About

nsync is a redis master/slave replication client written in Erlang. When the nsync process starts, it opens a tcp socket connected to the master redis server and issues a "SYNC" command. The redis master asynchronously dumps its dataset to disk and transfers it to the nsync slave as an rdb dump. The master then streams subsequent updates to the slave using the redis text protocol.

Build

$ ./rebar compile

Run

$ erl -pa ebin
$ nsync:start_link().

Options

nsync:start_link([Opt]).
Opt = {ip, Ip} |
      {port, Port} |
      {pass, Pass} |
      {callback, Callback} |
      {block, Block} |
      {timeout, Timeout}
Ip = list() % redis master IP
Port = integer() % redis master port
Pass = list() % redis master password
Block = boolean() % block calling pid during sync process
Timeout = integer() % timeout of blocking sync process
Callback = {M, F} | {M, F, A} | Fun
M = atom()
F = atom()
A = list()
Fun = fun()

Examples

PREREQUISITE: Populating redis data

$ ./redis-cli
redis> flushdb
OK
redis> set foo monkey
OK
redis> set foo:one donkey
OK
redis> set bar:one seahorse
OK
redis> set bar:two jellyfish
OK
redis> keys *
1) "foo:one"
2) "foo"
3) "bar:two"
4) "bar:one"

Basic async sync

nsync will perform the sync process in the background

$ erl -pa ebin
1> nsync:start_link().
{ok,<0.33.0>}
2> ets:tab2list(nsync:tid()).
[{<<"foo">>,<<"monkey">>},
 {<<"bar:one">>,<<"seahorse">>},
 {<<"bar:two">>,<<"jellyfish">>},
 {<<"foo:one">>,<<"donkey">>}]

Basic blocking sync

nsync will block the calling pid until the sync process has completed

$ erl -pa ebin
1> nsync:start_link([{block, true}]).
{ok,<0.33.0>}
2> ets:tab2list(nsync:tid()).
[{<<"foo">>,<<"monkey">>},
 {<<"bar:one">>,<<"seahorse">>},
 {<<"bar:two">>,<<"jellyfish">>},
 {<<"foo:one">>,<<"donkey">>}]

Callbacks

nsync supports custom callbacks. The callback module/function is specified in the nsync:start_link options.

The callback module/function should handle any or all of the following tuples:

{load, Key::binary(), Value::binary()} % load a key/value from the rdb dump
{load, eof} % the {load, eof} tuple is sent to the callback when the rdb sync is complete.
{error, closed} % nsync re-establishes the tcp connection and re-issues the SYNC command when the socket is closed. A tuple of the form, {error, closed} is sent to the callback when the socket closes.
{error, {unhandled, Cmd::binary()}}
{cmd, Cmd::binary(), Args::list()} % process an update command/args

The default callback function is nsync:default_callback()

Example1: Custom callback

see example1.erl

$ erl -pa ebin
1> example1:sync().
ok
2> ets:tab2list(nsync:tid(foo)).
[{<<"foo">>,<<"monkey">>},
 {<<"foo:one">>,<<"donkey">>}]
3> ets:tab2list(nsync:tid(bar)).
[{<<"bar:one">>,<<"seahorse">>},
 {<<"bar:two">>,<<"jellyfish">>}]