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431
Docs/manual.texi
431
Docs/manual.texi
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@ -120,6 +120,7 @@ version see the relevant distribution.
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* Tutorial:: @strong{MySQL} Tutorial
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* Server:: @strong{MySQL} Server
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* Replication:: Replication
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* Fulltext Search:: Fulltext Search
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* Performance:: Getting maximum performance from @strong{MySQL}
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* MySQL Benchmarks:: The @strong{MySQL} benchmark suite
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* Tools:: @strong{MySQL} Utilities
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@ -600,6 +601,13 @@ Replication in MySQL
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* Replication FAQ:: Frequently Asked Questions about replication
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* Replication Problems:: Troubleshooting Replication.
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MySQL Full-text Search
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* Fulltext Search::
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* Fulltext Fine-tuning::
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* Fulltext Features to Appear in MySQL 4.0::
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* Fulltext TODO::
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Getting Maximum Performance from MySQL
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* Optimize Basics:: Optimization overview
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@ -868,15 +876,8 @@ How MySQL Compares to @code{mSQL}
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MySQL Internals
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* MySQL threads:: MySQL threads
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* MySQL full-text search:: MySQL full-text search
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* MySQL test suite:: MySQL test suite
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MySQL Full-text Search
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* Fulltext Fine-tuning::
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* Fulltext features to appear in MySQL 4.0::
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* Fulltext TODO::
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Credits
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* Developers::
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@ -15379,7 +15380,7 @@ In @strong{MySQL} Version 3.23.23 or later, you can also create special
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@code{MyISAM} table type supports @code{FULLTEXT} indexes. They can be
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created only from @code{VARCHAR} and @code{TEXT} columns.
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Indexing always happens over the entire column and partial indexing is not
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supported. See @ref{MySQL full-text search} for details.
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supported. See @ref{Fulltext Search} for details.
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@cindex multi-column indexes
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@cindex indexes, multi-column
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@ -16122,7 +16123,7 @@ For @code{MATCH ... AGAINST()} to work, a @strong{FULLTEXT} index
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must be created first. @xref{CREATE TABLE, , @code{CREATE TABLE}}.
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@code{MATCH ... AGAINST()} is available in @strong{MySQL} Version
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3.23.23 or later. For details and usage examples
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@pxref{MySQL full-text search}.
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@pxref{Fulltext Search}.
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@end table
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@findex casts
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@ -18496,7 +18497,7 @@ In @strong{MySQL} Version 3.23.23 or later, you can also create special
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@code{MyISAM} table type supports @code{FULLTEXT} indexes. They can be created
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only from @code{VARCHAR} and @code{TEXT} columns.
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Indexing always happens over the entire column, partial indexing is not
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supported. See @ref{MySQL full-text search} for details of operation.
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supported. See @ref{Fulltext Search} for details of operation.
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@item
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The @code{FOREIGN KEY}, @code{CHECK}, and @code{REFERENCES} clauses don't
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@ -22675,7 +22676,7 @@ For more information about how @strong{MySQL} uses indexes, see
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@code{FULLTEXT} indexes can index only @code{VARCHAR} and
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@code{TEXT} columns, and only in @code{MyISAM} tables. @code{FULLTEXT} indexes
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are available in @strong{MySQL} Version 3.23.23 and later.
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@ref{MySQL full-text search}.
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@ref{Fulltext Search}.
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@findex DROP INDEX
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@node DROP INDEX, Comments, CREATE INDEX, Reference
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@ -26913,7 +26914,7 @@ tables}.
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@cindex increasing, speed
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@cindex speed, increasing
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@cindex databases, replicating
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@node Replication, Performance, Server, Top
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@node Replication, Fulltext Search, Server, Top
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@chapter Replication in MySQL
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@menu
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* Replication Intro:: Introduction
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@ -27871,10 +27872,208 @@ Once you have collected the evidence on the phantom problem, try hard to
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isolate it into a separate test case first. Then report the problem to
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@email{bugs@@lists.mysql.com} with as much info as possible.
