findepi commented on code in PR #11238: URL: https://github.com/apache/iceberg/pull/11238#discussion_r1799284820
########## 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: > So we will be specifically storing a "delta length" which is the real length - 4 bytes? But in manifests we will keep the full blob length including the crc bytes? That's... _concerning_ > Removing this would mean those checks can't be run and would also break compatibility with all older Delta readers. I wouldn't be worried about older Delta readers at all. - compatibility with Delta readers isn't a projec goal, is it? - compatibility with some old software that we have no control over, shouldn't be a project goal either? To be clear, it would be nice to reuse valuable concepts from Delta, but we don't need to replicate typos or design issues such as "length is length off by 4". -- 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
