Difference between revisions of "Storage Layout"
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| '''1. Metadata''' | | '''1. Metadata''' | ||
− | | 1. Key/value pairs, in no particular order ({{Type|Token}}/{{Type|Token}}):<br/> • Examples: {{Code|FNAME}}, {{Code|TIME}}, {{Code|SIZE}}, ...<br /> • {{Code|PERM}} → Number of users ({{Type|Num}}), and name/password/permission values for each user ({{Type|Token}}/{{Type|Token}}/{{Type|Num}})<br/>2. Empty key as finalizer | + | | 1. Key/value pairs, in no particular order ({{Type|Token}}/{{Type|Token}}):<br/> • Examples: {{Code|FNAME}}, {{Code|TIME}}, {{Code|SIZE}}, ...<br/> • {{Code|PERM}} → Number of users ({{Type|Num}}), and name/password/permission values for each user ({{Type|Token}}/{{Type|Token}}/{{Type|Num}})<br/>2. Empty key as finalizer |
|- valign="top" | |- valign="top" | ||
| '''2. Main memory indexes''' | | '''2. Main memory indexes''' | ||
− | | 1. Key/value pairs, in no particular order ({{Type|Token}}/{{Type|Token}}):<br /> • {{Code|TAGS}} → Element Name Index<br /> • {{Code|ATTS}} → Attribute Name Index<br /> • {{Code|PATH}} → Path Index<br /> • {{Code|NS}} → Namespaces<br /> • {{Code|DOCS}} → Document Index<br/>2. Empty key as finalizer | + | | 1. Key/value pairs, in no particular order ({{Type|Token}}/{{Type|Token}}):<br/> • {{Code|TAGS}} → Element Name Index<br/> • {{Code|ATTS}} → Attribute Name Index<br/> • {{Code|PATH}} → Path Index<br/> • {{Code|NS}} → Namespaces<br/> • {{Code|DOCS}} → Document Index<br/>2. Empty key as finalizer |
|- valign="top" | |- valign="top" | ||
| '''2 a) Name Index'''<br/>Element/attribute names | | '''2 a) Name Index'''<br/>Element/attribute names | ||
− | | 1. Token set, storing all names ({{Type|TokenSet}})<br />2. One StatsKey instance per entry:<br/>2.1. Content kind ({{Type|Num}}):<br />2.1.1. Number: min/max ({{Type|Doubles}})<br />2.1.2. Category: number of entries ({{Type|Num}}), entries ({{Type|Tokens}})<br />2.2. Number of entries ({{Type|Num}})<br />2.3. Leaf flag ({{Type|Boolean}})<br />2.4. Maximum text length ({{Type|Double}}; legacy, could be {{Type|Num}}) | + | | 1. Token set, storing all names ({{Type|TokenSet}})<br/>2. One StatsKey instance per entry:<br/>2.1. Content kind ({{Type|Num}}):<br/>2.1.1. Number: min/max ({{Type|Doubles}})<br/>2.1.2. Category: number of entries ({{Type|Num}}), entries ({{Type|Tokens}})<br/>2.2. Number of entries ({{Type|Num}})<br/>2.3. Leaf flag ({{Type|Boolean}})<br/>2.4. Maximum text length ({{Type|Double}}; legacy, could be {{Type|Num}}) |
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| '''2 b) Path Index''' | | '''2 b) Path Index''' |
Latest revision as of 10:17, 9 March 2023
This article is part of the Advanced User's Guide. It presents some low-level details on how data is stored in the database files.
Contents
Data Types[edit]
The following data types are used for specifying the storage layout:
Type | Description | Example (native → hex integers) |
---|---|---|
Num
|
Compressed integer (1-5 bytes), specified in Num.java | 15 → 0F ; 511 → 41 FF |
Token
|
Length (Num ) and bytes of UTF8 byte representation
|
Hello → 05 48 65 6c 6c 6f
|
Double
|
Number, stored as token | 123 → 03 31 32 33
|
Boolean
|
Boolean (1 byte, 00 or 01 )
|
true → 01
|
Nums , Tokens , Doubles
|
Arrays of values, introduced with the number of entries | 1,2 → 02 01 31 01 32
|
TokenSet
|
Key array (Tokens ), next/bucket/size arrays (3x Nums )
|
Database Files[edit]
The following tables illustrate the layout of the BaseX database files. All files are suffixed with .basex
.
Metadata, Name/Path/Doc Indexes: inf
[edit]
Description | Format |
---|---|
1. Metadata | 1. Key/value pairs, in no particular order (Token /Token ):• Examples: FNAME , TIME , SIZE , ...• PERM → Number of users (Num ), and name/password/permission values for each user (Token /Token /Num )2. Empty key as finalizer |
2. Main memory indexes | 1. Key/value pairs, in no particular order (Token /Token ):• TAGS → Element Name Index• ATTS → Attribute Name Index• PATH → Path Index• NS → Namespaces• DOCS → Document Index2. Empty key as finalizer |
2 a) Name Index Element/attribute names |
1. Token set, storing all names (TokenSet )2. One StatsKey instance per entry: 2.1. Content kind ( Num ):2.1.1. Number: min/max ( Doubles )2.1.2. Category: number of entries ( Num ), entries (Tokens )2.2. Number of entries ( Num )2.3. Leaf flag ( Boolean )2.4. Maximum text length ( Double ; legacy, could be Num )
|
2 b) Path Index | 1. Flag for path definition (Boolean , always true ; legacy)2. PathNode: 2.1. Name reference ( Num )2.2. Node kind ( Num )2.3. Number of occurrences ( Num )2.4. Number of children ( Num )2.5. Double ; legacy, can be reused or discarded2.6. Recursive generation of child nodes (→ 2) |
2 c) Namespaces | 1. Token set, storing prefixes (TokenSet )2. Token set, storing URIs ( TokenSet )3. NSNode: 3.1. pre value ( Num )3.2. References to prefix/URI pairs ( Nums )3.3. Number of children ( Num )3.4. Recursive generation of child nodes (→ 3) |
2 d) Document Index | Array of integers, representing the distances between all document pre values (Nums )
|
Node Table: tbl
, tbli
[edit]
tbl
: Main database table, stored in blocks.tbli
: Database directory, organizing the database blocks.
Some more information on the node storage is available.
Texts: txt
, atv
[edit]
txt
: Heap file for text values (document names, string values of texts, comments and processing instructions)atv
: Heap file for attribute values.
Value Indexes: txtl
, txtr
, atvl
, atvr
[edit]
Text Index:
txtl
: Heap file with ID lists.txtr
: Index file with references to ID lists.
The Attribute Index is contained in the files atvl
and atvr
, the Token Index in tokl
and tokr
. All have the same layout.
For a more detailed discussion and examples of these file formats please see Index File Structure.
Document Path Index: pth
[edit]
Provides an index of all the document paths in the database. For databases with a large number of paths this file can be quite large so it is only generated the first time a function requesting a path lookup is run. For databases where path lookups are never used this file will not exist.
Note: On Windows/Mac systems this file is case insensitive (all paths are lower case). On UNIX-like systems this file is case sensitive. The behaviour of path look ups will vary between systems. Copying this file between system types may lead to unexpected behaviour.
ID/Pre Mapping: idp
[edit]
This file is only created if incremental indexing (UPDINDEX) is enabled for a database. It is used to provide a quick look up of the pre value for a database node id.
Full-Text Fuzzy Index: ftxx
, ftxy
, ftxz
[edit]
...may soon be reimplemented.