This module is an interface to the Erlang built-in term storage BIFs.
These provide the ability to store very large quantities of data in
an Erlang runtime system, and to have constant access time to the
data. (In the case of ordered_set
, see below, access time is
proportional to the logarithm of the number of objects stored).
Data is organized as a set of dynamic tables, which can store tuples. Each table is created by a process. When the process terminates, the table is automatically destroyed. Every table has access rights set at creation.
Tables are divided into four different types, set
,
ordered_set
, bag
and duplicate_bag
.
A set
or ordered_set
table can only have one object
associated with each key. A bag
or duplicate_bag
can
have many objects associated with each key.
The number of tables stored at one Erlang node is limited.
The current default limit is approximately 1400 tables. The upper
limit can be increased by setting the environment variable
ERL_MAX_ETS_TABLES
before starting the Erlang runtime system
(i.e. with the -env
option to erl
/werl
).
The actual limit may be slightly higher than the one specified, but
never lower.
Note that there is no automatic garbage collection for tables.
Even if there are no references to a table from any process, it will
not automatically be destroyed unless the owner process terminates.
It can be destroyed explicitly by using delete/1
.
Some implementation details:
safe_fixtable/2
function can
be used to guarantee that a sequence of first/1
and
next/2
calls will traverse the table without errors even if
another process (or the same process) simultaneously deletes or
inserts objects in the table.
'$end_of_table'
should not be used as a key since this
atom is used to mark the end of the table when using
first
/next
.
In general, the functions below will exit with reason badarg
if
any argument is of the wrong format, or if the table identifier is
invalid.
The type tid()
is used to denote a table identifier. Note that
the internal structure of this type is implementation-specific.
Types:
Tab = tid() | atom()
Returns a list of all tables at the node. Named tables are given by their names, unnamed tables are given by their table identifiers.
Types:
Tab = tid() | atom()
Deletes the entire table Tab
.
Types:
Tab = tid() | atom()
Key = term()
Deletes all objects with the key Key
from the table
Tab
.
delete_all_objects(Tab) -> true
Types:
Tab = tid() | atom()
Delete all objects in the ETS table Tab
. The
deletion is atomic.
delete_object(Tab,Object) -> true
Types:
Tab = tid() | atom()
Object = tuple()
Delete the exact object Object
from the ETS table,
leaving objects with the same key but other differences
(useful for type bag
).
file2tab(Filename) -> {ok,Tab} | {error,Reason}
Types:
Filename = string() | atom()
Tab = tid() | atom()
Reason = term()
Reads a file produced by tab2file/2
and creates the
corresponding table Tab
.
first(Tab) -> Key | '$end_of_table'
Types:
Tab = tid() | atom()
Key = term()
Returns the first key Key
in the table Tab
.
If the table is of the ordered_set
type, the first key
in Erlang term order will be returned. If the table is of any
other type, the first key according to the table's internal
order will be returned. If the table is empty,
'$end_of_table'
will be returned.
Use next/2
to find subsequent keys in the table.
fixtable(Tab, true|false) -> true | false
Types:
Tab = tid() | atom()
The function is retained for backwards compatibility only.
Use |
Fixes a table for safe traversal. The function is primarily used by the Mnesia DBMS to implement functions which allow write operations in a table, although the table is in the process of being copied to disk or to another node. It does not keep track of when and how tables are fixed.
foldl(Function, Acc0, Tab) -> Acc1
Types:
Function = fun(A, AccIn) -> AccOut
Tab = tid() | atom()
Acc0 = Acc1 = AccIn = AccOut = term()
Acc0
is returned if the table is empty.
This function is similar to lists:foldl/3
. The order in
which the elements of the table are traversed is unspecified,
except for tables of type ordered_set
, for which they
are traversed first to last.
foldr(Function, Acc0, Tab) -> Acc1
Types:
Function = fun(A, AccIn) -> AccOut
Tab = tid() | atom()
Acc0 = Acc1 = AccIn = AccOut = term()
Acc0
is returned if the table is empty.
