From 805748eb668d5562fe17f3172cdae07a86166c3f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Thu, 4 Oct 2018 10:30:05 +0200 Subject: Add a persistent term storage Persistent terms are useful for storing Erlang terms that are never or infrequently updated. They have the following advantages: * Constant time access. A persistent term is not copied when it is looked up. The constant factor is lower than for ETS, and no locks are taken when looking up a term. * Persistent terms are not copied in garbage collections. * There is only ever one copy of a persistent term (until it is deleted). That makes them useful for storing configuration data that needs to be easily accessible by all processes. Persistent terms have the following drawbacks: * Updates are expensive. The hash table holding the keys for the persistent terms are updated whenever a persistent term is added, updated or deleted. * Updating or deleting a persistent term triggers a "global GC", which will schedule a heap scan of all processes to search the heap of all processes for the deleted term. If a process still holds a reference to the deleted term, the process will be garbage collected and the term copied to the heap of the process. This global GC can make the system less responsive for some time. Three BIFs (implemented in C in the emulator) is the entire interface to the persistent term functionality: * put(Key, Value) to store a persistent term. * get(Key) to look up a persistent term. * erase(Key) to delete a persistent term. There are also two additional BIFs to obtain information about persistent terms: * info() to return a map with information about persistent terms. * get() to return a list of a {Key,Value} tuples for all persistent terms. (The values are not copied.) --- erts/emulator/beam/atom.names | 3 +++ 1 file changed, 3 insertions(+) (limited to 'erts/emulator/beam/atom.names') diff --git a/erts/emulator/beam/atom.names b/erts/emulator/beam/atom.names index 45b7540aeb..82bb620d62 100644 --- a/erts/emulator/beam/atom.names +++ b/erts/emulator/beam/atom.names @@ -182,6 +182,7 @@ atom control atom copy atom copy_literals atom counters +atom count atom cpu atom cpu_timestamp atom cr @@ -287,6 +288,7 @@ atom gc_minor_end atom gc_minor_start atom Ge='>=' atom generational +atom get_all_trap atom get_seq_token atom get_tcw atom gather_gc_info_result @@ -325,6 +327,7 @@ atom index atom infinity atom info atom info_msg +atom info_trap atom init atom initial_call atom input -- cgit v1.2.3