memcached: Lua memcached client driver for nginx-module-lua based on the cosocket API

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install lua-resty-memcached

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

dnf -y install https://extras.getpagespeed.com/release-latest.rpm
dnf -y install lua5.1-resty-memcached

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-memcached v0.17 released on Jan 19 2023.

lua-resty-memcached - Lua memcached client driver for the ngx_lua based on the cosocket API

Status

This library is considered production ready.

Description

This Lua library is a memcached client driver for the ngx_lua nginx module:

http://wiki.nginx.org/HttpLuaModule

This Lua library takes advantage of ngx_lua's cosocket API, which ensures 100% nonblocking behavior.

Note that at least ngx_lua 0.5.0rc29 or OpenResty 1.0.15.7 is required.

Synopsis

    server {
        location /test {
            content_by_lua '
                local memcached = require "resty.memcached"
                local memc, err = memcached:new()
                if not memc then
                    ngx.say("failed to instantiate memc: ", err)
                    return
                end

                memc:set_timeout(1000) -- 1 sec

                -- or connect to a unix domain socket file listened
                -- by a memcached server:
                --     local ok, err = memc:connect("unix:/path/to/memc.sock")

                local ok, err = memc:connect("127.0.0.1", 11211)
                if not ok then
                    ngx.say("failed to connect: ", err)
                    return
                end

                local ok, err = memc:flush_all()
                if not ok then
                    ngx.say("failed to flush all: ", err)
                    return
                end

                local ok, err = memc:set("dog", 32)
                if not ok then
                    ngx.say("failed to set dog: ", err)
                    return
                end

                local res, flags, err = memc:get("dog")
                if err then
                    ngx.say("failed to get dog: ", err)
                    return
                end

                if not res then
                    ngx.say("dog not found")
                    return
                end

                ngx.say("dog: ", res)

                -- put it into the connection pool of size 100,
                -- with 10 seconds max idle timeout
                local ok, err = memc:set_keepalive(10000, 100)
                if not ok then
                    ngx.say("cannot set keepalive: ", err)
                    return
                end

                -- or just close the connection right away:
                -- local ok, err = memc:close()
                -- if not ok then
                --     ngx.say("failed to close: ", err)
                --     return
                -- end
            ';
        }
    }

Methods

The key argument provided in the following methods will be automatically escaped according to the URI escaping rules before sending to the memcached server.

new

syntax: memc, err = memcached:new(opts?)

Creates a memcached object. In case of failures, returns nil and a string describing the error.

It accepts an optional opts table argument. The following options are supported:

key_transform

an array table containing two functions for escaping and unescaping the memcached keys, respectively. By default, the memcached keys will be escaped and unescaped as URI components, that is

    memached:new{
        key_transform = { ngx.escape_uri, ngx.unescape_uri }
    }

connect

syntax: ok, err = memc:connect(host, port)

syntax: ok, err = memc:connect("unix:/path/to/unix.sock")

Attempts to connect to the remote host and port that the memcached server is listening to or a local unix domain socket file listened by the memcached server.

Before actually resolving the host name and connecting to the remote backend, this method will always look up the connection pool for matched idle connections created by previous calls of this method.

sslhandshake

syntax: session, err = memc:sslhandshake(reused_session?, server_name?, ssl_verify?, send_status_req?)

Does SSL/TLS handshake on the currently established connection. See the tcpsock.sslhandshake API from OpenResty for more details.

set

syntax: ok, err = memc:set(key, value, exptime, flags)

Inserts an entry into memcached unconditionally. If the key already exists, overrides it.

The value argument could also be a Lua table holding multiple Lua strings that are supposed to be concatenated as a whole (without any delimiters). For example,

    memc:set("dog", {"a ", {"kind of"}, " animal"})

is functionally equivalent to

    memc:set("dog", "a kind of animal")

The exptime parameter is optional and defaults to 0 (meaning never expires). The expiration time is in seconds.

The flags parameter is optional and defaults to 0.

set_timeout

syntax: ok, err = memc:set_timeout(timeout)

Sets the timeout (in ms) protection for subsequent operations, including the connect method.

Returns 1 when successful and nil plus a string describing the error otherwise.

set_timeouts

syntax: ok, err = memc:set_timeouts(connect_timeout, send_timeout, read_timeout)

Sets the timeouts (in ms) for connect, send and read operations respectively.