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@cindex searching, full-text
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@cindex full-text search
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@cindex FULLTEXT
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@node Fulltext Search, Performance, Replication, Top
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@chapter MySQL Full-text Search
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Since Version 3.23.23, @strong{MySQL} has support for full-text indexing
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and searching. Full-text indexes in @strong{MySQL} are an index of type
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@code{FULLTEXT}. @code{FULLTEXT} indexes can be created from @code{VARCHAR}
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and @code{TEXT} columns at @code{CREATE TABLE} time or added later with
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@code{ALTER TABLE} or @code{CREATE INDEX}. For large datasets, adding
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@code{FULLTEXT} index with @code{ALTER TABLE} (or @code{CREATE INDEX}) would
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be much faster than inserting rows into the empty table with a @code{FULLTEXT}
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index.
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Full-text search is performed with the @code{MATCH} function.
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@example
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mysql> CREATE TABLE t (a VARCHAR(200), b TEXT, FULLTEXT (a,b));
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Query OK, 0 rows affected (0.00 sec)
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mysql> INSERT INTO t VALUES
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-> ('MySQL has now support', 'for full-text search'),
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-> ('Full-text indexes', 'are called collections'),
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-> ('Only MyISAM tables','support collections'),
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-> ('Function MATCH ... AGAINST()','is used to do a search'),
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-> ('Full-text search in MySQL', 'implements vector space model');
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Query OK, 5 rows affected (0.00 sec)
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Records: 5 Duplicates: 0 Warnings: 0
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mysql> SELECT * FROM t WHERE MATCH (a,b) AGAINST ('MySQL');
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+---------------------------+-------------------------------+
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| a | b |
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+---------------------------+-------------------------------+
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| MySQL has now support | for full-text search |
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| Full-text search in MySQL | implements vector-space-model |
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+---------------------------+-------------------------------+
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2 rows in set (0.00 sec)
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mysql> SELECT *,MATCH a,b AGAINST ('collections support') as x FROM t;
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+------------------------------+-------------------------------+--------+
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| a | b | x |
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+------------------------------+-------------------------------+--------+
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| MySQL has now support | for full-text search | 0.3834 |
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| Full-text indexes | are called collections | 0.3834 |
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| Only MyISAM tables | support collections | 0.7668 |
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| Function MATCH ... AGAINST() | is used to do a search | 0 |
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| Full-text search in MySQL | implements vector space model | 0 |
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+------------------------------+-------------------------------+--------+
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5 rows in set (0.00 sec)
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@end example
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The function @code{MATCH} matches a natural language query @code{AGAINST}
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a text collection (which is simply the columns that are covered by a
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@code{FULLTEXT} index). For every row in a table it returns relevance -
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a similarity measure between the text in that row (in the columns that are
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part of the collection) and the query. When it is used in a @code{WHERE}
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clause (see example above) the rows returned are automatically sorted with
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relevance decreasing. Relevance is a non-negative floating-point number.
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Zero relevance means no similarity. Relevance is computed based on the
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number of words in the row, the number of unique words in that row, the
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total number of words in the collection, and the number of documents (rows)
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that contain a particular word.
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MySQL uses a very simple parser to split text into words. A ``word'' is
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any sequence of letters, numbers, @samp{'}, and @samp{_}. Any ``word''
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that is present in the stopword list or just too short (3 characters
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or less) is ignored.
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Every correct word in the collection and in the query is weighted,
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according to its significance in the query or collection. This way, a
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word that is present in many documents will have lower weight (and may
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even have a zero weight), because it has lower semantic value in this
|
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particular collection. Otherwise, if the word is rare, it will receive a
|
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higher weight. The weights of the words are then combined to compute the
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relevance of the row.
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Such a technique works best with large collections (in fact, it was
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carefully tuned this way). For very small tables, word distribution
|
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does not reflect adequately their semantical value, and this model
|
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may sometimes produce bizarre results.
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For example, search for the word "search" will produce no results in the
|
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above example. Word "search" is present in more than half of rows, and
|
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as such, is effectively treated as a stopword (that is, with semantical value
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zero). It is, really, the desired behavior - a natural language query
|
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should not return every other row in 1GB table.
|
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|
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A word that matches half of rows in a table is less likely to locate relevant
|
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documents. In fact, it will most likely find plenty of irrelevant documents.
