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repo_proxy.ex
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repo_proxy.ex
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defmodule Surgex.DataPipe.RepoProxy do
@moduledoc """
Proxies repo calls depending on replication needs.
"""
defmodule Registry do
@moduledoc false
use GenServer
def start_link(opts) do
name = Keyword.fetch!(opts, :name)
GenServer.start_link(__MODULE__, [table_name: name], name: name)
end
def init(opts) do
table_name = Keyword.fetch!(opts, :table_name)
:ets.new(
table_name,
[:set, :named_table, {:keypos, 1}, :public, {:write_concurrency, true}]
)
{:ok, table_name}
end
def handle_cast({:monitor, pid}, state) do
Process.monitor(pid)
{:noreply, state}
end
def handle_info({:DOWN, _ref, :process, pid, _reason}, state = table_name) do
:ets.delete(table_name, pid)
{:noreply, state}
end
def register(name, pool, repo) do
pid = self()
GenServer.cast(name, {:monitor, pid})
true = :ets.insert(name, {pid, pool, repo})
end
def lookup(name, pool) do
case {pool, :ets.lookup(name, self())} do
{_, []} -> nil
{:write, [{_, :read, _}]} -> nil
{_, [{_, _, repo}]} -> repo
end
end
end
alias Mix.Project
alias Surgex.DataPipe.FollowerSync
@read_funcs [
aggregate: 3,
aggregate: 4,
all: 1,
all: 2,
get!: 2,
get!: 3,
get: 2,
get: 3,
get_by!: 2,
get_by!: 3,
get_by: 2,
get_by: 3,
one!: 1,
one!: 2,
one: 1,
one: 2,
preload: 2,
preload: 3
]
@write_funcs [
delete!: 1,
delete!: 2,
delete: 1,
delete: 2,
delete_all: 1,
delete_all: 2,
insert!: 1,
insert!: 2,
insert: 1,
insert: 2,
insert_all: 2,
insert_all: 3,
insert_or_update!: 1,
insert_or_update!: 2,
insert_or_update: 1,
insert_or_update: 2,
transaction: 1,
transaction: 2,
update!: 1,
update!: 2,
update: 1,
update: 2,
update_all: 2,
update_all: 3
]
defmacro __using__(_) do
registry_name = :"#{__CALLER__.module}.Registry"
proxy_ast =
quote do
use Supervisor
require Logger
def start_link do
Supervisor.start_link(__MODULE__, nil, name: __MODULE__)
end
def init(_) do
import Supervisor.Spec
repos = Enum.map(get_repos(), &supervisor(&1, []))
registry = worker(Registry, [[name: unquote(registry_name)]])
opts = [strategy: :one_for_one]
Supervisor.init([registry | repos], opts)
end
@doc """
Calls given repo function on master or replica.
## Options
- `:pool` - one of `:read`/`:write` (by default it's inferred from function name & arity)
"""
def proxy(func, args, opts \\ []) do
arity = length(args)
pool = get_pool(func, arity, opts)
process_repo = get_process_repo(pool)
repo = process_repo || get_repo(pool)
Registry.register(unquote(registry_name), pool, repo)
Logger.debug(fn ->
source = if process_repo, do: "registry", else: "#{pool} pool"
"Proxy #{func}/#{arity} through #{inspect(__MODULE__)} to #{inspect(repo)} (from #{
source
})"
end)
apply(repo, func, args)
end
defp get_pool(func, arity, opts) do
Keyword.get_lazy(opts, :pool, fn ->
cond do
Enum.member?(unquote(@read_funcs), {func, arity}) ->
:read
Enum.member?(unquote(@write_funcs), {func, arity}) ->
:write
true ->
raise("Cannot determine pool for #{func}/#{arity}")
end
end)
end
@doc """
Returns repo that was previously used by current process (if applicable for given pool).
"""
def get_process_repo(pool \\ :read) do
Registry.lookup(unquote(registry_name), pool)
end
@doc """
Returns all proxied repos used for a given pool.
"""
def get_repos(pool \\ :all)
def get_repos(:all), do: get_repos(:write) ++ get_repos(:read)
def get_repos(:read), do: get_config(:replicas, [])
def get_repos(:write), do: [get_config!(:master)]
@doc """
Returns one of proxied repos for a given pool.
"""
def get_repo(pool) do
if test_mode?() do
:write
|> get_repos
|> List.first()
else
preferred_pool = get_repos(pool)
case length(preferred_pool) do
0 ->
Enum.random(get_repos(:all))
_ ->
Enum.random(preferred_pool)
end
end
end
defp test_mode? do
get_config(:test_mode, false)
end
defp get_config(key, default \\ nil) do
Project.config()[:app]
|> Application.get_env(__MODULE__, [])
|> Keyword.get(key, default)
end
defp get_config!(key) do
get_config(key) || raise("#{inspect(key)} not set for #{inspect(__MODULE__)}")
end
def acquire_sync do
with process_repo when not is_nil(process_repo) <- get_process_repo(),
[master_repo] when master_repo != process_repo <- get_repos(:write),
{:ok, lsn} <- PostgresSystemUtils.get_current_wal_lsn(master_repo) do
FollowerSync.call(process_repo, lsn)
else
_ -> :ok
end
end
end
repo_func_asts =
Enum.map(@read_funcs ++ @write_funcs, fn {func_name, func_arity} ->
func_args =
case func_arity do
0 -> []
arity -> Enum.map(1..arity, &Macro.var(:"arg#{&1}", __CALLER__.module))
end
quote do
def unquote(func_name)(unquote_splicing(func_args)) do
proxy(unquote(func_name), [unquote_splicing(func_args)])
end
end
end)
[proxy_ast] ++ repo_func_asts
end
end