1. State TTL for Value Columns > I’m planning on adding this, and we may collaborate on it in the future.
+1 on this, just ping me. 2. Metadata Table vs. Metadata Column After some code digging and POC all I can say that with heavy effort we can maybe add such changes that we're able to show metadata of a savepoint from catalog. I'm not against that but from user perspective this has limited value, let me explain why. >From high level perspective I see the following which I see agreement on: * We should have a catalog which is representing one or more jobs savepoint data set (future plan) * Savepoints should be able to be registered in the catalog which are then databases (future plan) * There must be a possiblity to create tables from databases where users can read state data (exists already) In terms of metadata, If I understand correctly then the suggested approach would be to access it from the catalog describe command, right? Adding that info when specific database describe command is executed could be done. The question is for instance how can users create such a logic that tells them what is the difference between multiple savepoints? Just to give some examples: * per operator size changes between savepoints * show values from operator data where state size reaches a boundary * in general "find which checkpoint ruined things" is quite common pattern What I would like to highlight here is that from Flink point of view the metadata can be considered as a static side output information but for users these values are actual real data where logic is planned to build around. > The metadata is more like one-time information instead of a streaming data that changes all the time, so a single connector seems to be an overkill. State data is also static within a savepoint and that's the reason why the state processor API is working in batch mode. When we handle multiple checkpoints in a streaming fashion then this can be viewed from another angle. We can come up with more lightweight solution other than a new connector but enforcing users to parse the catalog describe command output in order to compare multiple savepoints doesn't sound smooth user experience. Honestly I've no other idea how exposing metadata as real user data so waiting on other approaches. BR, G On Thu, Mar 13, 2025 at 2:44 AM Shengkai Fang <fskm...@gmail.com> wrote: > Looking forward to hearing the good news! > > Best, > Shengkai > > Gabor Somogyi <gabor.g.somo...@gmail.com> 于2025年3月12日周三 22:24写道： > > > Thanks for both the valuable input! > > > > Let me take a closer look at the suggestions, like the Catalog > capabilities > > and possibility of embedding TypeInformation or > > StateDescriptor metadata directly into the raw state files... > > > > BR, > > G > > > > > > On Wed, Mar 12, 2025 at 8:17 AM Shengkai Fang <fskm...@gmail.com> wrote: > > > > > Thanks for Zakelly's clarification. > > > > > > 1. State TTL for Value Columns > > > > > > +1 to delay the discussion about this. > > > > > > 2. Metadata Table vs. Metadata Column > > > > > > I’d like to share my perspective on the State Catalog proposal. While > > > introducing this capability is beneficial, there is a blocker: the > > current > > > StateBackend architecture does not permit operators to encode > > > TypeInformation into the state—it only preserves the Serializer. This > > > limitation creates an asymmetry, as operators alone retain knowledge of > > the > > > data structure’s schema. > > > > > > To address this, I suggest allowing operators to embed TypeInformation > or > > > StateDescriptor metadata directly into the raw state files. Such a > design > > > would enable the Catalog to: > > > > > > 1. Parse state files and programmatically derive the schema and > > structural > > > guarantees for each state. > > > 2. Leverage existing Flink Table utilities, such as > > > LegacyTypeInfoDataTypeConverter (in > org.apache.flink.table.types.utils), > > to > > > bridge TypeInformation and DataType conversions. > > > > > > If we can not store the TypeInformation or StateDescriptor into the raw > > > state files, I am +1 for this FLIP to use metadata column to retrieve > > > information. > > > > > > Best, > > > Shengkai > > > > > > > > > > > > > > > Zakelly Lan <zakelly....