Why Use a VARCHAR Field Instead of TEXT in MySQL
James Reed
Infrastructure Engineer · Leapcell

Background
When storing a segment of serialized data of uncertain length in a database, many people design the field as VARCHAR(2000)
in the table schema.
But if the length is uncertain, why not use the TEXT
type instead? Some say: TEXT affects query performance.
Is that really the reason? This article will explore that:
What is TEXT
TEXT
is a variable-length data type in MySQL, including TINYTEXT
, TEXT
, MEDIUMTEXT
, and LONGTEXT
. They are typically used to store large amounts of textual data, with the following storage limits:
TINYTEXT
: 0 - 255 bytesTEXT
: 0 - 65,535 bytesMEDIUMTEXT
: 0 - 16,777,215 bytesLONGTEXT
: 0 - 4,294,967,295 bytes
How TEXT is Stored
Each BLOB
or TEXT
value is represented internally by a separately allocated object, whereas other data types have storage space allocated once per column when the table is opened.
When storing string-type data, InnoDB encodes fixed-length fields of 768 bytes or more as variable-length fields and stores them in overflow pages. Data smaller than 768 bytes is stored directly in the data row. Therefore, when using other string types, avoid storing data that is 768 bytes or larger.
Limitations of TEXT
TEXT
cannot have a default value.- When indexing a
TEXT
field, a prefix length must be specified. - When comparing index entries, trailing spaces are padded. If a unique index is required, this can lead to duplicate key errors.
TEXT
fields may be particularly long. When sorting, only the firstmax_sort_length
bytes (default is 1024) are used. This value can be adjusted by modifying the variable:
-- View max_sort_length SELECT @@max_sort_length; -- Set max_sort_length SET max_sort_length = 2048;
-
When processed with temporary tables, the server will use tables on disk rather than in memory, because the
MEMORY
storage engine does not supportTEXT
type. -
The size of a
TEXT
object is determined by its type, but the actual transferable maximum size is limited by the available content and communication buffer size. This can be adjusted by changing themax_allowed_packet
variable:
-- View max_allowed_packet SELECT @@max_allowed_packet; -- Set max_allowed_packet SET max_allowed_packet = 67108864;
Conclusion
TEXT
can be used to store large amounts of textual data. However, for several reasons, it is not recommended to use TEXT
:
Performance Issues
TEXT
is represented internally as a separately allocated object, requiring additional operations and resource consumption during storage and retrieval.- If a
TEXT
field is especially large, reading it can increase memory pressure, impacting overall system performance. - The
MEMORY
storage engine does not supportTEXT
, so when temporary tables are used, data fromTEXT
fields will be read from disk rather than directly from memory.
Indexing Limitations
Indexes can improve query performance, but indexing TEXT
fields comes with certain restrictions and complexity:
- When used as a unique index, it may result in duplicate key errors.
- Creating full-text indexes requires additional computation and space to maintain. If the
TEXT
field is too large, it may negatively impact performance.
Therefore, it's advisable to avoid using the TEXT
type in table schema design. If it must be used, consider the following approaches:
- Separate
TEXT
fields into independent tables, linking to the main table via primary key. - Avoid reading
TEXT
fields unless necessary — for example, do not useSELECT *
. - For large fields, consider storing them in OSS (Object Storage Service).
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