Escaping characters in query string

As some characters are used as operators in the query string, they should be escaped to avoid query errors or unwanted matching conditions.

The following characters should be escaped using backslash (\):

!    "    $    '    (    )    -    /    <    @    \    ^    |    ~
SELECT * FROM your_index WHERE MATCH('l\'italiano');

Use double backslash to escape all other characters.

SELECT * FROM your_index WHERE MATCH('r\\&b | \\(official video\\)');

Pay attention that in order to escape backslash character you should use "\\\\" syntax.

SELECT * FROM your_index WHERE MATCH('\\\\ABC');

Also, if you run your queries using some programming language don't forget about a mysql escaping function (e.g., mysqli_real_escape_string in PHP or conn.escape_string in Python) to escape these characters the same way as described above.

Search profiling

How a query is interpreted

Example of a complex query:

"hello world" @title "example program"~5 @body python -(php|perl) @* code

The full meaning of this search is:

  • Find the words 'hello' and 'world' adjacently in any field in a document;
  • Additionally, the same document must also contain the words 'example' and 'program' in the title field, with up to, but not including, 5 words between the words in question; (E.g. "example PHP program" would be matched however "example script to introduce outside data into the correct context for your program" would not because two terms have 5 or more words between them)
  • Additionally, the same document must contain the word 'python' in the body field, but not contain either 'php' or 'perl';
  • Additionally, the same document must contain the word 'code' in any field.

OR operator precedence is higher than AND, so "looking for cat | dog | mouse" means "looking for ( cat | dog | mouse )" and not "(looking for cat) | dog | mouse".

To understand how a query will be executed, Manticore Search offer query profile tooling for viewing the query tree created by a query expression.

Profiling the query tree in SQL

When using SQL statement the full-text query profiling needs to be enabled before running the desired query:

SET profiling =1;
SELECT * FROM test WHERE MATCH('@title abc* @body hey');

To view the query tree, we must run SHOW PLAN right after the execution of the query:

SHOW PLAN;

The command will return the structure of the executed query. Please note that the 3 statements - SET profiling, the query and SHOW - must run on the same session.

Profiling the query in HTTP

In HTTP, we can just enable "profile":true to get in response the full-text query tree structure.

{
  "index":"test",
  "profile":true,
  "query":
  {
    "match_phrase": { "_all" : "had grown quite" }
  }
}

The response will contain a profile object in which we can find a member query.

query property contains the transformed full-text query tree. Each node contains:

  • type: node type. Can be AND, OR, PHRASE, KEYWORD etc.
  • description: query subtree for this node shown as a string (in SHOW PLAN format)
  • children: child nodes, if any
  • max_field_pos: maximum position within a field

A keyword node will also provide:

  • word: transformed keyword.
  • querypos: position of this keyword in a query.
  • excluded: keyword excluded from query.
  • expanded: keyword added by prefix expansion.
  • field_start: keyword must occur at the very start of the field.
  • field_end: keyword must occur at the very end of the field.
  • boost: keyword IDF will be multiplied by this.
📋
SET profiling=1;
SELECT * FROM test WHERE MATCH('@title abc* @body hey');
SHOW PLAN \G
Response
*************************** 1\. row ***************************
Variable: transformed_tree
   Value: AND(
  OR(fields=(title), KEYWORD(abcx, querypos=1, expanded), KEYWORD(abcm, querypos=1, expanded)),
  AND(fields=(body), KEYWORD(hey, querypos=2)))
1 row in set (0.00 sec)

In some cases the evaluated query tree can be rather different from the original one because of expansions and other transformations.

📋
SET profiling=1;

SELECT id FROM forum WHERE MATCH('@title way* @content hey') LIMIT 1;

SHOW PLAN;
Response
Query OK, 0 rows affected (0.00 sec)

+--------+
| id     |
+--------+
| 711651 |
+--------+
1 row in set (0.04 sec)

+------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Variable         | Value                                                                                                                                                                                                                                                                                                                                                                                                                   |
+------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| transformed_tree | AND(
  OR(
    OR(
      AND(fields=(title), KEYWORD(wayne, querypos=1, expanded)),
      OR(
        AND(fields=(title), KEYWORD(ways, querypos=1, expanded)),
        AND(fields=(title), KEYWORD(wayyy, querypos=1, expanded)))),
    AND(fields=(title), KEYWORD(way, querypos=1, expanded)),
    OR(fields=(title), KEYWORD(way*, querypos=1, expanded))),
  AND(fields=(content), KEYWORD(hey, querypos=2))) |
+------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Profiling without running a query

The SQL statement EXPLAIN QUERY allows displaying the execution tree of a provided full-text query without running an actual search query on the index.

