Erlang (programming language)/Tutorials/ETS

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ETS local data storage

ETS is the erlang table storage system, which provides hash storage and access functions. ETS data is stored in a process as long as it is running. Here is a sample of how to use some simple functions in ETS

Sample program: test_ets.erl

-module(test_ets).
-compile(export_all).

start() -> start( mouse ).

start( Animal ) ->
	Kingdom = ets:new( 'magic',  [] ),
	% note: table is not square
	populate( Kingdom, [{micky,mouse}, {mini,mouse}, {goofy}] ),
	Member = ets:member( Kingdom, micky ),
	io:format( " member ~w ~n ", [ Member ] ),
	show_next_key( Kingdom, micky ),
	find_animal( Kingdom, Animal ).
	
show_next_key( _Kingdom, '$end_of_table' ) -> done;
show_next_key( Kingdom,  Key) ->
	Next = ets:next( Kingdom, Key ),
	io:format( " next ~w ~n ", [ Next ] ),
	show_next_key( Kingdom, Next ).

populate( _Kingdom, [] ) -> {done,start};
populate( Kingdom, [H | T] ) ->
		ets:insert( Kingdom, H ),
		populate( Kingdom, T ).
	
find_animal( Kingdom, Animal ) ->
	ets:match( Kingdom, { '$1', Animal } ).

% ==============
% sample output
% ==============
% 53> test_ets:start().
% member true 
%  next mini 
%  next goofy 
%  next '$end_of_table' 
%  [[mini],[micky]]

Advanced options

There are a number of options for ets data.

Data structure options include: set, ordered set, bag, and duplicate bag. A set has only unique keys and values. An sorted version of set exists. A bag can have duplicate keys. A duplicate bag can have duplicate keys and values.

set           [{zod, alice},{smith, joe}]
ordered set   [{smith, joe},{zod, alice}]
bag           [{smith, joe},{smith, ann}]
duplicate bag [{smith, joe},{smith, joe]]

Access options include: private, protected, and public. Private ets data is limited to the owning process. Protected ets tables are readable by other processes. Public ets tables have read and write access by other processes.