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.. -*- rst -*-
.. highlightlang:: none
Tables
======
Summary
-------
Table in Groonga manages relation between ID and key. Groonga provides
four table types. They are ``TABLE_NO_KEY``, ``TABLE_HASH_KEY``,
``TABLE_PAT_KEY`` and ``TABLE_DAT_KEY``.
All tables except ``TABLE_NO_KEY`` provides both fast ID search by key
and fast key search by ID. ``TABLE_NO_KEY`` doesn't support
key. ``TABLE_NO_KEY`` only manages ID. So ``TABLE_NO_KEY`` doesn't
provides ID search and key search.
Characteristics
---------------
Here is a chracteristic table of all tables in Groonga. (``TABLE_``
prefix is omitted in the table.)
.. list-table:: Characteristics of all tables
:header-rows: 1
* - Item
- ``NO_KEY``
- ``HASH_KEY``
- ``PAT_KEY``
- ``DAT_KEY``
* - Data structure
- Array
- Hash table
- Patricia trie
- Double array trie
* - ID support
- o
- o
- o
- o
* - Key support
- x
- o
- o
- o
* - Value support
- o
- o
- o
- x
* - Key -> ID speed
* o: fast
* x: slow
- \-
- oo
- x
- o
* - Update speed
* o: fast
* x: slow
- ooo
- o
- o
- x
* - Size
* o: small
* x: large
- ooo
- o
- oo
- x
* - Key update
- \-
- x
- x
- o
* - Common prefix search
- \-
- x
- o
- o
* - Predictive search
- \-
- x
- o
- o
* - Range search
- \-
- x
- o
- o
* - The maximum one key size
- \-
- 4KiB
- 4KiB
- 4KiB
* - The maximum total size of keys
- \-
- 4GiB or 1TiB (by specifying ``KEY_LARGE`` flag to
:ref:`table-create-flags`)
- 4GiB
- 4GiB
* - The maximum number of records
- 1,073,741,815 (2 :sup:`30` - 9)
- 536,870,912 (2 :sup:`29`)
- 1,073,741,823 (2 :sup:`30` - 1)
- 268,435,455 (2 :sup:`28` - 1)
.. _table-no-key:
``TABLE_NO_KEY``
^^^^^^^^^^^^^^^^
``TABLE_NO_KEY`` is very fast and very small but it doesn't support
key. ``TABLE_NO_KEY`` is a only table that doesn't support key.
You cannot use ``TABLE_NO_KEY`` for lexicon for fulltext search
because lexicon stores tokens as key. ``TABLE_NO_KEY`` is useful for
no key records such as log.
.. _table-hash-key:
``TABLE_HASH_KEY``
^^^^^^^^^^^^^^^^^^
``TABLE_HASH_KEY`` is fast but it doesn't support advanced search
functions such as common prefix search and predictive search.
``TABLE_HASH_KEY`` is useful for index for exact search such as tag
search.
.. _table-pat-key:
``TABLE_PAT_KEY``
^^^^^^^^^^^^^^^^^
``TABLE_PAT_KEY`` is small and supports advanced search functions.
``TABLE_PAT_KEY`` is useful for lexicon for fulltext search and
index for range search.
.. _table-dat-key:
``TABLE_DAT_KEY``
^^^^^^^^^^^^^^^^^
``TABLE_DAT_KEY`` is fast and supports key update but it is large. It
is not suitable for storing many records. ``TABLE_DAT_KEY`` is a only
table that supports key update.
``TABLE_DAT_KEY`` is used in Groonga database. Groonga database needs
to convert object name such as ``ShortText``, ``TokenBigram`` and
table names to object ID. And Groonga database needs to rename object
name. Those features are implemented by ``TABLE_DAT_KEY``. The number
of objects is small. So large data size demerit of ``TABLE_DAT_KEY``
can be ignored.
Record ID
---------
Record ID is assigned automatically. You cannot assign record ID.
Record ID of deleted record may be reused.
Valid record ID range is between 1 and 1073741823. (1 and 1073741823
are valid IDs.)
Persistent table and temporary table
------------------------------------
Table is persistent table or temporary table.
Persistent table
^^^^^^^^^^^^^^^^
Persistent table is named and registered to database. Records in
persistent table aren't deleted after closing table or
database.
Persistent table can be created by
:doc:`/reference/commands/table_create` command.
Temporary table
^^^^^^^^^^^^^^^
Temporary table is anonymous. Records in temporary table are deleted
after closing table. Temporary table is used to store search result,
sort result, group (drilldown) result and so on. ``TABLE_HASH_KEY`` is
used for search result and group result. ``TABLE_NO_KEY`` is used for
sort result.
Limitations
-----------
The max number of records is 268435455. You cannot add 268435456 or
more records in a table.
The max number of a key size is 4096byte. You cannot use 4097byte or
larger key. You can use column instead of key for 4097byte or larger
size data. ``Text`` and ``LargeText`` types supports 4097byte or
larger size data.
The max number of total key size is 4GiB. You need to split a table,
split a database (sharding) or reduce each key size to handle 4GiB or
more larger total key size.
See also
--------
* :doc:`/reference/commands/table_create`
|