@gmail.com> 于2025年3月12日周三 12:43写道： > > > > > > > Hi Gabor and Shengkai, > > > > > > > > Thanks for sharing your thoughts! This is a long discussion and sorry > > for > > > > the late reply (I'm busy catching up with release 2.0 these days). > > > > > > > > 1. State TTL for Value Columns > > > > > > > > > > > > Let me first clarify your thoughts to ensure I understand correctly. > > > IIUC, > > > > there is no persistent configuration for state TTL in the checkpoint. > > > While > > > > you can infer that TTL is enabled by reading the serializer, the > > > checkpoint > > > > itself only stores the last access time for each value. So the only > > thing > > > > we can show is the last access time for each value. But it is not > > > required > > > > for all state backends to store this, as they may directly store the > > > > expired time. This will also increase the difficulty of > implementation > > & > > > > maintenance. > > > > > > > > This once again reiterates the importance of unified metadata for > > > > checkpoints. I’m planning on adding this, and we may collaborate on > it > > in > > > > the future. > > > > > > > > 2. Metadata Table vs. Metadata Column > > > > > > > > > > > > I'm not in favor of adding a new connector for metadata. The metadata > > is > > > > more like one-time information instead of a streaming data that > changes > > > all > > > > the time, so a single connector seems to be an overkill. It is not > easy > > > to > > > > withdraw a connector if we have a better solution in future. I'm not > > > > familiar with current Catalog capabilities, and if it could extract > and > > > > show some operator-level information from savepoint, that would be > > great. > > > > > > > > If the Catalog can't do that, I would consider the current FLIP to > be a > > > > compromise solution. > > > > > > > > And if we have that unified metadata for checkpoint/savepoint in > > future, > > > we > > > > may directly register savepoint in catalog, and create a source > without > > > > specifying complex columns, as well as describe the savepoint catalog > > to > > > > get the metadata. That's a good solution in my mind. > > > > > > > > > > > > Best, > > > > Zakelly > > > > > > > > On Wed, Mar 12, 2025 at 10:35 AM Shengkai Fang <fskm...@gmail.com> > > > wrote: > > > > > > > > > Hi Gabor, > > > > > > > > > > > 2. Adding a new connector with `savepoint-metadata` > > > > > > > > > > I would argue against introducing a new connector type named > > > > > savepoint-metadata, as the existing Catalog mechanism can > inherently > > > > > provide the necessary connector factory capabilities. I’ve detailed > > > this > > > > > proposal in branch[1]. Please take a moment to review it. > > > > > > > > > > If we introduce a connector named `savepoint-metadata`, it means > user > > > can > > > > > create a temporary table with connector `savepoint-metadata` and > the > > > > > connector needs to check whether table schema is same to the schema > > we > > > > > proposed in the FLIP. On the other hand, it's not easy work for > > others > > > to > > > > > users a metadata table with same schema. > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > https://github.com/apache/flink/compare/master...fsk119:flink:state-metadata?expand=1#diff-712a7bc92fe46c405fb0e61b475bb2a005cb7a72bab7df28bbb92744bcb5f465R63 > > > > > > > > > > Best, > > > > > Shengkai > > > > > > > > > > Gabor Somogyi <gabor.g.somo...@gmail.com> 于2025年3月11日周二 16:56写道： > > > > > > > > > > > Hi Shengkai, > > > > > > > > > > > > > 1. State TTL for Value Columns > > > > > > > > > > > > From directional perspective I agree your idea how it can be > > > > implemented. > > > > > > Previously I've mentioned that TTL information is not exposed on > > the > > > > > state > > > > > > processor API (which the SQL state connector uses to read data) > > > > > > and unless somebody show me the opposite this FLIP is not going > to > > > > > address > > > > > > this to avoid feature creep. Our users are also interested in TTL > > so > > > > > > sooner or later we're going to expose it, this is matter of > > > scheduling. > > > > > > > > > > > > > 2. Adding a new connector with `savepoint-metadata` > > > > > > > > > > > > Not sure I understand your point at all related StateCatalog. > First > > > of > > > > > all > > > > > > I can't agree more that StateCatalog is needed and is a planned > > > > building > > > > > > block in an upcoming > > > > > > FLIP but not sure how can it help now? No matter what, your > > knowledge > > > > is > > > > > > essential when we add StateCatalog. Let me expose my > understanding > > in > > > > > this > > > > > > area: > > > > > > * First we need create table statements to access state data and > > > > metadata > > > > > > * When we have that then we can add StateCatalog which could > > > > potentially > > > > > > ease the life of users by for ex. giving off-the-shelf tables > > without > > > > > > sweating with create table statements > > > > > > > > > > > > User expectations: > > > > > > * See state data (this is fulfilled with the existing connector) > > > > > > * See metadata about state data like TTL (this can be added as > > > metadata > > > > > > column as you suggested since it belongs to the