[8.x] Store arrays offsets for keyword fields natively with synthetic source #122997
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… source Backporting elastic#113757 to 8.x branch. The keyword doc values field gets an extra sorted doc values field, that encodes the order of how array values were specified at index time. This also captures duplicate values. This is stored in an offset to ordinal array that gets zigzag vint encoded into a sorted doc values field. For example, in case of the following string array for a keyword field: ["c", "b", "a", "c"]. Sorted set doc values: ["a", "b", "c"] with ordinals: 0, 1 and 2. The offset array will be: [2, 1, 0, 2] Null values are also supported. For example ["c", "b", null, "c"] results into sorted set doc values: ["b", "c"] with ordinals: 0 and 1. The offset array will be: [1, 0, -1, 1] Empty arrays are also supported by encoding a zigzag vint array of zero elements. Limitations: currently only doc values based array support for keyword field mapper. multi level leaf arrays are flattened. For example: [[b], [c]] -> [b, c] arrays are always synthesized as one type. In case of keyword field, [1, 2] gets synthesized as ["1", "2"]. These limitations can be addressed, but some require more complexity and or additional storage. With this PR, keyword field array will no longer be stored in ignored source, but array offsets are kept track of in an adjacent sorted doc value field. This only applies if index.mapping.synthetic_source_keep is set to arrays (default for logsdb).
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…hetic source Update index version check after elastic#122997 backport was merged.
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Backporting #113757 to 8.x branch.
The keyword doc values field gets an extra sorted doc values field, that encodes the order of how array values were specified at index time. This also captures duplicate values. This is stored in an offset to ordinal array that gets zigzag vint encoded into a sorted doc values field.
For example, in case of the following string array for a keyword field: ["c", "b", "a", "c"].
Sorted set doc values: ["a", "b", "c"] with ordinals: 0, 1 and 2. The offset array will be: [2, 1, 0, 2]
Null values are also supported. For example ["c", "b", null, "c"] results into sorted set doc values: ["b", "c"] with ordinals: 0 and 1. The offset array will be: [1, 0, -1, 1]
Empty arrays are also supported by encoding a zigzag vint array of zero elements.
Limitations:
currently only doc values based array support for keyword field mapper. multi level leaf arrays are flattened. For example: [[b], [c]] -> [b, c] arrays are always synthesized as one type. In case of keyword field, [1, 2] gets synthesized as ["1", "2"]. These limitations can be addressed, but some require more complexity and or additional storage.
With this PR, keyword field array will no longer be stored in ignored source, but array offsets are kept track of in an adjacent sorted doc value field. This only applies if index.mapping.synthetic_source_keep is set to arrays (default for logsdb).