Collations essentially affect the string attribute comparisons. They specify both the character set encoding and the strategy that Manticore uses to compare strings when doing ORDER BY or GROUP BY with a string attribute involved.
String attributes are stored as is when indexing, and no character set or language information is attached to them. That's okay as long as Manticore only needs to store and return the strings to the calling application verbatim. But when you ask Manticore to sort by a string value, that request immediately becomes quite ambiguous.
First, single-byte (ASCII, or ISO-8859-1, or Windows-1251) strings need to be processed differently that the UTF-8 ones that may encode every character with a variable number of bytes. So we need to know what is the character set type to interpret the raw bytes as meaningful characters properly.
Second, we additionally need to know the language-specific string sorting rules. For instance, when sorting according to US rules in en_US locale, the accented character ï (small letter i with diaeresis) should be placed somewhere after z. However, when sorting with French rules and fr_FR locale in mind, it should be placed between i and j. And some other set of rules might choose to ignore accents at all, allowing ï and i to be mixed arbitrarily.
Third, but not least, we might need case-sensitive sorting in some scenarios and case-insensitive sorting in some others.
Collations combine all of the above: the character set, the language rules, and the case sensitivity. Manticore currently provides the following four collations.
libc_cilibc_csutf8_general_cibinary
The first two collations rely on several standard C library (libc) calls and can thus support any locale that is installed on your system. They provide case-insensitive (_ci) and case-sensitive (_cs) comparisons respectively. By default they will use C locale, effectively resorting to bytewise comparisons. To change that, you need to specify a different available locale using collation_libc_locale directive. The list of locales available on your system can usually be obtained with the locale command:
$ locale -a
C
en_AG
en_AU.utf8
en_BW.utf8
en_CA.utf8
en_DK.utf8
en_GB.utf8
en_HK.utf8
en_IE.utf8
en_IN
en_NG
en_NZ.utf8
en_PH.utf8
en_SG.utf8
en_US.utf8
en_ZA.utf8
en_ZW.utf8
es_ES
fr_FR
POSIX
ru_RU.utf8
ru_UA.utf8The specific list of the system locales may vary. Consult your OS documentation to install additional needed locales.
utf8_general_ci and binary locales are built-in into Manticore. The first one is a generic collation for UTF-8 data (without any so-called language tailoring); it should behave similar to utf8_general_ci collation in MySQL. The second one is a simple bytewise comparison.
Collation can be overridden via SQL on a per-session basis using SET collation_connection statement. All subsequent SQL queries will use this collation. Otherwise all queries will use the server default collation or as specified in collation_server configuration directive. Manticore currently defaults to libc_ci collation.
Collations affect all string attribute comparisons, including those within ORDER BY and GROUP BY, so differently ordered or grouped results can be returned depending on the collation chosen. Note that collations don't affect full-text searching, for that use charset_table
ALTER TABLE index {ADD|DROP} COLUMN column_name [{INTEGER|INT|BIGINT|FLOAT|BOOL|MULTI|MULTI64|JSON|STRING|TIMESTAMP}]It supports adding one attribute at a time for RT indexes. The supported attribute types are:
- int
- bigint
- float
- bool
- multi-valued
- multi-valued 64bit
- json
- string
- Querying an index is impossible (because of a write lock) while adding a column.
- Newly created attribute's values are set to 0.
ALTERwill not work for distributed indexes and indexes without any attributes.DROP COLUMNwill fail if an index has only one attribute.
- Example
mysql> desc rt;
+------------+-----------+
| Field | Type |
+------------+-----------+
| id | bigint |
| text | field |
| group_id | uint |
| date_added | timestamp |
+------------+-----------+
4 rows in set (0.01 sec)
mysql> alter table rt add column test integer;
Query OK, 0 rows affected (0.04 sec)
mysql> desc rt;
+------------+-----------+
| Field | Type |
+------------+-----------+
| id | bigint |
| text | field |
| group_id | uint |
| date_added | timestamp |
| test | uint |
+------------+-----------+
5 rows in set (0.00 sec)
mysql> alter table rt drop column group_id;
Query OK, 0 rows affected (0.01 sec)
mysql> desc rt;
+------------+-----------+
| Field | Type |
+------------+-----------+
| id | bigint |
| text | field |
| date_added | timestamp |
| test | uint |
+------------+-----------+
4 rows in set (0.00 sec)ALTER RTINDEX index RECONFIGUREALTER can also reconfigure an RT index in plain mode, so that new tokenization, morphology, and other text processing settings from the configuration file take effect on the newly INSERT-ed rows, while retaining the existing rows as they were. Internally, it forcibly saves the current RAM chunk as a new disk chunk, and adjusts the index header, so that the new rows are tokenized using the new rules.
- Example
mysql> show index rt settings;
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| settings | |
+---------------+-------+
1 row in set (0.00 sec)
mysql> alter rtindex rt reconfigure;
Query OK, 0 rows affected (0.00 sec)
mysql> show index rt settings;
+---------------+----------------------+
| Variable_name | Value |
+---------------+----------------------+
| settings | morphology = stem_en |
+---------------+----------------------+
1 row in set (0.00 sec)Returns the absolute value of the argument.
Returns the arctangent function of two arguments, expressed in radians.
BITDOT(mask, w0, w1, ...) returns the sum of products of an each bit of a mask multiplied with its weight. bit0*w0 + bit1*w1 + ...
Returns the smallest integer value greater or equal to the argument.
Returns the cosine of the argument.
Returns the CRC32 value of a string argument.
Returns the exponent of the argument (e=2.718... to the power of the argument).
Returns the N-th Fibonacci number, where N is the integer argument. That is, arguments of 0 and up will generate the values 0, 1, 1, 2, 3, 5, 8, 13 and so on. Note that the computations are done using 32-bit integer math and thus numbers 48th and up will be returned modulo 2\^32.
Returns the largest integer value lesser or equal to the argument.
GREATEST(attr_json.some_array) function takes JSON array as the argument, and returns the greatest value in that array. Also works for MVA.
Returns the result of an integer division of the first argument by the second argument. Both arguments must be of an integer type.
LEAST(attr_json.some_array) function takes JSON array as the argument, and returns the least value in that array. Also works for MVA.
Returns the natural logarithm of the argument (with the base of e=2.718...).
Returns the common logarithm of the argument (with the base of 10).
Returns the binary logarithm of the argument (with the base of 2).
Returns the bigger of two arguments.
Returns the smaller of two arguments.
Returns the first argument raised to the power of the second argument.
RAND(seed) function returns a random float between 0..1. Optional, an integer seed value can be specified.
Returns the sine of the argument.
Returns the square root of the argument.