data) > > > > > > * See metadata about operators (this can be added from > > > > > savepoint-metadata) > > > > > > > > > > > > Important to highlight that state data table format differs from > > > state > > > > > > metadata table format. Namely one table has rows for state values > > and > > > > > > another has rows for operators, right? > > > > > > I think that's the reason why you've pinpointed out that the > > > suggested > > > > > > metadata columns are somewhat clunky. > > > > > > > > > > > > As a conclusion I agree to add ${state-name}_ttl metadata column > > > later > > > > on > > > > > > since it belongs to the state value and adding a new table type > > (like > > > > you > > > > > > suggested similar to PG [1]) > > > > > > for metadata. Please see how Spark does that too [2]. > > > > > > > > > > > > If you have better approach then please elaborate with more > details > > > and > > > > > > help me to understand your point. > > > > > > > > > > > > > Up until now we've seen even in TB savepoints that the number > of > > > keys > > > > > can > > > > > > > be extremely huge but not the per key state itself. > > > > > > > But again, this is a good feature as-is and can be handled in a > > > > > separate > > > > > > > jira. > > > > > > > > > > > > I've just created > > https://issues.apache.org/jira/browse/FLINK-37456. > > > > > > > > > > > > [1] https://www.postgresql.org/docs/current/view-pg-tables.html > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > https://www.databricks.com/blog/announcing-state-reader-api-new-statestore-data-source > > > > > > > > > > > > BR, > > > > > > G > > > > > > > > > > > > > > > > > > On Tue, Mar 11, 2025 at 3:55 AM Shengkai Fang <fskm...@gmail.com > > > > > > wrote: > > > > > > > > > > > > > Hi, Gabor. Thanks for your response. > > > > > > > > > > > > > > > 1. State TTL for Value Columns > > > > > > > > > > > > > > Thank you for addressing the limitations here. However, I > believe > > > it > > > > > > would > > > > > > > be beneficial to further clarify the API in this FLIP regarding > > how > > > > > users > > > > > > > can specify the TTL column. > > > > > > > > > > > > > > One potential approach that comes to mind is using a > standardized > > > > > naming > > > > > > > convention such as ${state-name}_ttl for the metadata column > that > > > > > defines > > > > > > > the TTL value. In terms of implementation, the > > listReadableMetadata > > > > > > > function could: > > > > > > > > > > > > > > 1. Read the table’s columns and configuration, > > > > > > > 2. Extract all defined state names, and > > > > > > > 3. Return a structured list of metadata entries formatted as > > > > > > > ${state-name}_ttl. > > > > > > > > > > > > > > WDYT? > > > > > > > > > > > > > > > 2. Adding a new connector with `savepoint-metadata` > > > > > > > > > > > > > > Introducing a new connector type at this stage may > unnecessarily > > > > > > complicate > > > > > > > the system. Given that every table already belongs to a > Catalog, > > > > which > > > > > is > > > > > > > designed to provide a Factory for building source or sink > > > > connectors, I > > > > > > > propose integrating a dedicated StateCatalog instead. This > > approach > > > > > would > > > > > > > allow us to: > > > > > > > > > > > > > > 1. Leverage the Catalog’s existing capabilities to manage TTL > > > > metadata > > > > > > > (e.g., state names and TTL logic) without duplicating > > > functionality. > > > > > > > 2. Provide a unified interface for connector instantiation and > > > > metadata > > > > > > > handling through the Catalog’s Factory pattern. > > > > > > > > > > > > > > Would this design decision better align with our architecture’s > > > > > > > extensibility and reduce redundancy? > > > > > > > > > > > > > > > Up until now we've seen even in TB savepoints that the number > > of > > > > keys > > > > > > can > > > > > > > > be extremely huge but not the per key state itself. > > > > > > > > But again, this is a good feature as-is and can be handled > in a > > > > > > separate > > > > > > > > jira. > > > > > > > > > > > > > > +1 for a separate jira. > > > > > > > > > > > > > > Best, > > > > > > > Shengkai > > > > > > > > > > > > > > Gabor Somogyi <gabor.g.somo...@gmail.com> 于2025年3月10日周一 > 19:05写道： > > > > > > > > > > > > > > > Hi Shengkai, > > > > > > > > > > > > > > > > Please see my comments inline. > > > > > > > > > > > > > > > > BR, > > > > > > > > G > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Mar 3, 2025 at 7:07 AM Shengkai Fang < > > fskm...