General query settings

SetSelect

Prototype: function SetSelect ( $clause )

Sets the select clause, listing specific attributes to fetch, and Sorting modes to compute and fetch. Clause syntax mimics SQL.

SetSelect() is very similar to the part of a typical SQL query between SELECT and FROM. It lets you choose what attributes (columns) to fetch, and also what expressions over the columns to compute and fetch. A certain difference from SQL is that expressions must always be aliased to a correct identifier (consisting of letters and digits) using ‘AS’ keyword. SQL also lets you do that but does not require to. Manticore enforces aliases so that the computation results can always be returned under a “normal” name in the result set, used in other clauses, etc.

Everything else is basically identical to SQL. Star (‘*’) is supported. Functions are supported. Arbitrary amount of expressions is supported. Computed expressions can be used for sorting, filtering, and grouping, just as the regular attributes.

When using GROUP BY agregate functions (AVG(), MIN(), MAX(), SUM()) are supported.

Expression sorting (Sorting modes) and geodistance functions (SetGeoAnchor) are now internally implemented using this computed expressions mechanism, using magic names ‘@expr’ and ‘@geodist’ respectively.

Example:

$cl->SetSelect ( "*, @weight+(user_karma+ln(pageviews))*0.1 AS myweight" );
$cl->SetSelect ( "exp_years, salary_gbp*{$gbp_usd_rate} AS salary_usd,
   IF(age>40,1,0) AS over40" );
$cl->SetSelect ( "*, AVG(price) AS avgprice" );

SetLimits

Prototype: function SetLimits ( $offset, $limit, $max_matches=1000, $cutoff=0 )

Sets offset into server-side result set ($offset) and amount of matches to return to client starting from that offset ($limit). Can additionally control maximum server-side result set size for current query ($max_matches) and the threshold amount of matches to stop searching at ($cutoff). All parameters must be non-negative integers.

First two parameters to SetLimits() are identical in behavior to MySQL LIMIT clause. They instruct searchd to return at most $limit matches starting from match number $offset. The default offset and limit settings are 0 and 20, that is, to return first 20 matches.

max_matches setting controls how much matches searchd will keep in RAM while searching. All matching documents will be normally processed, ranked, filtered, and sorted even if max_matches is set to 1. But only best N documents are stored in memory at any given moment for performance and RAM usage reasons, and this setting controls that N. Note that there are two places where max_matches limit is enforced. Per-query limit is controlled by this API call, but there also is per-server limit controlled by max_matches setting in the config file. To prevent RAM usage abuse, server will not allow to set per-query limit higher than the per-server limit.

You can’t retrieve more than max_matches matches to the client application. The default limit is set to 1000. Normally, you must not have to go over this limit. One thousand records is enough to present to the end user. And if you’re thinking about pulling the results to application for further sorting or filtering, that would be much more efficient if performed on Manticore side.

$cutoff setting is intended for advanced performance control. It tells searchd to forcibly stop search query once $cutoff matches had been found and processed.

SetMaxQueryTime

Prototype: function SetMaxQueryTime ( $max_query_time )

Sets maximum search query time, in milliseconds. Parameter must be a non-negative integer. Default value is 0 which means “do not limit”.

Similar to $cutoff setting from SetLimits(), but limits elapsed query time instead of processed matches count. Local search queries will be stopped once that much time has elapsed. Note that if you’re performing a search which queries several local indexes, this limit applies to each index separately.

SetOverride

DEPRECATED

Prototype: function SetOverride ( $attrname, $attrtype, $values )

Sets temporary (per-query) per-document attribute value overrides. Only supports scalar attributes. $values must be a hash that maps document IDs to overridden attribute values.

Override feature lets you “temporary” update attribute values for some documents within a single query, leaving all other queries unaffected. This might be useful for personalized data. For example, assume you’re implementing a personalized search function that wants to boost the posts that the user’s friends recommend. Such data is not just dynamic, but also personal; so you can’t simply put it in the index because you don’t want everyone’s searches affected. Overrides, on the other hand, are local to a single query and invisible to everyone else. So you can, say, setup a “friends_weight” value for every document, defaulting to 0, then temporary override it with 1 for documents 123, 456 and 789 (recommended by exactly the friends of current user), and use that value when ranking.