This function is similar to lists:foldr/3
. The order in
which the elements of the table are traversed is unspecified,
except for tables of type ordered_set
, for which they
are traversed last to first.
from_dets(Tab, DetsTab) -> Tab
Types:
Tab = tid() | atom()
DetsTab = atom()
Fills an already created ETS table with the objects in the
already opened DETS table named DetsTab
. The ETS table
is emptied before the objects are inserted.
fun2ms(LiteralFun) -> MatchSpec
Types:
LiteralFun = fun() literal
MatchSpec = term()
Pseudo function that by means of a parse_transform
translates the literal fun()
typed as parameter in
the function call to a match specification as described in
the match_spec
manual of ERTS
users guide.
(with literal I mean that the fun()
needs to
textually be written as the parameter of the function, it
cannot be held in a variable which in turn is passed to the
function).
The parse transform is implemented in the module
ms_transform
and the source must include the
file ms_transform.hrl
in stdlib
for this
pseudo function to work. Failing to include the hrl file in
the source will result in a runtime error, not a compile
time dito. The include file is easiest included by adding
the line
-include_lib("stdlib/include/ms_transform.hrl").
to
the source file.
The fun()
is very restricted, it can take only a
single parameter (the object to match), a sole variable or a
tuple. It needs to use the is_
XXX guard tests and one
cannot use language constructs that have no representation
in a match_spec (like if
, case
,
recieve
etc). The return value from the fun will be
the return value of the resulting match_spec.
Example:
2> ets:fun2ms(fun({M,N}) when N > 3 -> M end). [{{'$1','$2'},[{'>','$2',3}],['$1']}]
Variables from the environment can be imported, so that this works:
2> X=3. 3 3> ets:fun2ms(fun({M,N}) when N > X -> M end). [{{'$1','$2'},[{'>','$2',{const,3}}],['$1']}]
The imported variables will be replaced by match_spec
const
expressions, which is consistent with the
static scoping for erlang fun()
's. Local or global
function calls can not be in the guard or body of the fun
however. Calls to builtin match_spec functions of course is
allowed:
4> ets:fun2ms(fun({M,N}) when N > X, is_atomm(M) -> M end). Error: fun containing local erlang function calls ('is_atomm' called in guard) cannot be translated into match_spec {error,transform_error} 5> ets:fun2ms(fun({M,N}) when N > X, is_atom(M) -> M end). [{{'$1','$2'},[{'>','$2',{const,3}},{is_atom,'$1'}],['$1']}]
As you can see by the example, the function can be called from
the shell too. The fun()
needs to be literally in the
call when used from the shell as well. Other means than the
parse_transform are used in the shell case, but more or less
the same restrictions apply (the exception beeing records,
as they are not handled by the shell).
If the parse_transform is not applied to a module which calls this
pseudo function, the call will fail in runtime (with a
|
More information is provided by the ms_transform
manual page in stdlib
.
Displays information about all ETS tables on tty.
Types:
Tab = tid() | atom()
Browses the table Tab
on tty.
info(Tab) -> [{Item,Value}] | undefined
Types:
Tab = tid() | atom()
Item, Value - see below
Returns information about the table Tab
as a list of
{Item,Value}
tuples:
Item=memory, Value=int()
Item=owner, Value=pid()
Item=name, Value=atom()
Item=size, Value=int()
Item=node, Value=atom()
Item=named_table, Value=true|false
Item=type, Value=set|ordered_set|bag|duplicate_bag
Item=keypos, Value=int()
Item=protection, Value=public|protected|private
info(Tab, Item) -> Value | undefined
Types:
Tab = tid() | atom()
Item, Value - see below
Returns the information associated with Item
for
the table Tab
. In addition to the {Item,Value}
pairs defined for info/1
, the following items are
allowed:
Item=fixed, Value=true|false
Item=safe_fixed, Value={FirstFixed,Info}|false
safe_fixtable/2
,
the call returns a tuple where FirstFixed
is the time
when the table was first fixed by a process, which may or may
not be one of the processes it is fixed by right now.Info
is a possibly empty lists of tuples
{Pid,RefCount}
, one tuple for every process the table is
fixed by right now. RefCount
is the value of the
reference counter, keeping track of how many times the table
has been fixed by the process.false
.init_table(Name, InitFun) -> true
Types:
Name = atom()
InitFun = fun(Arg) -> Res
Arg = read | close
Res = end_of_input | {[object()], InitFun} | term()
Replaces the existing objects of the table Tab
with
objects created by calling the input function InitFun
,
see below. This function is provided for compatibility with
the DETS module, it's not more efficient than filling a table
by using ets:insert/2
.
