Module riak_dt_gcounter

Description
Data Types
Function Index
Function Details

A G-Counter CRDT.

Behaviours: riak_dt.

References

Marc Shapiro, Nuno Preguiça, Carlos Baquero, Marek Zawirski (2011) A comprehensive study of Convergent and Commutative Replicated Data Types. http://hal.upmc.fr/inria-00555588/

Description

A G-Counter CRDT. A G-Counter is a Grow-only counter. Modeled as a list of two-tuples. Each entry in the list is an {actor, count} pair. The value of the counter is the sum of all entries in the list. An actor may only update its own entry. An entry can only be incremented. Borrows liberally from argv0 and Justin Sheehy's vclock module in implementation.

See riak_kv_pncounter for a counter that can be decremented

Data Types

gcounter()

abstract datatype: gcounter()

gcounter_op()

gcounter_op() = increment | {increment, pos_integer()}

Function Index

equal/2	Are two `gcounter()`s structurally equal? This is not `value/1` equality.
from_binary/1	Decode binary G-Counter.
merge/2	Merge two `gcounter()`s to a single `gcounter()`.
new/0	Create a new, empty `gcounter()`
new/2	Create a `gcounter()` with an initial update.
parent_clock/2
stat/2
stats/1
to_binary/1	Encode an effecient binary representation of a `gcounter()`
to_binary/2
to_version/2
update/3	`increment` the entry in `GCnt` for `Actor` by 1 or `{increment, Amt}`.
update/4
value/1	The single total value of a `gcounter()`.
value/2	`value/2` is just `value/1` for a `gcounter()`

Function Details

equal/2

equal(VA::gcounter(), VB::gcounter()) -> boolean()

Are two gcounter()s structurally equal? This is not value/1 equality. Two counters might represent the total 42, and not be equal/2. Equality here is that both counters contain the same actors and those actors have the same count.

from_binary/1

from_binary(B::binary()) -> {ok, gcounter()} | {error, invalid_binary} | {error, unsupported_version, Vers::pos_integer()}

Decode binary G-Counter

merge/2

merge(GCnt1::gcounter(), GCnt2::gcounter()) -> gcounter()

Merge two gcounter()s to a single gcounter(). This is the Least Upper Bound function described in the literature.

new/0

new() -> gcounter()

Create a new, empty gcounter()

new/2

new(Id::riak_dt:actor(), Count::pos_integer()) -> gcounter()

Create a gcounter() with an initial update

parent_clock/2

parent_clock(Clock::riak_dt_vclock:vclock(), GCnt::gcounter()) -> gcounter()

stat/2

stat(X1::atom(), GCnt::gcounter()) -> number() | undefined

stats/1

stats(GCnt::gcounter()) -> [{atom(), number()}]

to_binary/1

to_binary(GCnt::gcounter()) -> binary()

Encode an effecient binary representation of a gcounter()

to_binary/2

to_binary(Vers::pos_integer(), C::gcounter()) -> {ok, binary()} | {error, unsupported_version, Vers::pos_integer()}

to_version/2

to_version(Version::pos_integer(), C::gcounter()) -> gcounter()

update/3

update(X1::gcounter_op(), Actor::riak_dt:actor(), GCnt::gcounter()) -> {ok, gcounter()}

increment the entry in GCnt for Actor by 1 or {increment, Amt}. returns an updated gcounter() or error if Amt is not a pos_integer()

update/4

update(Op::gcounter_op(), Actor::riak_dt:actor(), GCnt::gcounter(), Ctx::riak_dt:context()) -> {ok, gcounter()}

value/1

value(GCnt::gcounter()) -> non_neg_integer()

The single total value of a gcounter().

value/2

value(X1::any(), GCnt::gcounter()) -> non_neg_integer()

value/2 is just value/1 for a gcounter()

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