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We all know this happens far too often when we are trying to find something on
|
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the Internet with a search engine. It is with this reasoning that such rows
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have been assigned a low semantical value in @strong{a particular dataset}.
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@menu
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* Fulltext Fine-tuning::
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* Fulltext Features to Appear in MySQL 4.0::
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* Fulltext TODO::
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@end menu
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@node Fulltext Fine-tuning, Fulltext Features to Appear in MySQL 4.0, , Fulltext Search
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@section Fine-tuning MySQL Full-text Search
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Unfortunately, full-text search has no user-tunable parameters yet,
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although adding some is very high on the TODO. However, if you have a
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@strong{MySQL} source distribution (@xref{Installing source}.), you can
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somewhat alter the full-text search behavior.
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Note that full-text search was carefully tuned for the best searching
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effectiveness. Modifying the default behavior will, in most cases,
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only make the search results worse. Do not alter the @strong{MySQL} sources
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unless you know what you are doing!
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@itemize
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@item
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Minimal length of word to be indexed is defined in
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@code{myisam/ftdefs.h} file by the line
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@example
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#define MIN_WORD_LEN 4
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@end example
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Change it to the value you prefer, recompile @strong{MySQL}, and rebuild
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your @code{FULLTEXT} indexes.
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@item
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The stopword list is defined in @code{myisam/ft_static.c}
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Modify it to your taste, recompile @strong{MySQL} and rebuild
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your @code{FULLTEXT} indexes.
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@item
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The 50% threshold is caused by the particular weighting scheme chosen. To
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disable it, change the following line in @code{myisam/ftdefs.h}:
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@example
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#define GWS_IN_USE GWS_PROB
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@end example
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to
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@example
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#define GWS_IN_USE GWS_FREQ
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@end example
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and recompile @strong{MySQL}.
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There is no need to rebuild the indexes in this case.
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@end itemize
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@node Fulltext Features to Appear in MySQL 4.0, Fulltext TODO, Fulltext Fine-tuning, Fulltext Search
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@section New Features of Full-text Search to Appear in MySQL 4.0
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This section includes a list of the fulltext features that are already
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implemented in the 4.0 tree. It explains
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@strong{More functions for full-text search} entry of @ref{TODO MySQL 4.0}.
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@itemize @bullet
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@item @code{REPAIR TABLE} with @code{FULLTEXT} indexes,
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@code{ALTER TABLE} with @code{FULLTEXT} indexes, and
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@code{OPTIMIZE TABLE} with @code{FULLTEXT} indexes are now
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up to 100 times faster.
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@item @code{MATCH ... AGAINST} now supports the following
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@strong{boolean operators}:
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@itemize @bullet
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@item @code{+}word means the that word @strong{must} be present in every
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row returned.
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@item @code{-}word means the that word @strong{must not} be present in every
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row returned.
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@item @code{<} and @code{>} can be used to decrease and increase word
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weight in the query.
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@item @code{~} can be used to assign a @strong{negative} weight to a noise
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word.
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@item @code{*} is a truncation operator.
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@end itemize
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Boolean search utilizes a more simplistic way of calculating the relevance,
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that does not have a 50% threshold.
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@item Searches are now up to 2 times faster due to optimized search algorithm.
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@item Utility program @code{ft_dump} added for low-level @code{FULLTEXT}
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index operations (querying/dumping/statistics).
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@end itemize
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@node Fulltext TODO, , Fulltext Features to Appear in MySQL 4.0, Fulltext Search
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@section Full-text Search TODO
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@itemize @bullet
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@item Make all operations with @code{FULLTEXT} index @strong{faster}.
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@item Support for braces @code{()} in boolean full-text search.
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@item Support for "always-index words". They could be any strings
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the user wants to treat as words, examples are "C++", "AS/400", "TCP/IP", etc.
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@item Support for full-text search in @code{MERGE} tables.
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@item Support for multi-byte charsets.
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@item Make stopword list to depend of the language of the data.
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@item Stemming (dependent of the language of the data, of course).
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@item Generic user-supplyable UDF (?) preparser.
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@item Make the model more flexible (by adding some adjustable
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parameters to @code{FULLTEXT} in @code{CREATE/ALTER TABLE}).