When called with the argument read
the function
InitFun
is assumed to return end_of_input
when
there is no more input, or {Objects, Fun}
, where
Objects
is a list of objects and Fun
is a new
input function. Any other value Value is returned as an error
{error, {init_fun, Value}}
. Each input function will be
called exactly once, and should an error occur, the last
function is called with the argument close
, the reply
of which is ignored.
If the type of the table is set
and there is more
than one object with a given key, one of the objects is
chosen. This is not necessarily the last object with the given
key in the sequence of objects returned by the input
functions. This holds also for duplicated
objects stored in tables of type duplicate_bag
.
insert(Tab, ObjectOrObjects) -> true
Types:
Tab = tid() | atom()
ObjectOrObjects = tuple() | [tuple()]
Inserts the object or all of the objects in the list
ObjectOrObjects
into the table Tab
. If there
already exists an object with the same key as one of the
objects, and the table is a set
or ordered_set
table, the old object will be replaced. If the list contains
more than one object with the same key and the table is a
set/ordered_set
, one will be inserted, which one is
not defined.
insert_new(Tab, ObjectOrObjects) -> bool()
Types:
Tab = tid() | atom()
ObjectOrObjects = tuple() | [tuple()]
This function works exactly like insert/2, with the
exception that instead of overwriting objects with the same
key (in the case of sets or ordered_sets) or adding more
objects with keys already existing in the table (in the case
of bags and duplicate_bags), it simly returns false
. If
ObjectOrObjects
is a list, the function checks
every key prior to inseting anything. Nothing will be
inserted if not all keys present in the list are
absent from the table.
last(Tab) -> Key | '$end_of_table'
Types:
Tab = tid() | atom()
Key = term()
Returns the last key Key
according to Erlang term order
in the table Tab
of the ordered_set
type. If
the table is of any other type, the function is synonymous to
first/2
. If the table is empty, '$end_of_table'
is
returned.
Use prev/2
to find preceding keys in the table.
Types:
Tab = tid() | atom()
Key = term()
Object = tuple()
Returns a list of all objects with the key Key
in
the table Tab
.
If the table is of type set
or ordered_set
,
the function returns either the empty list or a list with one
element, as there cannot be more than one object with the same
key. If the table is of type bag
or duplicate_bag
,
the function returns a list of arbitrary length.
Note that the time order of object insertions is preserved; The first object inserted with the given key will be first in the resulting list, and so on.
Insert and look-up times in tables of type set
, bag
and duplicate_bag
are constant, regardless of the size of
the table. For the ordered_set
data-type, time is
proportional to the (binary) logarithm of the number of objects.
lookup_element(Tab, Key, Pos) -> Elem
Types:
Tab = tid() | atom()
Key = term()
Pos = int()
Elem = term() | [term()]
If the table Tab
is of type set
or
ordered_set
, the function returns the Pos
:th
element of the object with the key Key
.
If the table is of type bag
or duplicate_bag
,
the functions returns a list with the Pos
:th element of
every object with the key Key
.
If no object with the key Key
exists, the function will
exit with reason badarg
.
match(Tab, Pattern) -> [Match]
Types:
Tab = tid() | atom()
Pattern = tuple()
Match = [term()]
Matches the objects in the table Tab
against the pattern
Pattern
.
A pattern is a term that may contain:
'_'
which matches any Erlang term, and
'$N'
where N
=0,1,...
