178 lines
8.4 KiB
Markdown
178 lines
8.4 KiB
Markdown
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# ZAP File Format
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## Legend
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### Sections
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|========|
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| | section
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|========|
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### Fixed-size fields
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|--------| |----| |--| |-|
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| | uint64 | | uint32 | | uint16 | | uint8
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|--------| |----| |--| |-|
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### Varints
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|~~~~~~~~|
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| | varint(up to uint64)
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|~~~~~~~~|
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### Arbitrary-length fields
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|--------...---|
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| | arbitrary-length field (string, vellum, roaring bitmap)
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|--------...---|
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### Chunked data
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[--------]
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[ ]
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[--------]
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## Overview
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Footer section describes the configuration of particular ZAP file. The format of footer is version-dependent, so it is necessary to check `V` field before the parsing.
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|==================================================|
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| Stored Fields |
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|==================================================|
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|-----> | Stored Fields Index |
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| |==================================================|
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| | Dictionaries + Postings + DocValues |
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| |==================================================|
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| |---> | DocValues Index |
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| | |==================================================|
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| | | Fields |
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| | |==================================================|
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| | |-> | Fields Index |
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| | | |========|========|========|========|====|====|====|
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| | | | D# | SF | F | FDV | CF | V | CC | (Footer)
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| | | |========|====|===|====|===|====|===|====|====|====|
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|-+-+-----------------| | |
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| |--------------------------| |
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|-------------------------------------|
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D#. Number of Docs.
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SF. Stored Fields Index Offset.
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F. Field Index Offset.
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FDV. Field DocValue Offset.
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CF. Chunk Factor.
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V. Version.
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CC. CRC32.
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## Stored Fields
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Stored Fields Index is `D#` consecutive 64-bit unsigned integers - offsets, where relevant Stored Fields Data records are located.
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0 [SF] [SF + D# * 8]
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| Stored Fields | Stored Fields Index |
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|================================|==================================|
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| | |
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| |--------------------| ||--------|--------|. . .|--------||
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| |-> | Stored Fields Data | || 0 | 1 | | D# - 1 ||
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| | |--------------------| ||--------|----|---|. . .|--------||
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|===|============================|==============|===================|
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|-------------------------------------------|
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Stored Fields Data is an arbitrary size record, which consists of metadata and [Snappy](https://github.com/golang/snappy)-compressed data.
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Stored Fields Data
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|~~~~~~~~|~~~~~~~~|~~~~~~~~...~~~~~~~~|~~~~~~~~...~~~~~~~~|
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| MDS | CDS | MD | CD |
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|~~~~~~~~|~~~~~~~~|~~~~~~~~...~~~~~~~~|~~~~~~~~...~~~~~~~~|
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MDS. Metadata size.
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CDS. Compressed data size.
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MD. Metadata.
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CD. Snappy-compressed data.
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## Fields
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Fields Index section located between addresses `F` and `len(file) - len(footer)` and consist of `uint64` values (`F1`, `F2`, ...) which are offsets to records in Fields section. We have `F# = (len(file) - len(footer) - F) / sizeof(uint64)` fields.
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(...) [F] [F + F#]
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| Fields | Fields Index. |
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|================================|================================|
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| |~~~~~~~~|~~~~~~~~|---...---|||--------|--------|...|--------||
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||->| Dict | Length | Name ||| 0 | 1 | | F# - 1 ||
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|| |~~~~~~~~|~~~~~~~~|---...---|||--------|----|---|...|--------||
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||===============================|==============|=================|
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|----------------------------------------------|
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## Dictionaries + Postings
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Each of fields has its own dictionary, encoded in [Vellum](https://github.com/couchbase/vellum) format. Dictionary consists of pairs `(term, offset)`, where `offset` indicates the position of postings (list of documents) for this particular term.
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|================================================================|- Dictionaries +
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| | Postings +
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| | DocValues
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| Freq/Norm (chunked) |
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| [~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~] |
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| |->[ Freq | Norm (float32 under varint) ] |
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| | [~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~] |
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| |------------------------------------------------------------| |
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| Location Details (chunked) | |
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| [~~~~~~|~~~~~|~~~~~~~|~~~~~|~~~~~~|~~~~~~~~|~~~~~] | |
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| |->[ Size | Pos | Start | End | Arr# | ArrPos | ... ] | |
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| | [~~~~~~|~~~~~|~~~~~~~|~~~~~|~~~~~~|~~~~~~~~|~~~~~] | |
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| |----------------------| | |
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| Postings List | | |
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| |~~~~~~~~|~~~~~|~~|~~~~~~~~|-----------...--| | |
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| |->| F/N | LD | Length | ROARING BITMAP | | |
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| | |~~~~~|~~|~~~~~~~~|~~~~~~~~|-----------...--| | |
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| | |----------------------------------------------| |
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| |--------------------------------------| |
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| Dictionary | |
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| |~~~~~~~~|--------------------------|-...-| |
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| |->| Length | VELLUM DATA : (TERM -> OFFSET) | |
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| | |~~~~~~~~|----------------------------...-| |
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|======|=========================================================|- DocValues Index
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|======|=========================================================|- Fields
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| |~~~~|~~~|~~~~~~~~|---...---| |
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| | Dict | Length | Name | |
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| |~~~~~~~~|~~~~~~~~|---...---| |
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|================================================================|
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## DocValues
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DocValues Index is `F#` pairs of varints, one pair per field. Each pair of varints indicates start and end point of DocValues slice.
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|================================================================|
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| |------...--| |
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| |->| DocValues |<-| |
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| | |------...--| | |
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|==|=================|===========================================|- DocValues Index
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||~|~~~~~~~~~|~~~~~~~|~~| |~~~~~~~~~~~~~~|~~~~~~~~~~~~||
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|| DV1 START | DV1 STOP | . . . . . | DV(F#) START | DV(F#) END ||
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||~~~~~~~~~~~|~~~~~~~~~~| |~~~~~~~~~~~~~~|~~~~~~~~~~~~||
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|================================================================|
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DocValues is chunked Snappy-compressed values for each document and field.
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[~~~~~~~~~~~~~~~|~~~~~~|~~~~~~~~~|-...-|~~~~~~|~~~~~~~~~|--------------------...-]
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[ Doc# in Chunk | Doc1 | Offset1 | ... | DocN | OffsetN | SNAPPY COMPRESSED DATA ]
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[~~~~~~~~~~~~~~~|~~~~~~|~~~~~~~~~|-...-|~~~~~~|~~~~~~~~~|--------------------...-]
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Last 16 bytes are description of chunks.
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|~~~~~~~~~~~~...~|----------------|----------------|
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| Chunk Sizes | Chunk Size Arr | Chunk# |
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|~~~~~~~~~~~~...~|----------------|----------------|
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