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@end itemize
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@cindex performance, maximizing
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@cindex optimization
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@node Performance, MySQL Benchmarks, Replication, Top
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@node Performance, MySQL Benchmarks, Fulltext Search, Top
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@chapter Getting Maximum Performance from MySQL
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Optimization is a complicated task because it ultimately requires
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|
|
@ -40160,11 +40359,10 @@ This is a relatively low traffic list, in comparison with
|
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@menu
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* MySQL threads:: MySQL threads
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* MySQL full-text search:: MySQL full-text search
|
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* MySQL test suite:: MySQL test suite
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@end menu
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@node MySQL threads, MySQL full-text search, MySQL internals, MySQL internals
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@node MySQL threads, MySQL test suite, , MySQL internals
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@section MySQL Threads
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The @strong{MySQL} server creates the following threads:
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|
|
@ -40211,208 +40409,9 @@ started to read and apply updates from the master.
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@code{mysqladmin processlist} only shows the connection, @code{INSERT DELAYED},
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and replication threads.
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|
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@cindex searching, full-text
|
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@cindex full-text search
|
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@cindex FULLTEXT
|
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@node MySQL full-text search, MySQL test suite, MySQL threads, MySQL internals
|
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@section MySQL Full-text Search
|
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|
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Since Version 3.23.23, @strong{MySQL} has support for full-text indexing
|
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and searching. Full-text indexes in @strong{MySQL} are an index of type
|
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@code{FULLTEXT}. @code{FULLTEXT} indexes can be created from @code{VARCHAR}
|
||||
and @code{TEXT} columns at @code{CREATE TABLE} time or added later with
|
||||
@code{ALTER TABLE} or @code{CREATE INDEX}. For large datasets, adding
|
||||
@code{FULLTEXT} index with @code{ALTER TABLE} (or @code{CREATE INDEX}) would
|
||||
be much faster than inserting rows into the empty table with a @code{FULLTEXT}
|
||||
index.
|
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|
||||
Full-text search is performed with the @code{MATCH} function.
|
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|
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@example
|
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mysql> CREATE TABLE t (a VARCHAR(200), b TEXT, FULLTEXT (a,b));
|
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Query OK, 0 rows affected (0.00 sec)
|
||||
|
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mysql> INSERT INTO t VALUES
|
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-> ('MySQL has now support', 'for full-text search'),
|
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-> ('Full-text indexes', 'are called collections'),
|
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-> ('Only MyISAM tables','support collections'),
|
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-> ('Function MATCH ... AGAINST()','is used to do a search'),
|
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-> ('Full-text search in MySQL', 'implements vector space model');
|
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Query OK, 5 rows affected (0.00 sec)
|
||||
Records: 5 Duplicates: 0 Warnings: 0
|
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|
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mysql> SELECT * FROM t WHERE MATCH (a,b) AGAINST ('MySQL');
|
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+---------------------------+-------------------------------+
|
||||
| a | b |
|
||||
+---------------------------+-------------------------------+
|
||||
| MySQL has now support | for full-text search |
|
||||
| Full-text search in MySQL | implements vector-space-model |
|
||||
+---------------------------+-------------------------------+
|
||||
2 rows in set (0.00 sec)
|
||||
|
||||
mysql> SELECT *,MATCH a,b AGAINST ('collections support') as x FROM t;
|
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+------------------------------+-------------------------------+--------+
|
||||
| a | b | x |
|
||||
+------------------------------+-------------------------------+--------+
|
||||
| MySQL has now support | for full-text search | 0.3834 |
|
||||
| Full-text indexes | are called collections | 0.3834 |
|
||||
| Only MyISAM tables | support collections | 0.7668 |
|
||||
| Function MATCH ... AGAINST() | is used to do a search | 0 |
|
||||
| Full-text search in MySQL | implements vector space model | 0 |
|
||||
+------------------------------+-------------------------------+--------+
|
||||
5 rows in set (0.00 sec)
|
||||
@end example
|
||||
|
||||
The function @code{MATCH} matches a natural language query @code{AGAINST}
|
||||
a text collection (which is simply the columns that are covered by a
|
||||
@strong{FULLTEXT} index). For every row in a table it returns relevance -
|
||||
a similarity measure between the text in that row (in the columns that are
|
||||
part of the collection) and the query. When it is used in a @code{WHERE}
|
||||
clause (see example above) the rows returned are automatically sorted with
|
||||
relevance decreasing. Relevance is a non-negative floating-point number.