The function returns a list with one element for each matching object, where each element is an ordered list of pattern variable bindings. An example:
> ets:match(T, '$1'). % Matches every object in the table [{rufsen,dog,7},{brunte,horse,5},{ludde,dog,5}] > ets:match(T, {'_',dog,'$1'}). [[7],[5]] > ets:match(T, {'_',cow,'$1'}). []
If the key is specified in the pattern, the match is very efficient. If the key is not specified, i.e. if it is a variable or an underscore, the entire table must be searched. The search time can be substantial if the table is very large.
On tables of the ordered_set
type, the result is in the
same order as in a first/next
traversal.
match(Tab, Pattern, Limit) -> {[Match],Continuation} | '$end_of_table'
Types:
Tab = tid() | atom()
Pattern = tuple()
Match = [term()]
Continuation = term()
Works like ets:match/2
but only returns a limited
(Limit
) number of matching objects. The
Continuation
term can then be used in subsequent calls
to ets:match/1
to get the next chunk of matching
objects. This is a space efficient way to work on objects in a
table which is still faster than traversing the table object
by object using ets:first/1
and ets:next/1
.
'$end_of_table'
is returned if the table is empty.
match(Continuation) -> {[Match],Continuation} | '$end_of_table'
Types:
Match = [term()]
Continuation = term()
Continues a match started with ets:match/3
. The next
chunk of the size given in the initial ets:match/3
call is returned together with a new Continuation
that can be used in subsequent calls to this function.
'$end_of_table' is returned when there are no more objects in the table.
match_delete(Tab, Pattern) -> true
Types:
Tab = tid() | atom()
Pattern = tuple()
Deletes all objects which match the pattern Pattern
from
the table Tab
. See match/2
for a description of
patterns.
match_object(Tab, Pattern) -> [Object]
Types:
Tab = tid() | atom()
Pattern = Object = tuple()
Matches the objects in the table Tab
against the pattern
Pattern
. See match/2
for a description of patterns.
The function returns a list of all objects which match the pattern.
If the key is specified in the pattern, the match is very efficient. If the key is not specified, i.e. if it is a variable or an underscore, the entire table must be searched. The search time can be substantial if the table is very large.
On tables of the ordered_set
type, the result is in the
same order as in a first/next
traversal.
match_object(Tab, Pattern, Limit) -> {[Match],Continuation} | '$end_of_table'
Types:
Tab = tid() | atom()
Pattern = tuple()
Match = [term()]
Continuation = term()
Works like ets:match_object/2
but only returns a limited
(Limit
) number of matching objects. The
Continuation
term can then be used in subsequent calls
to ets:match_object/1
to get the next chunk of matching
objects. This is a space efficient way to work on objects in a
table which is still faster than traversing the table object
by object using ets:first/1
and ets:next/1
.
'$end_of_table'
is returned if the table is empty.
match_object(Continuation) -> {[Match],Continuation} | '$end_of_table'
Types:
Match = [term()]
Continuation = term()
Continues a match started with
ets:match_object/3
. The next
chunk of the size given in the initial ets:match_object/3
call is returned together with a new Continuation
that can be used in subsequent calls to this function.
'$end_of_table' is returned when there are no more objects in the table.
member(Tab, Key) -> true | false
Types:
Tab = tid() | atom()
Key = term()
Works like lookup/2, but does not return the objects. The
function returns true
if one or more elements in the
table has the key Key
, false
otherwise.
Types:
Name = atom()
Options = [Option]
Option = Type | Access | named_table | {keypos,Pos}
Type = set | ordered_set | bag | duplicate_bag
Access = public | protected | private
Pos = int()
Creates a new table and returns a table identifier which can be used in subsequent operations. The table identifier can be sent to other processes so that a table can be shared between different processes within a node.
