anchor

High-Performance Erlang Memcached Client

Requirements

• Memcached
• Erlang/OTP 25+

Features

• Backpressure via backlog (OOM protection)
• Binary protocol
• Fast pool implementation (random | round_robin)
• Performance optimized
• Request pipelining

API

Function reference on hexdocs

Environment variables

Examples

1> anchor_app:start().
{ok, [shackle, anchor]}

2> anchor:get(<<"foo">>).
{error, key_not_found}

3> anchor:set(<<"foo">>, <<"bar">>, 3600).
ok

4> anchor:get(<<"foo">>).
{ok, <<"bar">>}

5> anchor:delete(<<"foo">>).
ok

6> {ok, Ref} = anchor:async_get(<<"foo">>).
{ok, {anchor_6, #Ref<0.0.1.1363>}}

7> anchor:receive_response(Ref, 1000).
{error, key_not_found}

Errors

All anchor:* calls return ok | {ok, term()} | {error, error_reason()} where error_reason/0 (exported, added in 0.3.8) enumerates:

• Memcached protocol statuses — auth_continue, auth_error, busy, incr_non_numeric, internal_error, invalid_args, item_not_stored, key_exists, key_not_found, not_supported, out_of_memory, temp_failure, unknown_command, value_too_large, vbucket_error.
• Shackle errors that propagate through anchor — no_server, pool_not_started, shackle_not_started, timeout.

The closed sum lets dialyzer catch typos in case patterns at call sites.

Telemetry

anchor emits one telemetry event at the request boundary. Attach handlers via telemetry:attach/4:

Event	Measurements	Metadata
[anchor, request, sent]	count => 1	operation, async

Fires from the two internal dispatch helpers (call/2 and cast/3), so all 77 exported public functions are covered without per-arity instrumentation. The operation metadata is the memcached op (get, set, add, replace, delete, flush, noop, quit, version, increment, decrement).

Per-request shackle lifecycle (queue / send / receive) remains observable via shackle's own telemetry — anchor's event surfaces the memcached-level intent without duplicating that work.

Tests

make test

License

The MIT License (MIT)

Copyright (c) 2014-2026 Louis-Philippe Gauthier

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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SOFTWARE.