|
||||
Zero relevance means no similarity. Relevance is computed based on the
|
||||
number of words in the row, the number of unique words in that row, the
|
||||
total number of words in the collection, and the number of documents (rows)
|
||||
that contain a particular word.
|
||||
|
||||
MySQL uses a very simple parser to split text into words. A ``word'' is
|
||||
any sequence of letters, numbers, @samp{'}, and @samp{_}. Any ``word''
|
||||
that is present in the stopword list or just too short (3 characters
|
||||
or less) is ignored.
|
||||
|
||||
Every correct word in the collection and in the query is weighted,
|
||||
according to its significance in the query or collection. This way, a
|
||||
word that is present in many documents will have lower weight (and may
|
||||
even have a zero weight), because it has lower semantic value in this
|
||||
particular collection. Otherwise, if the word is rare, it will receive a
|
||||
higher weight. The weights of the words are then combined to compute the
|
||||
relevance of the row.
|
||||
|
||||
Such a technique works best with large collections (in fact, it was
|
||||
carefully tuned this way). For very small tables, word distribution
|
||||
does not reflect adequately their semantical value, and this model
|
||||
may sometimes produce bizarre results.
|
||||
|
||||
For example, search for the word "search" will produce no results in the
|
||||
above example. Word "search" is present in more than half of rows, and
|
||||
as such, is effectively treated as a stopword (that is, with semantical value
|
||||
zero). It is, really, the desired behavior - a natural language query
|
||||
should not return every other row in 1GB table.
|
||||
|
||||
A word that matches half of rows in a table is less likely to locate relevant
|
||||
documents. In fact, it will most likely find plenty of irrelevant documents.
|
||||
We all know this happens far too often when we are trying to find something on
|
||||
the Internet with a search engine. It is with this reasoning that such rows
|
||||
have been assigned a low semantical value in @strong{a particular dataset}.
|
||||
|
||||
@menu
|
||||
* Fulltext Fine-tuning::
|
||||
* Fulltext features to appear in MySQL 4.0::
|
||||
* Fulltext TODO::
|
||||
@end menu
|
||||
|
||||
@node Fulltext Fine-tuning, Fulltext features to appear in MySQL 4.0, MySQL full-text search, MySQL full-text search
|
||||
@subsection Fine-tuning MySQL Full-text Search
|
||||
|
||||
Unfortunately, full-text search has no user-tunable parameters yet,
|
||||
although adding some is very high on the TODO. However, if you have a
|
||||
@strong{MySQL} source distribution (@xref{Installing source}.), you can
|
||||
somewhat alter the full-text search behavior.
|
||||
|
||||
Note that full-text search was carefully tuned for the best searching
|
||||
effectiveness. Modifying the default behavior will, in most cases,
|
||||
only make the search results worse. Do not alter the @strong{MySQL} sources
|
||||
unless you know what you are doing!
|
||||
|
||||
@itemize
|
||||
|
||||
@item
|
||||
Minimal length of word to be indexed is defined in
|
||||
@code{myisam/ftdefs.h} file by the line
|
||||
@example
|
||||
#define MIN_WORD_LEN 4
|
||||
@end example
|
||||
Change it to the value you prefer, recompile @strong{MySQL}, and rebuild
|
||||
your @code{FULLTEXT} indexes.
|
||||
|
||||
@item
|
||||
The stopword list is defined in @code{myisam/ft_static.c}
|
||||
Modify it to your taste, recompile @strong{MySQL} and rebuild
|
||||
your @code{FULLTEXT} indexes.
|
||||
|
||||
@item
|
||||
The 50% threshold is caused by the particular weighting scheme chosen. To
|
||||
disable it, change the following line in @code{myisam/ftdefs.h}:
|
||||
@example
|
||||
#define GWS_IN_USE GWS_PROB
|
||||
@end example
|
||||
to
|
||||
@example
|
||||
#define GWS_IN_USE GWS_FREQ
|
||||
@end example
|
||||
and recompile @strong{MySQL}.
