emkornfield commented on code in PR #557: URL: https://github.com/apache/parquet-format/pull/557#discussion_r3353297986
########## Encodings.md: ########## @@ -391,3 +391,409 @@ After applying the transformation, the data has the following representation: ``` Bytes AA 00 A3 BB 11 B4 CC 22 C5 DD 33 D6 ``` + +<a name="ALP"></a> +### Adaptive Lossless floating-Point: (ALP = 10) + +Supported Types: FLOAT, DOUBLE + +This encoding is adapted from the paper +["ALP: Adaptive Lossless floating-Point Compression"](https://dl.acm.org/doi/10.1145/3626717) +by Afroozeh and Boncz (SIGMOD 2024). + +ALP works by converting floating-point values to integers using decimal scaling +(controlled by an *exponent* `e` and *factor* `f`), then applying Frame of +Reference (FOR) encoding and bit-packing. Values that cannot be losslessly +converted are stored separately as *exceptions*. The encoding achieves high +compression for decimal-like floating-point data (e.g., monetary values, sensor +readings) while remaining fully lossless. Each value is encoded independently, +enabling random access to individual values and parallel encode/decode. + +#### Overview + +ALP encoding consists of a page-level header followed by an offset array and one +or more encoded vectors (batches of values). Each vector contains up to +`vector_size` elements (default 1024). + +``` ++-------------+-----------------------------+--------------------------------------+ +| Header | Offset Array | Vector Data | +| (7 bytes) | (num_vectors * 4 bytes) | (variable) | ++-------------+------+------+-----+---------+----------+----------+-----+----------+ +| Page Header | off0 | off1 | ... | off N-1 | Vector 0 | Vector 1 | ... | Vec N-1 | +| (7 bytes) | (4B) | (4B) | | (4B) |(variable)|(variable)| |(variable)| ++-------------+------+------+-----+---------+----------+----------+-----+----------+ +``` + +The compression pipeline for each vector is: + +``` + Input: float/double array + | + v + +----------------------------------------------------------+ + | 1. CHOOSE PARAMETERS | + | Select (exponent, factor) pair for this vector | + +----------------------------------------------------------+ + | + v + +----------------------------------------------------------+ + | 2. DECIMAL ENCODING | + | encoded[i] = fast_round(value[i] * 10^e * 10^(-f)) | + | Detect exceptions where decode(encode(v)) != v | + +----------------------------------------------------------+ + | + v + +----------------------------------------------------------+ + | 3. FRAME OF REFERENCE (FOR) | + | min_val = min(encoded[]) | Review Comment: ```suggestion | min_val = min(encoded[:]) | ``` small nit show that it is meant to select all values, don't feel strongly. -- 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: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
