emkornfield commented on code in PR #11238: URL: https://github.com/apache/iceberg/pull/11238#discussion_r1801477641
########## format/puffin-spec.md: ########## @@ -123,6 +123,49 @@ The blob metadata for this blob may include following properties: - `ndv`: estimate of number of distinct values, derived from the sketch. +#### `delete-vector-v1` blob type + +A serialized delete vector (bitmap) that represents the positions of rows in a +file that are deleted. A set bit at position P indicates that the row at +position P is deleted. + +The vector supports positive 64-bit positions, but is optimized for cases where +most positions fit in 32 bits by using a collection of 32-bit Roaring bitmaps. +64-bit positions are divided into a 32-bit "key" using the most significant 4 +bytes and a 32-bit sub-position using the least significant 4 bytes. For each +key in the set of positions, a 32-bit Roaring bitmap is maintained to store a +set of 32-bit sub-positions for that key. + +To test whether a certain position is set, its most significant 4 bytes (the +key) are used to find a 32-bit bitmap and the least significant 4 bytes (the +sub-position) are tested for inclusion in the bitmap. If a bitmap is not found +for the key, then it is not set. + +The serialized blob contains: +* The length of the vector and magic bytes stored as 4 bytes, little-endian Review Comment: > The main use case for maintaining compatibility with the Delta format is that it's hard to move old jobs to new code. We see a similar issue in Hive to Iceberg migrations, too, where unknown older readers prevent migration because they are hard to track down and often read files directly from the backing object store. I'd like to avoid the same problem here, where all readers need to be identified and migrated at the same time. Doing that requires temporarily producing Delta metadata, which this makes possible. This will already be the case for an upgrade to Iceberg V3, where as currently proposed all position delete files will be migrated to DV? Is it technically harder to do a similar migration of Delta lake to a new version if users would want to interop with Iceberg? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
