The Ultimate Guide to High Availability with MariaDB

TEXT

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Syntax

TEXT[(M)] [CHARACTER SET charset_name] [COLLATE collation_name]

Description

A TEXT column with a maximum length of 65,535 (216 - 1) characters. The effective maximum length is less if the value contains multi-byte characters. Each TEXT value is stored using a two-byte length prefix that indicates the number of bytes in the value. If you need a bigger storage, consider using MEDIUMTEXT instead.

An optional length M can be given for this type. If this is done, MariaDB creates the column as the smallest TEXT type large enough to hold values M characters long.

Currently, all MariaDB collations are of type PADSPACE, meaning that TEXT (as well as VARCHAR and CHAR values) are compared without regard for trailing spaces. This does not apply to the LIKE pattern-matching operator, which takes into account trailing spaces.

Before MariaDB 10.2.1, BLOB and TEXT columns could not be assigned a DEFAULT value. This restriction was lifted in MariaDB 10.2.1.

Examples

Trailing spaces:

CREATE TABLE strtest (d TEXT(10));
INSERT INTO strtest VALUES('Maria   ');

SELECT d='Maria',d='Maria   ' FROM strtest;
+-----------+--------------+
| d='Maria' | d='Maria   ' |
+-----------+--------------+
|         1 |            1 |
+-----------+--------------+

SELECT d LIKE 'Maria',d LIKE 'Maria   ' FROM strtest;
+----------------+-------------------+
| d LIKE 'Maria' | d LIKE 'Maria   ' |
+----------------+-------------------+
|              0 |                 1 |
+----------------+-------------------+

Difference between VARCHAR and TEXT

  • VARCHAR columns can be fully indexed. TEXT columns can only be indexed over a specified length.
  • Using TEXT or BLOB in a SELECT queries that uses temporary tables, for storing intermediate results, will force the temporary table to be disk based (using the Aria storage engine instead of the [memory-storage-engine|memory storage engine]], which is a bit slower. This is not that bad as the Aria storage engine caches the rows in memory. To get a benefit of this, one should ensure that the variable aria_pagecache_buffer_size variable is big enough to hold a majority of the row and index data for temporary tables.

For storage engine developers

  • Internally in the full length of the VARCHAR ciolumn is allocated inside each TABLE objects record[] structure. As there are 3 such buffers, each open table will 3 times max-length-to-store-varchar bytes of memory.
  • TEXT and BLOB columns are stored with a pointer (4 or 8 bytes) + a 1-4 byte length. The TEXT data is only stored once. This means that internally TEXT uses less memory for each open table but has instead the additional overhead that each TEXT object needs to be allocated & freed for each row access (with some caching in between).

See also

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