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi, Gabor. Thanks for your the FLIP. I have some questions > > > about > > > > > the > > > > > > > > FLIP: > > > > > > > > > > > > > > > > > > 1. State TTL for Value Columns > > > > > > > > > How can users retrieve the state TTL (Time-to-Live) for > each > > > > value > > > > > > > > column? > > > > > > > > > From my understanding of the current design, it seems that > > this > > > > > > > > > functionality is not supported. Could you clarify if there > > are > > > > > plans > > > > > > to > > > > > > > > > address this limitation? > > > > > > > > > > > > > > > > > > > > > > > > > Since the state processor API is not yet exposing this > > > information > > > > > this > > > > > > > > would require several steps. > > > > > > > > First, the state processor API support needs to be added > which > > > can > > > > be > > > > > > > then > > > > > > > > exposed on the SQL API. > > > > > > > > This is definitely a future improvement which is useful and > can > > > be > > > > > > > handled > > > > > > > > in a separate jira. > > > > > > > > > > > > > > > > > > > > > > > > > 2. Metadata Table vs. Metadata Column > > > > > > > > > The metadata information described in the FLIP appears to > be > > > > > intended > > > > > > > to > > > > > > > > > describe the state files stored at a specific location. To > > me, > > > > this > > > > > > > > concept > > > > > > > > > aligns more closely with system tables like pg_tables in > > > > PostgreSQL > > > > > > [1] > > > > > > > > or > > > > > > > > > the INFORMATION_SCHEMA in MySQL [2]. > > > > > > > > > > > > > > > > > > > > > > > > > Adding a new connector with `savepoint-metadata` is a > > possibility > > > > > where > > > > > > > we > > > > > > > > can create such functionality. > > > > > > > > I'm not against that, just want to have a common agreement > that > > > we > > > > > > would > > > > > > > > like to move that direction. > > > > > > > > (As a side note not just PG but Spark also has similar > approach > > > > and I > > > > > > > > basically like the idea). > > > > > > > > If we would go that direction savepoint metadata can be > reached > > > in > > > > a > > > > > > way > > > > > > > > that one row would represent > > > > > > > > an operator with it's values something like this: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ┌─────────┬─────────┬─────────┬─────────┬─────────┬─────────┬─────────┬────────┐ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > │operatorN│operatorU│operatorH│paralleli│maxParall│subtaskSt│coordinat│totalSta│ > > > > > > > > │ame │id │ash │sm │elism > > > > > > > > │atesCount│orStateSi│tesSizeI│ > > > > > > > > │ │ │ │ │ │ > > > > > > > > │zeInBytes│nBytes │ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ├─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼────────┤ > > > > > > > > │Source: │datagen-s│47aee9439│2 │128 │2 > │16 > > > > > > > > │546 │ > > > > > > > > │datagen-s│ource-uid│4d6ea26e2│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │ource │ │d544bef0a│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │ │ │37bb5 │ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ├─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼────────┤ > > > > > > > > │long-udf-│long-udf-│6ed3f40bf│2 │128 │2 > │0 > > > > > > │0 > > > > > > > > │ > > > > > > > > │with-mast│with-mast│f3c8dfcdf│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │er-hook │er-hook-u│cb95128a1│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │ │id │018f1 │ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ├─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼────────┤ > > > > > > > > │value-pro│value-pro│ca4f5fe9a│2 │128 │2 > │0 > > > > > > > > │40726 │ > > > > > > > > │cess │cess-uid │637b656f0│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │ │ │9ea78b3e7│ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > │ │ │a15b9 │ │ │ │ > > > > > │ > > > > > > > > │ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ├─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼────────┤ > > > > > > > > > > > > > > > > This table can then be joined with the actually existing > > > > `savepoint` > > > > > > > > connector created tables based on UID hash (which is unique > and > > > > > always > > > > > > > > exists). > > > > > > > > This would mean that the already existing table would need > > only a > > > > > > single > > > > > > > > metadata column which is the UID hash. > > > > > > > > WDYT? > > > > > > > > @zakelly, plz share your thoughts too. > > > > > > > > > > > > > > > > > > > > > > > > > If we opt to use metadata columns, every record in the > table > > > > would > > > > > > end > > > > > > > up > > > > > > > > > having identical values for these columns (please correct > me > > if > > > > I’m > > > > > > > > > mistaken). On the other hand, the state connector requires > > > users > > > > to > > > > > > > > specify > > > > > > > > > an operator UID or operator UID hash, after