Модель данных¶

Lua vs MsgPack¶

In Lua, a nil type has only one possible value, also called nil (displayed as null on Tarantool’s command line, since the output is in the YAML format). Nils may be compared to values of any types with == (is-equal) or ~= (is-not-equal), but other operations will not work. Nils may not be used in Lua tables; the workaround is to use msgpack.NULL

A boolean is either true or false.

A string is a variable-length sequence of bytes, usually represented with alphanumeric characters inside single quotes. In both Lua and MsgPack, strings are treated as binary data, with no attempts to determine a string’s character set or to perform any string conversion. So, string sorting and comparison are done byte-by-byte, without any special collation rules applied. (Example: numbers are ordered by their point on the number line, so 2345 is greater than 500; meanwhile, strings are ordered by the encoding of the first byte, then the encoding of the second byte, and so on, so „2345“ is less than „500“.)

In Lua, a number is double-precision floating-point, but Tarantool allows both integer and floating-point values. Tarantool will try to store a Lua number as floating-point if the value contains a decimal point or is very large (greater than 100 billion = 1e14), otherwise Tarantool will store it as an integer. To ensure that even very large numbers are stored as integers, use the tonumber64 function, or the LL (Long Long) suffix, or the ULL (Unsigned Long Long) suffix. Here are examples of numbers using regular notation, exponential notation, the ULL suffix and the tonumber64 function: -55, -2.7e+20, 100000000000000ULL, tonumber64('18446744073709551615').

Lua tables with string keys are stored as MsgPack maps; Lua tables with integer keys starting with 1 – as MsgPack arrays. Nils may not be used in Lua tables; the workaround is to use msgpack.NULL

A tuple is a light reference to a MsgPack array stored in the database. It is a special type (cdata) to avoid conversion to a Lua table on retrieval. A few functions may return tables with multiple tuples. For more tuple examples, see box.tuple.

Indexed field types¶

Indexes restrict values which Tarantool’s MsgPack may contain. This is why, for example, „NUM“ is a separate indexed field type, compared to ‘integer’ data type in MsgPack: they both store ‘integer’ values, but a „NUM“ index contains either real or integer values and a MsgPack ‘integer’ contains only integer values.

Here’s how Tarantool indexed field types correspond to MsgPack data types.

Data operations¶

The basic data operations supported in Tarantool are:

• one data-retrieval operation (SELECT), and
• five data-manipulation operations (INSERT, UPDATE, UPSERT, DELETE, REPLACE).

All of them are implemented as functions in box.space submodule.

Examples

• INSERT: Add a new tuple to space „tester“.

  The first field, field[1], will be 999 (MsgPack type is integer).

  The second field, field[2], will be „Taranto“ (MsgPack type is string).

  tarantool> box.space.tester:insert{999, 'Taranto'}
  

• UPDATE: Update the tuple, changing field field[2].

  The clause «{999}», which has the value to look up in the index of the tuple’s primary-key field, is mandatory, because update() requests must always have a clause that specifies a unique key, which in this case is field[1].

  The clause «{{„=“, 2, „Tarantino“}}» specifies that assignment will happen to field[2] with the new value.

  tarantool> box.space.tester:update({999}, {{'=', 2, 'Tarantino'}})
  

• UPSERT: Upsert the tuple, changing field field[2] again.

  The syntax of upsert() is similar to the syntax of update(). However, the execution logic of these two requests is different. UPSERT is either UPDATE or INSERT, depending on the database’s state. Also, UPSERT execution is postponed after transaction commit, so, unlike update(), upsert() doesn’t return data back.

  tarantool> box.space.tester:upsert({999,''}, {{'=', 2, 'Tarantism'}})
  

• REPLACE: Replace the tuple, adding a new field.

  This is also possible with the update() request, but the update() request is usually more complicated.

  tarantool> box.space.tester:replace{999, 'Tarantella', 'Tarantula'}
  

• SELECT: Retrieve the tuple.

  The clause «{999}» is still mandatory, although it does not have to mention the primary key.

  tarantool> box.space.tester:select{999}
  

• DELETE: Delete the tuple.

  In this example, we identify the primary-key field.

  tarantool> box.space.tester:delete{999}
  

All the functions operate on tuples and accept only unique key values. So, the number of tuples affected is always 0 or 1, since the keys are unique.

Операции с индексами¶

Index operations are automatic: if a data-manipulation request changes a tuple, then it also changes the index keys defined for the tuple.