The parameter Options
is a list of atoms which specifies
table type, access rights, key position and if the table is named
or not. If one or more options are left out, the default values
are used. This means that not specifying any options ([]
) is
the same as specifying [set,protected,{keypos,1}]
.
set
The table is a set
table - one key, one object, no
order among objects. This is the default table type.ordered_set
The table is a ordered_set
table - one key, one
object, ordered in Erlang term order, which is the order
implied by the < and > operators. Tables of this type
have a somewhat different behavior in some situations
than tables of the other types.bag
The table is a bag
table which can have many objects,
but only one instance of each object, per key.duplicate_bag
The table is a duplicate_bag
table which can have many
objects, including multiple copies of the same object, per
key.public
Any process may read or write to the table.protected
The owner process can read and write to the table. Other
processes can only read the table. This is the default
setting for the access rights.private
Only the owner process can read or write to the table.named_table
If this option is present, the name Name
is associated
with the table identifier. The name can then be used
instead of the table identifier in subsequent operations.{keypos,Pos}
Specfies which element in the stored tuples should be used as
key. By default, it is the first element, i.e. Pos=1
.
However, this is not always appropriate. In particular,
we do not want the first element to be the key if we want to
store Erlang records in a table.Pos
number of elements.next(Tab, Key1) -> Key2 | '$end_of_table'
Types:
Tab = tid() | atom()
Key1 = Key2 = term()
Returns the next key Key2
, following the key Key1
in the table Tab
. If the table is of the ordered_set
type, the next key in Erlang term order is returned. If the table
is of any other type, the next key according to the table's
internal order is returned. If there is no next key,
'$end_of_table'
is returned.
Use first/1
to find the first key in the table.
Unless a table of type set
, bag
or
duplicate_bag
is protected using safe_fixtable/2
,
see below, a traversal may fail if concurrent updates are made
to the table.
If the table is of type ordered_set
, the function returns
the next key in order, even if the object does no longer exist.
prev(Tab, Key1) -> Key2 | '$end_of_table'
Types:
Tab = tid() | atom()
Key1 = Key2 = term()
Returns the previous key Key2
, preceding the key
Key1
according the Erlang term order in the table
Tab
of the ordered_set
type. If the table is of
any other type, the function is synonymous to next/2
.
If there is no previous key, '$end_of_table'
is returned.
Use last/1
to find the last key in the table.
Types:
Tab = Name = atom()
Renames the named table Tab
to the new name Name
.
Afterwards, the old name can not be used to access the table.
Renaming an unnamed table has no effect.
safe_fixtable(Tab, true|false) -> true | false
Types:
Tab = tid() | atom()
Fixes a table of the set
, bag
or
duplicate_bag
table type for safe traversal.
A process fixes a table by calling safe_fixtable(Tab,true)
.
The table remains fixed until the process releases it by calling
safe_fixtable(Tab,false)
, or until the process terminates.
If several processes fix a table, the table will remain fixed until all processes have released it (or terminated). A reference counter is kept on a per process basis, and N consecutive fixes requires N releases to actually release the table.
When a table is fixed, a sequence of first/1
and
next/2
calls are guaranteed to succeed even if objects
are removed during the traversal. An example:
clean_all_with_value(Tab,X) -> safe_fixtable(Tab,true), clean_all_with_value(Tab,X,ets:first(Tab)), safe_fixtable(Tab,false). clean_all_with_value(Tab,X,'$end_of_table') -> true; clean_all_with_value(Tab,X,Key) -> case ets:lookup(Tab,Key) of [{Key,X}] -> ets:delete(Tab,Key); _ -> true end, clean_all_with_value(Tab,X,ets:next(Tab,Key)).
Note that no deleted objects are actually removed from a fixed table until it has been released. If a process fixes a table but never releases it, the memory used by the deleted objects will never be freed. The performance of operations on the table will also degrade significantly.
Use info/2
to retrieve information about which processes
have fixed which tables. A system with a lot of processes fixing
tables may need a monitor which sends alarms when tables have
been fixed for too long.
