>>>> savepoint. >>>>>>>>>> >>>>>>>>>> Shammon FY <[email protected]> 于2023年5月17日周三 10:32写道： >>>>>>>>>> >>>>>>>>>>> Thanks Zelin for initiating this discussion. I have some >>> comments: >>>>>>>>>>> >>>>>>>>>>> 1. Should we introduce an option for savepoint path which may be >>>>>>>>>> different >>>>>>>>>>> from 'warehouse'? Then users can backup the data of savepoint. >>>>>>>>>>> >>>>>>>>>>> 2. Will the savepoint copy data files from snapshot or only save >>> meta >>>>>>>>>>> files? The description in the PIP "After we introduce savepoint, >>> we >>>>>>>>>> should >>>>>>>>>>> also check if the data files are used by savepoints." looks like >>> we only >>>>>>>>>>> save meta files for savepoint. >>>>>>>>>>> >>>>>>>>>>> 3. How can users create a new table and restore data from the >>> specified >>>>>>>>>>> savepoint? >>>>>>>>>>> >>>>>>>>>>> Best, >>>>>>>>>>> Shammon FY >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> On Wed, May 17, 2023 at 10:19 AM Jingsong Li < >>> [email protected]> >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> Thanks Zelin for driving. >>>>>>>>>>>> >>>>>>>>>>>> Some comments: >>>>>>>>>>>> >>>>>>>>>>>> 1. I think it's possible to advance `Proposed Changes` to the >>> top, >>>>>>>>>>>> Public API has no meaning if I don't know how to do it. >>>>>>>>>>>> >>>>>>>>>>>> 2. Public API, Savepoint and SavepointManager are not Public >>> API, only >>>>>>>>>>>> Flink action or configuration option should be public API. >>>>>>>>>>>> >>>>>>>>>>>> 3.Maybe we can have a separate chapter to describe >>>>>>>>>>>> `savepoint.create-interval`, maybe 'Periodically savepoint'? It >>> is not >>>>>>>>>>>> just an interval, because the true user case is savepoint after >>> 0:00. >>>>>>>>>>>> >>>>>>>>>>>> 4.About 'Interaction with Snapshot', to be continued ... >>>>>>>>>>>> >>>>>>>>>>>> Best, >>>>>>>>>>>> Jingsong >>>>>>>>>>>> >>>>>>>>>>>> On Tue, May 16, 2023 at 7:07 PM yu zelin <[email protected] >>>> >>>>>>>>>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> Hi, Paimon Devs, >>>>>>>>>>>>> I’d like to start a discussion about PIP-4[1]. In this >>> PIP, I >>>>>>>>>> want >>>>>>>>>>>> to talk about why we need savepoint, and some thoughts about >>> managing >>>>>>>>>> and >>>>>>>>>>>> using savepoint. Look forward to your question and suggestions. >>>>>>>>>>>>> >>>>>>>>>>>>> Best, >>>>>>>>>>>>> Yu Zelin >>>>>>>>>>>>> >>>>>>>>>>>>> [1] https://cwiki.apache.org/confluence/x/NxE0Dw >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> >>>>>>>> >>>> >>> >
