Changes

The name index contains all element and attribute references to the names of a database, all elements and the fixed-size index ids are stored attributes in the main database table. If a database is updated, new names are automatically added. Furthermore, the index is enriched with It contains some basic statistical information, such as the distinct (categorical) or minimum and maximum values number of its elements and attributes. The maximum number occurrence of categories to store per a name can be changed via [[Options#MAXCATS|MAXCATS]]. The index are discarded after [[#Updates|database updates]].

The name index is e.g. applied to pre-evaluate discard location steps that will never yield results:

The path index (which is also called ''path summary'' or ''data guide'') stores all distinct paths of the documents in the database. It contains similar additional statistical information , such as the number of occurrence of a path, its distinct string values, and the minimum/maximum of numeric values. The maximum number of distinct values to store per name indexcan be changed via {{Option|MAXCATS}}. Since {{Version|8.6}}, the distinct values are also stored for elements and attributes of numeric type. The  Various queries will be evaluated much faster if an up-to-date path index are discarded after is available (as can be observed when opening the [[GUI#UpdatesVisualizations|database updatesInfo View]].):

The path index is applied to rewrite descendant * Descendant steps will be rewritten to multiple child steps. Child steps can be are evaluated faster, as fewer nodes have to be accessedtraversed:

* The paths statistics are e.g. used to pre-evaluate the {{Code|fn:count}} functionwill be pre-evaluated by looking up the number in the index: <pre class="brush:xquery"> count(doc('factbook')//country)</pre> * The distinct values of elements or attributes can be looked up in the index as well:

distinct-values(db: will be rewritten and pre-evaluated by the path index :)count( docopen('factbook')//country religions)

In the GUI, index structures can be managed in the dialog windows for creating new databases or displaying the database properties. On command-line, the commands <code>[[Commands#CREATE INDEX{{Command|CREATE INDEX]]</code> }} and <code>[[Commands#DROP INDEX{{Command|DROP INDEX]]</code> }} are used to create and drop index structures. With <code>[[Commands#INFO INDEX{{Command|INFO INDEX]]</code>}}, you get some insight into the contents of an index structure, and <code>[[Commands#SET{{Command|SET]]</code> }} allows you to change the index defaults for new databases:

With XQuery, index structures can be created and dropped via [[{{Function|Database Module#db:optimize|db:optimize]]}}:

Matching text nodes can be directly requested from the index with the XQuery function [[{{Function|Database Module#db:text|db:text]]}}. The index contents can be accessed via [[{{Function|Index Module#index:texts|index:texts]]text}}.

The <code>[[Options#UPDINDEX{{Option|UPDINDEX]]</code> }} option can be activated to keep this index up-to-date., for example: <pre class="brush:xquery">db:optimize( 'mydb', true(), map { 'updindex':true(), 'textindex': true(), 'textinclude':'id' })</pre>

Text nodes can directly be retrieved from the index via the XQuery function [[{{Function|Database Module#db:text-range|db:text-range]]}}.

Attribute nodes can directly be retrieved from the index with the XQuery functions [[{{Function|Database Module#db:attribute|db:attribute]] }} and [[{{Function|Database Module#db:attribute-range|db:attribute-range]]}}. The index contents can be accessed with [[{{Function|Index Module#index:attributes|index:attributes]]}}.

The [[Options#UPDINDEX{{Option|UPDINDEX]] }} option can be activated to keep this index up-to-date.

Attributes with tokens can be directly retrieved from the index with the XQuery function [[{{Function|Database Module#db:token|db:token]]}}. The index contents can be accessed with [[{{Function|Index Module#index:tokens|index:tokens]]}}.

The index provides support for the following full-text features (the values can be changed in the GUI or via the <code>[[Commands#SET{{Command|SET]]</code> }} command):

* '''Stemming''': tokens are stemmed before being indexed (see <code>[[Options#STEMMINGoption: {{Option|STEMMING]]</code>}})* '''Case Sensitive''': tokens are indexed in case-sensitive mode (see <code>[[Options#CASESENSoption: {{Option|CASESENS]]</code>}})* '''Diacritics''': diacritics are indexed as well (see <code>[[Options#DIACRITICSoption: {{Option|DIACRITICS]]</code>}})* '''Stopword List''': a stop word list can be defined to reduce the number of indexed tokens (see <code>[[Options#STOPWORDSoption: {{Option|STOPWORDS]]</code>}})* '''Language''': see [[Full-Text#Languages|Languages]] for more details (see <code>[[Options#LANGUAGEoption: {{Option|LANGUAGE]]</code>}})

Text nodes can be directly requested from the index via the XQuery function [[{{Function|Full-Text Module#ft:search|ft:search]]}}. The index contents can be accessed with [[{{Function|Full-Text Module#ft:tokens|ft:tokens]]}}.

