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gitea/vendor/github.com/blevesearch/zapx/v13/zap.md
Lauris BH f5abe2f563
Upgrade blevesearch dependency to v2.0.1 (#14346) 
* Upgrade blevesearch dependency to v2.0.1

* Update rupture to v1.0.0

* Fix test
2021-01-17 20:21:14 -05:00

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ZAP File Format

Legend

Sections

|========|
|        | section
|========|

Fixed-size fields

|--------|        |----|        |--|        |-|
|        | uint64 |    | uint32 |  | uint16 | | uint8
|--------|        |----|        |--|        |-|

Varints

|~~~~~~~~|
|        | varint(up to uint64)
|~~~~~~~~|

Arbitrary-length fields

|--------...---|
|              | arbitrary-length field (string, vellum, roaring bitmap)
|--------...---|

Chunked data

[--------]
[        ]
[--------]

Overview

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.

        |==================================================|
        | Stored Fields                                    |
        |==================================================|
|-----> | Stored Fields Index                              |
|       |==================================================|   
|       | Dictionaries + Postings + DocValues              | 
|       |==================================================|
| |---> | DocValues Index                                  |
| |     |==================================================|   
| |     | Fields                                           |
| |     |==================================================|
| | |-> | Fields Index                                     |
| | |   |========|========|========|========|====|====|====|
| | |   |     D# |     SF |      F |    FDV | CF |  V | CC | (Footer)
| | |   |========|====|===|====|===|====|===|====|====|====|
| | |                 |        |        |
|-+-+-----------------|        |        |
  | |--------------------------|        |
  |-------------------------------------|

 D#. Number of Docs.
 SF. Stored Fields Index Offset.
  F. Field Index Offset.
FDV. Field DocValue Offset.
 CF. Chunk Factor.
  V. Version.
 CC. CRC32.

Stored Fields

Stored Fields Index is D# consecutive 64-bit unsigned integers - offsets, where relevant Stored Fields Data records are located.

0                                [SF]                   [SF + D# * 8]
| Stored Fields                  | Stored Fields Index              |
|================================|==================================|
|                                |                                  |
|       |--------------------|   ||--------|--------|. . .|--------||
|   |-> | Stored Fields Data |   ||      0 |      1 |     | D# - 1 ||
|   |   |--------------------|   ||--------|----|---|. . .|--------||
|   |                            |              |                   |
|===|============================|==============|===================|
    |                                           |
    |-------------------------------------------|

Stored Fields Data is an arbitrary size record, which consists of metadata and Snappy-compressed data.

Stored Fields Data
|~~~~~~~~|~~~~~~~~|~~~~~~~~...~~~~~~~~|~~~~~~~~...~~~~~~~~|
|    MDS |    CDS |                MD |                CD |
|~~~~~~~~|~~~~~~~~|~~~~~~~~...~~~~~~~~|~~~~~~~~...~~~~~~~~|

MDS. Metadata size.
CDS. Compressed data size.
MD. Metadata.
CD. Snappy-compressed data.

Fields

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.

(...)                            [F]                       [F + F#]
| Fields                         | Fields Index.                  |
|================================|================================|
|                                |                                |
|   |~~~~~~~~|~~~~~~~~|---...---|||--------|--------|...|--------||
||->|   Dict | Length |    Name |||      0 |      1 |   | F# - 1 ||
||  |~~~~~~~~|~~~~~~~~|---...---|||--------|----|---|...|--------||
||                               |              |                 |
||===============================|==============|=================|
 |                                              |
 |----------------------------------------------|

Dictionaries + Postings

Each of fields has its own dictionary, encoded in Vellum format. Dictionary consists of pairs (term, offset), where offset indicates the position of postings (list of documents) for this particular term.

|================================================================|- Dictionaries + 
|                                                                |   Postings +
|                                                                |    DocValues
|    Freq/Norm (chunked)                                         |
|    [~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~]                      |
| |->[ Freq | Norm (float32 under varint) ]                      |
| |  [~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~]                      |
| |                                                              |
| |------------------------------------------------------------| |
|    Location Details (chunked)                                | |
|    [~~~~~~|~~~~~|~~~~~~~|~~~~~|~~~~~~|~~~~~~~~|~~~~~]        | |
| |->[ Size | Pos | Start | End | Arr# | ArrPos | ... ]        | |
| |  [~~~~~~|~~~~~|~~~~~~~|~~~~~|~~~~~~|~~~~~~~~|~~~~~]        | |
| |                                                            | |
| |----------------------|                                     | |
|          Postings List |                                     | |
|         |~~~~~~~~|~~~~~|~~|~~~~~~~~|-----------...--|        | |
|      |->|    F/N |     LD | Length | ROARING BITMAP |        | |
|      |  |~~~~~|~~|~~~~~~~~|~~~~~~~~|-----------...--|        | |
|      |        |----------------------------------------------| |
|      |--------------------------------------|                  |
|          Dictionary                         |                  |
|         |~~~~~~~~|--------------------------|-...-|            |
|      |->| Length | VELLUM DATA : (TERM -> OFFSET) |            |
|      |  |~~~~~~~~|----------------------------...-|            |
|      |                                                         |
|======|=========================================================|- DocValues Index
|      |                                                         |
|======|=========================================================|- Fields
|      |                                                         |
| |~~~~|~~~|~~~~~~~~|---...---|                                  |
| |   Dict | Length |    Name |                                  |
| |~~~~~~~~|~~~~~~~~|---...---|                                  |
|                                                                |
|================================================================|

DocValues

DocValues Index is F# pairs of varints, one pair per field. Each pair of varints indicates start and end point of DocValues slice.

|================================================================|
|     |------...--|                                              |
|  |->| DocValues |<-|                                           |
|  |  |------...--|  |                                           |
|==|=================|===========================================|- DocValues Index
||~|~~~~~~~~~|~~~~~~~|~~|           |~~~~~~~~~~~~~~|~~~~~~~~~~~~||
|| DV1 START | DV1 STOP | . . . . . | DV(F#) START | DV(F#) END ||
||~~~~~~~~~~~|~~~~~~~~~~|           |~~~~~~~~~~~~~~|~~~~~~~~~~~~||
|================================================================|

DocValues is chunked Snappy-compressed values for each document and field.

[~~~~~~~~~~~~~~~|~~~~~~|~~~~~~~~~|-...-|~~~~~~|~~~~~~~~~|--------------------...-]
[ Doc# in Chunk | Doc1 | Offset1 | ... | DocN | OffsetN | SNAPPY COMPRESSED DATA ]
[~~~~~~~~~~~~~~~|~~~~~~|~~~~~~~~~|-...-|~~~~~~|~~~~~~~~~|--------------------...-]

Last 16 bytes are description of chunks.

|~~~~~~~~~~~~...~|----------------|----------------|
|   Chunk Sizes  | Chunk Size Arr |         Chunk# |
|~~~~~~~~~~~~...~|----------------|----------------|