SQL
📋
EXPLAIN QUERY index_base '@title running @body dog'\G
Response
 EXPLAIN QUERY index_base '@title running @body dog'\G
*************************** 1\. row ***************************
Variable: transformed_tree
   Value: AND(
      OR(
            AND(fields=(title), KEYWORD(run, querypos=1, morphed)),
            AND(fields=(title), KEYWORD(running, querypos=1, morphed))))
  AND(fields=(body), KEYWORD(dog, querypos=2, morphed)))

Viewing the match factors values

When expression ranker is used, it is possible to expose the values of the calculated factors using PACKEDFACTORS().

The function returns:

  • the values of document level factors (like bm25, field_mask, doc_word_count)
  • list with each field that returned a hit (like lcs, hit_count, word_count sum_idf, min_hit_pos etc.)
  • list with each keyword from the query and their tf and idf values

The values can be used to understand why certain documents get scored lower or higher in a search or to improve the existing ranking expression.

SQL
📋
SELECT id, PACKEDFACTORS() FROM test1 WHERE MATCH('test one') OPTION ranker=expr('1')\G
Response
             id: 1
packedfactors(): bm25=569, bm25a=0.617197, field_mask=2, doc_word_count=2,
    field1=(lcs=1, hit_count=2, word_count=2, tf_idf=0.152356,
        min_idf=-0.062982, max_idf=0.215338, sum_idf=0.152356, min_hit_pos=4,
        min_best_span_pos=4, exact_hit=0, max_window_hits=1, min_gaps=2,
        exact_order=1, lccs=1, wlccs=0.215338, atc=-0.003974),
    word0=(tf=1, idf=-0.062982),
    word1=(tf=1, idf=0.215338)
1 row in set (0.00 sec)

Boolean optimization

Queries may be automatically optimized if OPTION boolean_simplify=1 is specified. Some transformations performed by this optimization include:

  • Excess brackets: ((A | B) | C) becomes ( A | B | C ); ((A B) C) becomes ( A B C )
  • Excess AND NOT: ((A !N1) !N2) becomes (A !(N1 | N2))
  • Common NOT: ((A !N) | (B !N)) becomes ((A|B) !N)
  • Common Compound NOT: ((A !(N AA)) | (B !(N BB))) becomes (((A|B) !N) | (A !AA) | (B !BB)) if the cost of evaluating N is greater than the added together costs of evaluating A and B
  • Common subterm: ((A (N | AA)) | (B (N | BB))) becomes (((A|B) N) | (A AA) | (B BB)) if the cost of evaluating N is greater than the added together costs of evaluating A and B
  • Common keywords: (A | "A B"~N) becomes A; ("A B" | "A B C") becomes "A B"; ("A B"~N | "A B C"~N) becomes ("A B"~N)
  • Common phrase: ("X A B" | "Y A B") becomes ("("X"|"Y") A B")
  • Common AND NOT: ((A !X) | (A !Y) | (A !Z)) becomes (A !(X Y Z))
  • Common OR NOT: ((A !(N | N1)) | (B !(N | N2))) becomes (( (A !N1) | (B !N2) ) !N) Note that optimizing the queries consumes CPU time, so for simple queries -or for hand-optimized queries- you'll do better with the default boolean_simplify=0 value. Simplifications are often better for complex queries, or algorithmically generated queries.

Queries like "-dog", which implicitly include all documents from the collection, can not be evaluated. This is both for technical and performance reasons. Technically, Manticore does not always keep a list of all IDs. Performance-wise, when the collection is huge (ie. 10-100M documents), evaluating such queries could take very long.