I think Apache Paimon could point us in the direction of supporting streaming upserts use cases. We are already working on some of the building blocks like deletion vectors and Flink compaction.
+1 to the proposal since users are not recommended to use equality deletes for streaming upserts anyway. [1] https://medium.com/@ipolyzos_/apache-paimon-introducing-deletion-vectors-584666ee90de On Thu, Oct 31, 2024 at 10:16 AM Ajantha Bhat <ajanthab...@gmail.com> wrote: > Equality deletes aren't only written from Flink; Iceberg Kafka Connect > (Tabular’s version) also writes equality deletes for upserts. > > Writers write out reference to what values are deleted (in a partition or >> globally). There can be an unlimited number of equality deletes and they >> all must be checked for every data file that is read. The cost of >> determining deleted rows is essentially given to the reader > > > Should we focus on optimizing these by compacting them into a single file > to reduce read overhead? > What are the plans for supporting streaming writes in Iceberg if we move > away from equality deletes? Can we achieve real-time writing with position > deletes instead, or would this impact write performance? > > - Ajantha > > On Thu, Oct 31, 2024 at 7:18 AM Gang Wu <ust...@gmail.com> wrote: > >> Thanks Russell for bringing this up! >> >> +1 on deprecating equality deletes. >> >> IMHO, this is something that should reside only in the ingestion engine. >> >> Best, >> Gang >> >> On Thu, Oct 31, 2024 at 5:07 AM Russell Spitzer < >> russell.spit...@gmail.com> wrote: >> >>> Background: >>> >>> 1) Position Deletes >>> >>> >>> Writers determine what rows are deleted and mark them in a 1 for 1 >>> representation. With delete vectors this means every data file has at most >>> 1 delete vector that it is read in conjunction with to excise deleted rows. >>> Reader overhead is more or less constant and is very predictable. >>> >>> >>> The main cost of this mode is that deletes must be determined at write >>> time which is expensive and can be more difficult for conflict resolution >>> >>> 2) Equality Deletes >>> >>> Writers write out reference to what values are deleted (in a partition >>> or globally). There can be an unlimited number of equality deletes and they >>> all must be checked for every data file that is read. The cost of >>> determining deleted rows is essentially given to the reader. >>> >>> Conflicts almost never happen since data files are not actually changed >>> and there is almost no cost to the writer to generate these. Almost all >>> costs related to equality deletes are passed on to the reader. >>> >>> Proposal: >>> >>> Equality deletes are, in my opinion, unsustainable and we should work on >>> deprecating and removing them from the specification. At this time, I know >>> of only one engine (Apache Flink) which produces these deletes but almost >>> all engines have implementations to read them. The cost of implementing >>> equality deletes on the read path is difficult and unpredictable in terms >>> of memory usage and compute complexity. We’ve had suggestions of >>> implementing rocksdb inorder to handle ever growing sets of equality >>> deletes which in my opinion shows that we are going down the wrong path. >>> >>> Outside of performance, Equality deletes are also difficult to use in >>> conjunction with many other features. For example, any features requiring >>> CDC or Row lineage are basically impossible when equality deletes are in >>> use. When Equality deletes are present, the state of the table can only be >>> determined with a full scan making it difficult to update differential >>> structures. This means materialized views or indexes need to essentially be >>> fully rebuilt whenever an equality delete is added to the table. >>> >>> Equality deletes essentially remove complexity from the write side but >>> then add what I believe is an unacceptable level of complexity to the read >>> side. >>> >>> Because of this I suggest we deprecate Equality Deletes in V3 and slate >>> them for full removal from the Iceberg Spec in V4. >>> >>> I know this is a big change and compatibility breakage so I would like >>> to introduce this idea to the community and solicit feedback from all >>> stakeholders. I am very flexible on this issue and would like to hear the >>> best issues both for and against removal of Equality Deletes. >>> >>> Thanks everyone for your time, >>> >>> Russ Spitzer >>> >>>