The simple index-creation operation that we’ve illustrated before is:

:samp:`box.space.{имя-пространства}:create_index('{имя-индекса}')`

This creates a unique TREE index on the first field of all tuples (often called «Field#1»), which is assumed to be numeric.

The simple SELECT request that we’ve illustrated before is:

:extsamp:`box.space.{*{имя-пространства}*}:select({*{значение}*})`

This looks for a single tuple via the first index. Since the first index is always unique, the maximum number of returned tuples will be: one.

The following SELECT variations exist:

1. Помимо условия равенства, при поиске могут использоваться и другие условия сравнения.

   box.space.space-name:select(value, {iterator = 'GT'})
   

   The comparison operators are LT, LE, EQ, REQ, GE, GT (for «less than», «less than or equal», «equal», «reversed equal», «greater than or equal», «greater than» respectively). Comparisons make sense if and only if the index type is ‘TREE“.

   Этот вариант поиска может вернуть более одного кортежа. В таком случае кортежи будут отсортированы в порядке убывания по ключу (если использовался оператор LT, LE или REQ), либо в порядке возрастания (во всех остальных случаях).

2. Поиск может производиться по вторичному индексу.

   box.space.space-name.index.index-name:select(value)
   

   При поиске по первичному индексу имя индекса можно не указывать. При поиске же по вторичному индексу имя индекса указывать необходимо.

3. Поиск может производиться как по всему ключу, так и по его частям.

   -- Suppose an index has two parts
   tarantool> box.space.space-name.index.index-name.parts
   ---
   - - type: NUM
       fieldno: 1
     - type: STR
       fieldno: 2
   ...
   -- Suppose the space has three tuples
   box.space.space-name:select()
   ---
   - - [1, 'A']
     - [1, 'B']
     - [2, '']
   ...
   

4. The search may be for all fields, using a table for the value:

   box.space.space-name:select({1, 'A'})
   

   Либо же по одному полю (в этом случае используется таблица или скалярное значение):

   box.space.space-name:select(1)
   

   In the second case, the result will be two tuples: {1, 'A'} and {1, 'B'}.

   You can specify even zero fields, causing all three tuples to be returned. (Notice that partial key searches are available only in TREE indexes.)

Examples

• Пример работы с BITSET-индексом:

  tarantool> box.schema.space.create('bitset_example')
  tarantool> box.space.bitset_example:create_index('primary')
  tarantool> box.space.bitset_example:create_index('bitset',{unique=false,type='BITSET', parts={2,'NUM'}})
  tarantool> box.space.bitset_example:insert{1,1}
  tarantool> box.space.bitset_example:insert{2,4}
  tarantool> box.space.bitset_example:insert{3,7}
  tarantool> box.space.bitset_example:insert{4,3}
  tarantool> box.space.bitset_example.index.bitset:select(2, {iterator='BITS_ANY_SET'})
  

  Мы получим следующий результат:

  ---
  - - [3, 7]
    - [4, 3]
  ...
  

  поскольку (7 AND 2) не равно 0 и (3 AND 2) не равно 0.

• Пример работы с RTREE-индексом:

  tarantool> box.schema.space.create('rtree_example')
  tarantool> box.space.rtree_example:create_index('primary')
  tarantool> box.space.rtree_example:create_index('rtree',{unique=false,type='RTREE', parts={2,'ARRAY'}})
  tarantool> box.space.rtree_example:insert{1, {3, 5, 9, 10}}
  tarantool> box.space.rtree_example:insert{2, {10, 11}}
  tarantool> box.space.rtree_example.index.rtree:select({4, 7, 5, 9}, {iterator = 'GT'})
  

  Мы получим следующий результат:

  ---
  - - [1, [3, 5, 9, 10]]
  ...
  

  because a rectangle whose corners are at coordinates 4,7,5,9 is entirely within a rectangle whose corners are at coordinates 3,5,9,10.

Additionally, there exist index iterator operations. They can only be used with code in Lua and C/C++. Index iterators are for traversing indexes one key at a time, taking advantage of features that are specific to an index type, for example evaluating Boolean expressions when traversing BITSET indexes, or going in descending order when traversing TREE indexes.

See also other index operations like alter() and drop() in reference for box.index submodule.

Complexity factors¶

In reference for box.space and box.index submodules, there are notes about which complexity factors might affect the resource usage of each function.