{{Mark|Updated with Version 8.4:}} {{Code|TOKENINCLUDE}} option added Value indexing can be restricted to specific elements and attributes. The nodes to be indexed can be restricted via the <code>[[Options#TEXTINCLUDE{{Option|TEXTINCLUDE]]</code>}}, <code>[[Options#ATTRINCLUDE{{Option|ATTRINCLUDE]]</code>}}, <code>[[Options#TOKENINCLUDE{{Option|TOKENINCLUDE]]</code> }} and <code>[[Options#FTINCLUDE{{Option|FTINCLUDE]]</code> }} options. The options take a list of name patterns, which are separated by commas. The following name patterns are supported:

The options can either be specified via the <code>[[Commands#SET{{Command|SET]]</code> }} command or via XQuery. With the following operations, an attribute index is created for all {{Code|id}} and {{Code|name}} attributes:

With <code>[[Commands#CREATE INDEX{{Command|CREATE INDEX]]</code> }} and [[{{Function|Database Module#db:optimize|db:optimize]]}}, new selective indexing options will ba applied to an existing database. ==Enforce Rewritings== In various cases, existing index structures will not be utilized by the query optimizer. This is usually the case if the name of the database is not a static string (e.g., because it is bound to a variable or passed on as argument of a function call). Furthermore, several candidates for index rewritings may exist, and the query optimizer may decide for a rewriting that turns out to be suboptimal. With {{Version|9.0}}, the {{Option|ENFORCEINDEX}} option was introduced, which allows you to enforce certain index rewritings. While the option can be globally enabled, it is usually better to supply it as [[XQuery Extensions#Pragmas|Pragma]]. Two examples: * In the query below, 10 databases will be addressed. If it is known in advance that these databases contain an up-to-date text index, the index rewriting can be enforced as follows: <pre class="brush:xquery">(# db:enforceindex #) { for $n in 1 to 10 let $db := 'persons' || $n return db:open($db)//person[name/text() = 'John']}</pre> * The following query contains two predicates that may both be rewritten for index access. If the automatically chosen rewriting is known not to be optimal, another index rewriting can enforced by surrounding the specific expression with the pragma: <pre class="brush:xquery">db:open('factbook')//country [(# db:enforceindex #) { @population > '10000000' and @population < '10999999' }] [religions/text() = 'Protestant']</pre> Please note that: * The option should only be enabled if the addressed databases exist, have all required index structures and are up-to-date (otherwise, you will be given an error message).* The enforcement of index rewritings gives you no guarantee that an index will be used. There are many expressions that cannot be rewritten for index access.* If you have more than one enforce pragma in a single path expression, only the first will be considered. =Custom Index Structures= With XQuery, it is comparatively easy to create your own, custom index structures. The following query demonstrate how you can create a {{Code|factbook-index}} database, which contains all texts of the original database in lower case: <pre class="brush:xquery">let $db := 'factbook' let $index := <index>{ for $nodes in db:open($db)//text() group by $text := lower-case($nodes) return <text string='{ $text }'>{ for $node in $nodes return <id>{ db:node-id($node ) }</id> }</text>}</index> return db:create($db || '-index', $index, $db || '-index.xml')</pre> In the following query, a text string is searched, and the text nodes of the original database are retrieved: <pre class="brush:xquery">let $db := 'factbook'let $text := 'italian'for $id in db:open($db || '-index')//*[@string = $text]/idreturn db:open-id($db, $id)/..</pre> With some extra effort, and if {{Option|UPDINDEX}} is enabled for both your original and your index database (see below), your index database will support updates as well (try it, it’s fun!).

Updates in BaseX Generally, update operations are generally very fastin BaseX. By default, because the index structures will be invalidated by updates. As ; as a result, subsequent queries that benefit from index structures may be executed more slowly than before the updateslow down after updates. There are different alternatives to cope with this:

* After the execution of one or more update operations, the <code>[[Commands#OPTIMIZE{{Command|OPTIMIZE]]</code> }} command or the [[{{Function|Database Module#db:optimize|db:optimize]] }} function can be called to rebuild the index structures.* The <code>[[Options#UPDINDEX{{Option|UPDINDEX]]</code> }} option can be activated before creating or optimizing the database. As a result, the text, attribute and token indexes will be incrementally updated after each database update. Please note that incremental updates are not available for the full-text index and database statistics. This is also explains why the up-to-date UPTODATE flag, which is e.g. displayed via <code>[[Commands#INFO DB{{Command|INFO DB]]</code> }} or [[Database_Module#db:info{{Function|Database|db:info]]}}, will be set to {{Code|false}} until the database will be optimized again(various optimizations won’t be triggered. For example, count(//item) can be extremely fast if all meta data is up-to-date.* The <code>[[Options#AUTOOPTIMIZE{{Option|AUTOOPTIMIZE]]</code> }} option can be enabled before creating or optimizing the database. All outdated index structures and statistics will then be recreated after each database update. This option should only be used done for small and medium-sized databases.* Both options can be used side by side: {{Option|UPDINDEX}} will take care that the value index structures will be updated as part of the actual update operation. {{Option|AUTOOPTIMIZE}} will update the remaining data structures (full-text index, database statistics).