Модуль merger
The four functions for creating a merger object instance are:
- merger.new_tuple_source(),
- merger.new_buffer_source(),
- merger.new_table_source,
- merger.new(merger_source…).
The methods for using a merger object are:
-
merger.
new_tuple_source
(gen, param, state)¶ Create a new merger instance from a tuple source.
A tuple source just returns one tuple.
The generator function
gen()
allows creation of multiple tuples via an iterator.The
gen()
function should return:- state, tuple each time it is called and a new tuple is available,
- nil when no more tuples are available.
Параметры: - gen – function for iteratively returning tuples
- param – parameter for the gen function
возвращает: merger-object a merger object
Example: see merger_object:pairs() method.
-
merger.
new_buffer_source
(gen, param, state)¶ Create a new merger instance from a buffer source.
Parameters and return: same as for merger.new_tuple_source.
To set up a buffer, or a series of buffers, use the buffer module.
-
merger.
new_table_source
(gen, param, state)¶ Create a new merger instance from a table source.
Parameters and return: same as for merger.new_tuple_source.
Example: see merger_object:select() method.
-
merger.
new
(key_def, sources, options)¶ Create a new merger instance from a merger source.
A merger source is created from a key_def object and a set of (tuple or buffer or table or merger) sources. It performs a kind of merge sort. It chooses a source with a minimal / maximal tuple on each step, consumes a tuple from this source, and repeats.
Параметры: - key_def – object created with
key_def
- source – parameter for the
gen()
function - options –
reverse=true
if descending, false or nil if ascending
возвращает: merger-object a merger object
A
key_def
can be cached across requests with the same ordering rules (typically these would be requests accessing the same space).Example: see merger_object:pairs() method.
- key_def – object created with
-
object
merger_object
¶ A merger object is an object returned by:
- merger.new_tuple_source() or
- merger.new_buffer_source() or
- merger.new_table_source or
- merger.new(merger_source…).
It has methods:
-
merger_object:
select
([buffer[, limit]])¶ Access the contents of a merger object with familiar
select
syntax.Параметры: - buffer – as in
net.box
client conn:select method - limit – as in
net.box
client conn:select method
возвращает: a table of tuples, similar to what
select
would returnExample with new_table_source():
-- Source via new_table_source, simple generator function -- tarantool> s:select() -- --- -- - - [100] -- - [200] -- ... merger=require('merger') k=0 function merger_function(param) k = k + 1 if param[k] == nil then return nil end return box.NULL, param[k] end chunks={} chunks[1] = {{100}} chunks[2] = {{200}} chunks[3] = nil s = merger.new_table_source(merger_function, chunks) s:select()
- buffer – as in
-
merger_object:
pairs
()¶ The
pairs()
method (or the equivalentipairs() alias
method) returns a luafun iterator. It is a Lua iterator, but also provides a set of handy methods to operate in functional style.Параметры: - tuple (
table
) – tuple or Lua table with field contents
возвращает: the tuples that can be found with a standard
pairs()
functionExample with new_tuple_source():
-- Source via new_tuple_source, from a space of tables -- The result will look like this: -- tarantool> so:pairs():totable() -- --- -- - - [100] -- - [200] -- ... merger = require('merger') box.schema.space.create('s') box.space.s:create_index('i') box.space.s:insert({100}) box.space.s:insert({200}) so = merger.new_tuple_source(box.space.s:pairs()) so:pairs():totable()
Example with two mergers:
-- Source via key_def, and table data -- Create the key_def object merger = require('merger') key_def_lib = require('key_def') key_def = key_def_lib.new({{ fieldno = 1, type = 'string', }}) -- Create the table source data = {{'a'}, {'b'}, {'c'}} source = merger.new_source_fromtable(data) i1 = merger.new(key_def, {source}):pairs() i2 = merger.new(key_def, {source}):pairs() -- t1 will be 'a' (tuple 1 from merger 1) t1 = i1:head():totable() -- t3 will be 'c' (tuple 3 from merger 2) t3 = i2:head():totable() -- t2 will be 'b' (tuple 2 from merger 1) t2 = i1:head():totable() -- i1:is_null() will be true (merger 1 ends) i1:is_null() -- i2:is_null() will be true (merger 2 ends) i2:is_null()
More examples:
See https://github.com/Totktonada/tarantool-merger-examples which, in addition to discussing the merger API in detail, shows Lua code for handling many more situations than are in this manual’s brief examples.
- tuple (