|
||||
There is no need to rebuild the indexes in this case.
|
||||
|
||||
@end itemize
|
||||
|
||||
@node Fulltext features to appear in MySQL 4.0, Fulltext TODO, Fulltext Fine-tuning, MySQL full-text search
|
||||
@subsection New Features of Full-text Search to Appear in MySQL 4.0
|
||||
|
||||
This section includes a list of the fulltext features that are already
|
||||
implemented in the 4.0 tree. It explains
|
||||
@strong{More functions for full-text search} entry of @ref{TODO MySQL 4.0}.
|
||||
|
||||
@itemize @bullet
|
||||
@item @code{REPAIR TABLE} with @code{FULLTEXT} indexes,
|
||||
@code{ALTER TABLE} with @code{FULLTEXT} indexes, and
|
||||
@code{OPTIMIZE TABLE} with @code{FULLTEXT} indexes are now
|
||||
up to 100 times faster.
|
||||
|
||||
@item @code{MATCH ... AGAINST} now supports the following
|
||||
@strong{boolean operators}:
|
||||
|
||||
@itemize @bullet
|
||||
@item @code{+}word means the that word @strong{must} be present in every
|
||||
row returned.
|
||||
@item @code{-}word means the that word @strong{must not} be present in every
|
||||
row returned.
|
||||
@item @code{<} and @code{>} can be used to decrease and increase word
|
||||
weight in the query.
|
||||
@item @code{~} can be used to assign a @strong{negative} weight to a noise
|
||||
word.
|
||||
@item @code{*} is a truncation operator.
|
||||
@end itemize
|
||||
|
||||
Boolean search utilizes a more simplistic way of calculating the relevance,
|
||||
that does not have a 50% threshold.
|
||||
|
||||
@item Searches are now up to 2 times faster due to optimized search algorithm.
|
||||
|
||||
@item Utility program @code{ft_dump} added for low-level @code{FULLTEXT}
|
||||
index operations (querying/dumping/statistics).
|
||||
|
||||
@end itemize
|
||||
|
||||
@node Fulltext TODO, , Fulltext features to appear in MySQL 4.0, MySQL full-text search
|
||||
@subsection Full-text Search TODO
|
||||
|
||||
@itemize @bullet
|
||||
@item Make all operations with @code{FULLTEXT} index @strong{faster}.
|
||||
@item Support for braces @code{()} in boolean fulltext search.
|
||||
@item Support for "always-index words". They could be any strings
|
||||
the user wants to treat as words, examples are "C++", "AS/400", "TCP/IP", etc.
|
||||
@item Support for fulltext search in @code{MERGE} tables.
|
||||
@item Support for multi-byte charsets.
|
||||
@item Make stopword list to depend of the language of the data.
|
||||
@item Stemming (dependent of the language of the data, of course).
|
||||
@item Generic user-supplyable UDF (?) preparser.
|
||||
@item Make the model more flexible (by adding some adjustable
|
||||
parameters to @code{FULLTEXT} in @code{CREATE/ALTER TABLE}).
|
||||
@end itemize
|
||||
|
||||
@cindex mysqltest, MySQL Test Suite
|
||||
@cindex testing mysqld, mysqltest
|
||||
@node MySQL test suite, , MySQL full-text search, MySQL internals
|
||||
@node MySQL test suite, , MySQL threads, MySQL internals
|
||||
@section MySQL Test Suite
|
||||
|
||||
Until recently, our main full-coverage test suite was based on proprietary
|
||||
|
|
@ -47563,7 +47562,7 @@ the @code{.MYD} file.
|
|||
Better replication.
|
||||
@item
|
||||
More functions for full-text search.
|
||||
@xref{Fulltext features to appear in MySQL 4.0}.
|
||||
@xref{Fulltext Features to Appear in MySQL 4.0}.
|
||||
@item
|
||||
Character set casts and syntax for handling multiple character sets.
|
||||
@item
|
||||
|
|
|
|||
Loading…
Add table
Reference in a new issue