Note that for tables of the ordered_set
type,
safe_fixtable/2
is not necessary as calls to first/1
and next/2
will always succeed.
select(Tab, MatchSpec) -> [Object]
Types:
Tab = tid() | atom()
Object = tuple()
MatchSpec = term()
Matches the objects in the table Tab
using a
match_spec as described in ERTS users guide. This is a more
general call than the ets:match/2
and
ets:match_object/2
calls. In its simplest forms the
match_spec's
look like this:
This means that the match_spec is always a list of one or
more tuples (of arity 3). The tuples first element should be
a pattern as destcribed in the documentation of
ets:match/2
. The second element of the tuple should
be a list of 0 or more guard tests (described below). The
third element of the tuple should be a list containing a
description of the value to actually return. In almost all
normal cases the list contains exactly one term which fully
describes the value to return for each object.
The return value is constructed using the "match variables"
bound in the MatchHead or using the special match variables
'$_'
(the whole matching object) and '$$' (all match
variables in a list), so that the following
<c>ets:match/2
expression:
ets:match(Tab,{'$1','$2','$3'})
is exactly equivalent to:
ets:select(Tab,[{{'$1','$2','$3'},[],['$$']}])
- and the following ets:match_object/2
call:
ets:match_object(Tab,{'$1','$2','$1'})
is exactly equivalent to
ets:select(Tab,[{{'$1','$2','$1'},[],['$_']}])
Composite terms can be constructed in the Result
part
either by simply writing a list, so that this code:
ets:select(Tab,[{{'$1','$2','$3'},[],['$$']}])
gives the same output as:
ets:select(Tab,[{{'$1','$2','$3'},[],[['$1','$2','$3']]}])
i.e. all the bound variables in the match head as a list. If
tuples are to be constructed, one has to write a tuple of
arity 1 with the single element in the tuple beeing the tuple
one wants to construct (as an ordinary tuple could be mistaken
for a Guard
). Therefore the following call:
ets:select(Tab,[{{'$1','$2','$1'},[],['$_']}])
gives the same output as:
ets:select(Tab,[{{'$1','$2','$1'},[],[{{'$1','$2','$3'}}]}])
- this syntax is equivalent to the syntax used in the trace
patterns (see the dbg
module in the
runtime_tools
application).
The Guard
's are constructed as tuples where the first
element is the name of the test (again, see the
match_spec
documentation in ERTS users guide) and the
rest of the elements are the parameters of the test. To check
for a specific type (say a list) of the element bound to the
match variable '$1'
, one would write the test as
{is_list, '$1'}
. If the test fails, the object in the
table won't match and the next MatchFunction
(if any)
will be tried. Most guard tests present in erlang can be used,
but only the new versions prefixed is_
are allowed
(like is_float
, is_atom
etc). An exact list of
the allowed guard tests is present in the match_spec
section of ERTS users guide.
The Guard
section can also contain logic and arithmetic
operations, which are written with the same syntax as the
guard tests (prefix notation), so that a guard test written in
erlang looking like this:
is_integer(X), is_integer(Y), X + Y < 4711
is expressed like this (X replaced with '$1' and Y with '$2'):
[{is_integer, '$1'}, {is_integer, '$2'}, {'<', {'+', '$1', '$2'}, 4711}]
A complete list of the operators is present in the match_spec section of ERTS users guide.
select(Tab, MatchSpec, Limit) -> {[Match],Continuation} | '$end_of_table'
Types:
Tab = tid() | atom()
Object = tuple()
MatchSpec = term()
Continuation = term()
Works like ets:select/2
but only returns a limited
(Limit
) number of matching objects. The
Continuation
term can then be used in subsequent calls
to ets:select/1
to get the next chunk of matching
objects. This is a space efficient way to work on objects in a
table which is still faster than traversing the table object
by object using ets:first/1
and ets:next/1
.
'$end_of_table'
is returned if the table is empty.
select(Continuation) -> {[Match],Continuation} | '$end_of_table'
Types:
Match = [term()]
Continuation = term()
Continues a match started with
ets:select/3
. The next
chunk of the size given in the initial ets:select/3
call is returned together with a new Continuation
that can be used in subsequent calls to this function.