Returns 1 when successful and nil plus a string describing the error otherwise.

set_keepalive

syntax: ok, err = memc:set_keepalive(max_idle_timeout, pool_size)

Puts the current memcached connection immediately into the ngx_lua cosocket connection pool.

You can specify the max idle timeout (in ms) when the connection is in the pool and the maximal size of the pool every nginx worker process.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

Only call this method in the place you would have called the close method instead. Calling this method will immediately turn the current memcached object into the closed state. Any subsequent operations other than connect() on the current object will return the closed error.

get_reused_times

syntax: times, err = memc:get_reused_times()

This method returns the (successfully) reused times for the current connection. In case of error, it returns nil and a string describing the error.

If the current connection does not come from the built-in connection pool, then this method always returns 0, that is, the connection has never been reused (yet). If the connection comes from the connection pool, then the return value is always non-zero. So this method can also be used to determine if the current connection comes from the pool.

close

syntax: ok, err = memc:close()

Closes the current memcached connection and returns the status.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

add

syntax: ok, err = memc:add(key, value, exptime, flags)

Inserts an entry into memcached if and only if the key does not exist.

The value argument could also be a Lua table holding multiple Lua strings that are supposed to be concatenated as a whole (without any delimiters). For example,

    memc:add("dog", {"a ", {"kind of"}, " animal"})

is functionally equivalent to

    memc:add("dog", "a kind of animal")

The exptime parameter is optional and defaults to 0 (meaning never expires). The expiration time is in seconds.

The flags parameter is optional, defaults to 0.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

replace

syntax: ok, err = memc:replace(key, value, exptime, flags)

Inserts an entry into memcached if and only if the key does exist.

The value argument could also be a Lua table holding multiple Lua strings that are supposed to be concatenated as a whole (without any delimiters). For example,

    memc:replace("dog", {"a ", {"kind of"}, " animal"})

is functionally equivalent to

    memc:replace("dog", "a kind of animal")

The exptime parameter is optional and defaults to 0 (meaning never expires). The expiration time is in seconds.

The flags parameter is optional, defaults to 0.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

append

syntax: ok, err = memc:append(key, value, exptime, flags)

Appends the value to an entry with the same key that already exists in memcached.

The value argument could also be a Lua table holding multiple Lua strings that are supposed to be concatenated as a whole (without any delimiters). For example,

    memc:append("dog", {"a ", {"kind of"}, " animal"})

is functionally equivalent to

    memc:append("dog", "a kind of animal")

The exptime parameter is optional and defaults to 0 (meaning never expires). The expiration time is in seconds.

The flags parameter is optional, defaults to 0.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

prepend

syntax: ok, err = memc:prepend(key, value, exptime, flags)

Prepends the value to an entry with the same key that already exists in memcached.

The value argument could also be a Lua table holding multiple Lua strings that are supposed to be concatenated as a whole (without any delimiters). For example,

    memc:prepend("dog", {"a ", {"kind of"}, " animal"})

is functionally equivalent to

    memc:prepend("dog", "a kind of animal")

The exptime parameter is optional and defaults to 0 (meaning never expires). The expiration time is in seconds.

The flags parameter is optional and defaults to 0.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

get

syntax: value, flags, err = memc:get(key) syntax: results, err = memc:get(keys)

Get a single entry or multiple entries in the memcached server via a single key or a table of keys.

Let us first discuss the case When the key is a single string.

The key's value and associated flags value will be returned if the entry is found and no error happens.

In case of errors, nil values will be turned for value and flags and a 3rd (string) value will also be returned for describing the error.

If the entry is not found, then three nil values will be returned.

Then let us discuss the case when the a Lua table of multiple keys are provided.

In this case, a Lua table holding the key-result pairs will be always returned in case of success. Each value corresponding each key in the table is also a table holding two values, the key's value and the key's flags. If a key does not exist, then there is no responding entries in the results table.

In case of errors, nil will be returned, and the second return value will be a string describing the error.

gets

syntax: value, flags, cas_unique, err = memc:gets(key)

syntax: results, err = memc:gets(keys)

Just like the get method, but will also return the CAS unique value associated with the entry in addition to the key's value and flags.

This method is usually used together with the cas method.

cas

syntax: ok, err = memc:cas(key, value, cas_unique, exptime?, flags?)