which it > outputs > > > > > > > user-defined > > > > > > > > > values in its records. This approach feels somewhat > redundant > > > to > > > > > me. > > > > > > > > > > > > > > > > > > > > > > > > > If we would add a new `savepoint-metadata` connector then > this > > > can > > > > be > > > > > > > > addressed. > > > > > > > > On the other hand UID and UID hash are having either-or > > > > relationship > > > > > > from > > > > > > > > config perspective, > > > > > > > > so when a user provides the UID then he/she can be interested > > in > > > > the > > > > > > hash > > > > > > > > for further calculations > > > > > > > > (the whole Flink internals are depending on the hash). > Printing > > > out > > > > > the > > > > > > > > human readable UID > > > > > > > > is an explicit requirement from the user side because hashes > > are > > > > not > > > > > > > human > > > > > > > > readable. > > > > > > > > > > > > > > > > > > > > > > > > > 3. Handling LIST and MAP States in the State Connector > > > > > > > > > I have concerns about how the current design handles LIST > and > > > MAP > > > > > > > states. > > > > > > > > > Specifically, the state connector uses Flink SQL’s MAP and > > > ARRAY > > > > > > types, > > > > > > > > > which implies that it attempts to load entire MAP or LIST > > > states > > > > > into > > > > > > > > > memory. > > > > > > > > > > > > > > > > > > However, in many real-world scenarios, these states can > grow > > > very > > > > > > > large. > > > > > > > > > Typically, the state API addresses this by providing an > > > iterator > > > > to > > > > > > > > > traverse elements within the state incrementally. I’m > unsure > > > > > whether > > > > > > > I’ve > > > > > > > > > missed something in FLIP-496 or FLIP-512, but it seems that > > the > > > > > > current > > > > > > > > > design might struggle with scalability in such cases. > > > > > > > > > > > > > > > > > > > > > > > > > You see it good, the current implementation keeps state for a > > > > single > > > > > > key > > > > > > > in > > > > > > > > memory. > > > > > > > > Back in the days we've considered this potential issue and > > > > concluded > > > > > > that > > > > > > > > this is not necessarily > > > > > > > > needed for the initial version and can be done as a later > > > > > improvement. > > > > > > > > > > > > > > > > Up until now we've seen even in TB savepoints that the number > > of > > > > keys > > > > > > can > > > > > > > > be extremely huge but not the per key state itself. > > > > > > > > But again, this is a good feature as-is and can be handled > in a > > > > > > separate > > > > > > > > jira. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > Shengkai > > > > > > > > > > > > > > > > > > [1] > > > https://www.postgresql.org/docs/current/view-pg-tables.html > > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://dev.mysql.com/doc/refman/8.4/en/information-schema-tables-table.html > > > > > > > > > > > > > > > > > > Gabor Somogyi <gabor.g.somo...@gmail.com> 于2025年3月3日周一 > > > 02:00写道： > > > > > > > > > > > > > > > > > > > Hi Zakelly, > > > > > > > > > > > > > > > > > > > > In order to shoot for simplicity `METADATA VIRTUAL` as > key > > > > words > > > > > > for > > > > > > > > > > definition is the target. > > > > > > > > > > When it's not super complex the latter can be added too. > > > > > > > > > > > > > > > > > > > > BR, > > > > > > > > > > G > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sun, Mar 2, 2025 at 3:37 PM Zakelly Lan < > > > > > zakelly....@gmail.com> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Hi Gabor, > > > > > > > > > > > > > > > > > > > > > > +1 for this. > > > > > > > > > > > > > > > > > > > > > > Will the metadata column use `METADATA VIRTUAL` as key > > > words > > > > > for > > > > > > > > > > > definition, or `METADATA FROM xxx VIRTUAL` for > renaming, > > > just > > > > > > like > > > > > > > > the > > > > > > > > > > > Kafka table? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > > > Zakelly > > > > > > > > > > > > > > > > > > > > > > On Sat, Mar 1, 2025 at 1:31 PM Gabor Somogyi < > > > > > > > > > gabor.g.somo...@gmail.com> > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Hi All, > > > > > > > > > > > > > > > > > > > > > > > > I'd like to start a discussion of FLIP-512: Add meta > > > > > > information > > > > > > > to > > > > > > > > > SQL > > > > > > > > > > > > state connector [1]. > > > > > > > > > > > > Feel free to add your thoughts to make this feature > > > better. > > > > > > > > > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-512%3A+Add+meta+information+to+SQL+state+connector > > > > > > > > > > > > > > > > > > > > > > > > BR, > > > > > > > > > > > > G > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
