A good start when programming efficiently is to know how much memory different data types and operations require. It is implementation-dependent how much memory the Erlang data types and other items consume, but the following table shows some figures for the
erts-8.0 system in OTP 19.0.
The unit of measurement is memory words. There exists both a 32-bit and a 64-bit implementation. A word is therefore 4 bytes or 8 bytes, respectively.
|Data Type||Memory Size|
|Small integer||1 word. |
On 32-bit architectures: -134217729 < i < 134217728 (28 bits).
On 64-bit architectures: -576460752303423489 < i < 576460752303423488 (60 bits).
|Large integer||3..N words.|
|Atom||1 word. |
An atom refers into an atom table, which also consumes memory. The atom text is stored once for each unique atom in this table. The atom table is not garbage-collected.
|Float||On 32-bit architectures: 4 words. |
On 64-bit architectures: 3 words.
|Binary||3..6 words + data (can be shared).|
|List||1 word + 1 word per element + the size of each element.|
|String (is the same as a list of integers)||1 word + 2 words per character.|
|Tuple||2 words + the size of each element.|
|Small Map||5 words + the size of all keys and values.|
|Large Map (> 32 keys)|| |
|Pid||1 word for a process identifier from the current local node + 5 words for a process identifier from another node. |
A process identifier refers into a process table and a node table, which also consumes memory.
|Port||1 word for a port identifier from the current local node + 5 words for a port identifier from another node. |
A port identifier refers into a port table and a node table, which also consumes memory.
|Reference||On 32-bit architectures: 5 words for a reference from the current local node + 7 words for a reference from another node. |
On 64-bit architectures: 4 words for a reference from the current local node + 6 words for a reference from another node.
A reference refers into a node table, which also consumes memory.
|Fun||9..13 words + the size of environment. |
A fun refers into a fun table, which also consumes memory.
|Ets table||Initially 768 words + the size of each element (6 words + the size of Erlang data). The table grows when necessary.|
|Erlang process||338 words when spawned, including a heap of 233 words.|
The Erlang language specification puts no limits on the number of processes, length of atoms, and so on. However, for performance and memory saving reasons, there will always be limits in a practical implementation of the Erlang language and execution environment.
|Processes||The maximum number of simultaneously alive Erlang processes is by default 32,768. This limit can be configured at startup. For more information, see the |
|Known nodes||A remote node Y must be known to node X if there exists any pids, ports, references, or funs (Erlang data types) from Y on X, or if X and Y are connected. The maximum number of remote nodes simultaneously/ever known to a node is limited by the |
|Connected nodes||The maximum number of simultaneously connected nodes is limited by either the maximum number of simultaneously known remote nodes, |
|Characters in an atom||255.|
|Atoms||By default, the maximum number of atoms is 1,048,576. This limit can be raised or lowered using the |
|Ets tables||Default is 1400. It can be changed with the environment variable |
|Elements in a tuple||The maximum number of elements in a tuple is 67,108,863 (26-bit unsigned integer). Clearly, other factors such as the available memory can make it difficult to create a tuple of that size.|
|Size of binary||In the 32-bit implementation of Erlang, 536,870,911 bytes is the largest binary that can be constructed or matched using the bit syntax. In the 64-bit implementation, the maximum size is 2,305,843,009,213,693,951 bytes. If the limit is exceeded, bit syntax construction fails with a |
In earlier Erlang/OTP releases, operations on too large binaries in general either fail or give incorrect results. In future releases, other operations that create binaries (such as
|Total amount of data allocated by an Erlang node||The Erlang runtime system can use the complete 32-bit (or 64-bit) address space, but the operating system often limits a single process to use less than that.|
|Length of a node name||An Erlang node name has the form host@shortname or host@longname. The node name is used as an atom within the system, so the maximum size of 255 holds also for the node name.|
|Open ports||The maximum number of simultaneously open Erlang ports is often by default 16,384. This limit can be configured at startup. For more information, see the |
|Open files and sockets||The maximum number of simultaneously open files and sockets depends on |
|Number of arguments to a function or fun||255|
|Unique References on a Runtime System Instance||Each scheduler thread has its own set of references, and all other threads have a shared set of references. Each set of references consist of |
|Unique Integers on a Runtime System Instance||There are two types of unique integers both created using the |
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