Just like the set method but does a check and set operation, which means "store this data but only if no one else has updated since I last fetched it."

The cas_unique argument can be obtained from the gets method.

touch

syntax: ok, err = memc:touch(key, exptime)

Update the expiration time of an existing key.

Returns 1 for success or nil with a string describing the error otherwise.

This method was first introduced in the v0.11 release.

flush_all

syntax: ok, err = memc:flush_all(time?)

Flushes (or invalidates) all the existing entries in the memcached server immediately (by default) or after the expiration specified by the time argument (in seconds).

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

delete

syntax: ok, err = memc:delete(key)

Deletes the key from memcached immediately.

The key to be deleted must already exist in memcached.

In case of success, returns 1. In case of errors, returns nil with a string describing the error.

incr

syntax: new_value, err = memc:incr(key, delta)

Increments the value of the specified key by the integer value specified in the delta argument.

Returns the new value after incrementation in success, and nil with a string describing the error in case of failures.

decr

syntax: new_value, err = memc:decr(key, value)

Decrements the value of the specified key by the integer value specified in the delta argument.

Returns the new value after decrementation in success, and nil with a string describing the error in case of failures.

stats

syntax: lines, err = memc:stats(args?)

Returns memcached server statistics information with an optional args argument.

In case of success, this method returns a lua table holding all of the lines of the output; in case of failures, it returns nil with a string describing the error.

If the args argument is omitted, general server statistics is returned. Possible args argument values are items, sizes, slabs, among others.

quit

syntax: ok, err = memc:quit()

Tells the server to close the current memcached connection.

Returns 1 in case of success and nil other wise. In case of failures, another string value will also be returned to describe the error.

Generally you can just directly call the close method to achieve the same effect.

verbosity

syntax: ok, err = memc:verbosity(level)

Sets the verbosity level used by the memcached server. The level argument should be given integers only.

Returns 1 in case of success and nil other wise. In case of failures, another string value will also be returned to describe the error.

init_pipeline

syntax: err = memc:init_pipeline(n?)

Enable the Memcache pipelining mode. All subsequent calls to Memcache command methods will automatically get buffer and will send to the server in one run when the commit_pipeline method is called or get cancelled by calling the cancel_pipeline method.

The optional params n is buffer tables size. default value 4

commit_pipeline

syntax: results, err = memc:commit_pipeline()

Quits the pipelining mode by committing all the cached Memcache queries to the remote server in a single run. All the replies for these queries will be collected automatically and are returned as if a big multi-bulk reply at the highest level.

This method success return a lua table. failed return a lua string describing the error upon failures.

cancel_pipeline

syntax: memc:cancel_pipeline()

Quits the pipelining mode by discarding all existing buffer Memcache commands since the last call to the init_pipeline method.

the method no return. always succeeds.

Automatic Error Logging

By default the underlying ngx_lua module does error logging when socket errors happen. If you are already doing proper error handling in your own Lua code, then you are recommended to disable this automatic error logging by turning off ngx_lua's lua_socket_log_errors directive, that is,

    lua_socket_log_errors off;

Limitations

This library cannot be used in code contexts like set_by_lua*, log_by_lua*, and header_filter_by_lua* where the ngx_lua cosocket API is not available.
The resty.memcached object instance cannot be stored in a Lua variable at the Lua module level, because it will then be shared by all the concurrent requests handled by the same nginx worker process (see http://wiki.nginx.org/HttpLuaModule#Data_Sharing_within_an_Nginx_Worker ) and result in bad race conditions when concurrent requests are trying to use the same resty.memcached instance. You should always initiate resty.memcached objects in function local variables or in the ngx.ctx table. These places all have their own data copies for each request.

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-memcached.

memcached: Lua memcached client driver for nginx-module-lua based on the cosocket API

Installation

CentOS/RHEL 7 or Amazon Linux 2

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

Status

Description

Synopsis

Methods

new

connect

sslhandshake

set

set_timeout

set_timeouts

set_keepalive

get_reused_times

close

add

replace

append

prepend

get

gets

cas

touch

flush_all

delete

incr

decr

stats

quit

verbosity

init_pipeline

commit_pipeline

cancel_pipeline

Automatic Error Logging

Limitations

See Also

GitHub