'$end_of_table' is returned when there are no more objects in the table.
select_delete(Tab, MatchSpec) -> NumDeleted
Types:
Tab = tid() | atom()
Object = tuple()
MatchSpec = term()
NumDeleted = integer()
Matches the objects in the table Tab
using a
match_spec as described in ERTS users guide.
If the match_spec returns the atom true
for an
object, that object is removed from the table. For any
other result from the match_spec the object is retained.
This is a more
general call than the ets:match_delete/2
call.
The function returns the number of objects actually deleted from the table.
select_count(Tab, MatchSpec) -> NumMatched
Types:
Tab = tid() | atom()
Object = tuple()
MatchSpec = term()
NumMatched = integer()
Matches the objects in the table Tab
using a
match_spec as described in ERTS users guide.
If the match_spec returns the atom true
for an
object, that object considered a match and is counted. For any
other result from the match_spec the object is not
considered a match and is therefore not counted.
The function could be described as a match_delete/2 that does not actually delete any elements, but only counts them.
The function returns the number of objects matched.
slot(Tab, I) -> [Object] | '$end_of_table'
Types:
Tab = tid() | atom()
I = int()
Object = tuple()
This function is mostly for debugging purpouses, Normally
one should use first/next
or last/prev
instead.
Returns all objects in the I
:th slot of the table
Tab
. A table can be traversed by repeatedly calling
the function, starting with the first slot I=0
and
ending when '$end_of_table'
is returned.
The function will fail with reason badarg
if the I
argument is out of range.
Unless a table of type set
, bag
or
duplicate_bag
is protected using safe_fixtable/2
,
see above, a traversal may fail if concurrent updates are made
to the table.
If the table is of type ordered_set
, the function returns
a list containing the I
:th object in Erlang term order.
tab2file(Tab, Filename) -> ok | {error,Reason}
Types:
Tab = tid() | atom()
Filename = string() | atom()
Reason = term()
Dumps the table Tab
to the file Filename
.
The implementation of this function is not efficient.
Types:
Tab = tid() | atom()
Object = tuple()
Returns a list of all objects in the table Tab
.
test_ms(Tuple, MatchSpec) -> {ok, Result} | {error, Errors}
Types:
Tuple = tuple()
MatchSpec = term()
Result = term()
Errors = [{warning|error, string()}]
This function is a utility to test the match_spec
's
used in calls to ets:select/2
. The function both
tests the MatchSpec
for "syntactic" correctness and
runs the match_spec against the object Tuple
. If the
match_spec contains errors, the tuple {error, Errors}
is returned where Errors
is a list of natural
language descriptions of what was wrong with the
match_spec. If the match_spec is syntactically OK, the
function returns {ok,Term}
where Term
is what
would have been the result in a real ets:select/2
call or false
if the match_spec
does not match
the object Tuple
.
This is a useful debugging and test tool, especially when
writing complicated ets:select/2
calls.
Types:
Tab = tid() | atom()
DetsTab = atom()
Fills an already created/opened DETS table with the objects in the
already opened ETS table named Tab
. The DETS table
is emptied before the objects are inserted.
update_counter(Tab, Key, {Pos,Incr,Threshold,SetValue}) -> Result
update_counter(Tab, Key, {Pos,Incr}) -> Result
update_counter(Tab, Key, Incr) -> Result
Types:
Tab = tid() | atom()
Key = term()
Pos = Incr = Threshold = SetValue = Result = int()
This functions provides an efficient way to update a counter, without the hassle of having to look up an object, update the object by incrementing an element and insert the resulting object into the table again.
It will destructively update the object with key Key
in
the table Tab
by adding Incr
to the element at
the Pos
:th position. The new counter value is returned.
If no position is specified, the element directly following
the key (<keypos>+1
) is updated.
If a Threshold
is specified, the counter will be
reset to the value SetValue
if the following
conditions occur:
Incr
is not negative (>= 0
) and the
result would be greater than (>
) Threshold
Incr
is negative (< 0
) and the
result would be less than (<
)
Threshold
The function will fail with reason badarg
if:
set
or ordered_set
,
Pos
, Incr
, Threshold
or
SetValue
is not an integer