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docs: add label offset table and postings offset table (#593) 

Signed-off-by: zhulongcheng <zhulongcheng.me@gmail.com>
This commit is contained in:
zhulongcheng 2019-05-03 04:23:58 +08:00 committed by Krasi Georgiev
parent 5512826f13
commit 3ccab17f5d
1 changed files with 34 additions and 10 deletions
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docs/format/index.md
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@ -153,7 +153,7 @@ For instance, a single label name with 4 different values will be encoded as:
└────┴───┴───┴──────────────┴──────────────┴──────────────┴──────────────┴───────┘
```
The sequence of label index sections is finalized by an [offset table](#offset-table) pointing to the beginning of each label index section for a given set of label names.
The sequence of label index sections is finalized by a [label offset table](#label-offset-table) containing label offset entries that points to the beginning of each label index section for a given label name.
### Postings
@ -175,24 +175,48 @@ Postings sections store monotonically increasing lists of series references that
└─────────────────────────────────────────┘
```
The sequence of postings sections is finalized by an [offset table](#offset-table) pointing to the beginning of each postings section for a given set of label names.
The sequence of postings sections is finalized by a [postings offset table](#postings-offset-table) containing postings offset entries that points to the beginning of each postings section for a given label pair.
### Offset Table
### Label Offset Table
An offset table stores a sequence of entries that maps a list of strings to an offset. They are used to track label index and postings sections. They are read into memory when an index file is loaded.
A label offset table stores a sequence of label offset entries.
Every label offset entry holds the label name and the offset to its values in the label index section.
They are used to track label index sections. They are read into memory when an index file is loaded.
```
┌─────────────────────┬──────────────────────┐
│ len <4b> │ #entries <4b> │
├─────────────────────┴──────────────────────┤
│ ┌────────────────────────────────────────┐ │
│ │ n = #strs <uvarint> │ │
│ │ n = 1 <1b> │ │
│ ├──────────────────────┬─────────────────┤ │
│ │ len(str_1) <uvarint> │ str_1 <bytes> │ │
│ │ len(name) <uvarint> │ name <bytes> │ │
│ ├──────────────────────┴─────────────────┤ │
│ │ ... │ │
│ │ offset <uvarint64> │ │
│ └────────────────────────────────────────┘ │
│ . . . │
├────────────────────────────────────────────┤
│ CRC32 <4b> │
└────────────────────────────────────────────┘
```
### Postings Offset Table
A postings offset table stores a sequence of postings offset entries.
Every postings offset entry holds the lable name/value pair and the offset to its series list in the postings section.
They are used to track postings sections. They are read into memory when an index file is loaded.
```
┌─────────────────────┬──────────────────────┐
│ len <4b> │ #entries <4b> │
├─────────────────────┴──────────────────────┤
│ ┌────────────────────────────────────────┐ │
│ │ n = 2 <1b> │ │
│ ├──────────────────────┬─────────────────┤ │
│ │ len(str_n) <uvarint> │ str_n <bytes> │ │
│ │ len(name) <uvarint> │ name <bytes> │ │
│ ├──────────────────────┼─────────────────┤ │
│ │ len(value) <uvarint> │ value <bytes> │ │
│ ├──────────────────────┴─────────────────┤ │
│ │ offset <uvarint64> │ │
│ └────────────────────────────────────────┘ │
@ -216,11 +240,11 @@ If a reference is zero, it indicates the respective section does not exist and e
├─────────────────────────────────────────┤
│ ref(label indices start) <8b> │
├─────────────────────────────────────────┤
│ ref(label indices table) <8b> │
│ ref(label offset table) <8b> │
├─────────────────────────────────────────┤
│ ref(postings start) <8b> │
├─────────────────────────────────────────┤
│ ref(postings table) <8b> │
│ ref(postings offset table) <8b> │
├─────────────────────────────────────────┤
│ CRC32 <4b> │
└─────────────────────────────────────────┘