Asynchronous fork of wg/epgsql originally here: mabrek/epgsql and subsequently forked in order to provide a common fork for community development.
When you need to execute several queries, it involves a number network round-trips between the application and the database. The PostgreSQL frontend/backend protocol supports request pipelining. This means that you don't need to wait for the previous command to finish before sending the next command. This version of the driver makes full use of the protocol feature that allows faster execution.
- 3 API sets:
- epgsql maintains backwards compatibility with the original driver API
- epgsqla delivers complete results as regular erlang messages
- epgsqli delivers results as messages incrementally (row by row)
- internal queue of client requests, so you don't need to wait for the response to send the next request
- single process to hold driver state and receive socket data
- execution of several parsed statements as a batch
- binding timestamps in
erlang:now()format
see CHANGES for full list.
- Unnamed statements are used unless specified otherwise. This may cause problems for people attempting to use the same connection concurrently, which will no longer work.
- SSL performance can degrade if the driver process has a large inbox (thousands of messages).
-type host() :: inet:ip_address() | inet:hostname().
-type connect_option() ::
{database, DBName :: string()} |
{port, PortNum :: inet:port_number()} |
{ssl, IsEnabled :: boolean() | required} |
{ssl_opts, SslOptions :: [ssl:ssl_option()]} | % @see OTP ssl app, ssl_api.hrl
{timeout, TimeoutMs :: timeout()} | % default: 5000 ms
{async, Receiver :: pid()}. % process to receive LISTEN/NOTIFY msgs
-spec connect(host(), string(), string(), [connect_option()])
-> {ok, Connection :: connection()} | {error, Reason :: connect_error()}.
%% @doc connects to Postgres
%% where
%% `Host' - host to connect to
%% `Username' - username to connect as, defaults to `$USER'
%% `Password' - optional password to authenticate with
%% `Opts' - proplist of extra options
%% returns `{ok, Connection}' otherwise `{error, Reason}'
connect(Host, Username, Password, Opts) -> ...example:
{ok, C} = epgsql:connect("localhost", "username", "psss", [
{database, "test_db"},
{timeout, 4000}
]),
...
ok = epgsql:close(C).The {timeout, TimeoutMs} parameter will trigger an {error, timeout} result when the
socket fails to connect within TimeoutMs milliseconds.
Asynchronous connect example (applies to epgsqli too):
{ok, C} = epgsqla:start_link(),
Ref = epgsqla:connect(C, "localhost", "username", "psss", [{database, "test_db"}]),
receive
{C, Ref, connected} ->
{ok, C};
{C, Ref, Error = {error, _}} ->
Error;
{'EXIT', C, _Reason} ->
{error, closed}
end.-type query() :: string() | iodata().
-type squery_row() :: {binary()}.
-record(column, {
name :: binary(),
type :: epgsql_type(),
size :: -1 | pos_integer(),
modifier :: -1 | pos_integer(),
format :: integer()
}).
-type ok_reply(RowType) ::
{ok, Count :: non_neg_integer()} | % select
{ok, ColumnsDescription :: [#column{}], RowsValues :: [RowType]} | % update/insert
{ok, Count :: non_neg_integer(), ColumnsDescription :: [#column{}], RowsValues :: [RowType]}. % update/insert + returning
-type error_reply() :: {error, query_error()}.
-type reply(RowType) :: ok_reply() | error_reply().
-spec squery(connection(), query()) -> reply(squery_row()) | [reply(squery_row())].
%% @doc runs simple `SqlQuery' via given `Connection'
squery(Connection, SqlQuery) -> ...examples:
InsertRes = epgsql:squery(C, "insert into account (name) values ('alice'), ('bob')"),
io:format("~p~n", [InsertRes]),{ok,2}
```erlang
SelectRes = epgsql:squery(C, "select * from account"),
io:format("~p~n", [SelectRes]).
{ok, [{column,<<"id">>,int4,4,-1,0},{column,<<"name">>,text,-1,-1,0}], [{<<"1">>,<<"alice">>},{<<"2">>,<<"bob">>}] }
```erlang
InsertReturningRes = epgsql:squery(C,
"insert into account(name)"
" values ('joe'), (null)"
" returning *"),
io:format("~p~n", [InsertReturningRes]).
{ok,2, [{column,<<"id">>,int4,4,-1,0}, {column,<<"name">>,text,-1,-1,0}], [{<<"3">>,<<"joe">>},{<<"4">>,null}] }
```erlang
{error, Reason} = epgsql:squery(C, "insert into account values (1, 'bad_pkey')"),
io:format("~p~n", [Reason]).
{error, error, <<"23505">>, <<"duplicate key value violates unique constraint "account_pkey"">>, [{detail,<<"Key (id)=(1) already exists.">>}] }
The simple query protocol returns all columns as binary strings
and does not support parameters binding.
Several queries separated by semicolon can be executed by squery.
```erlang
[{ok, _, [{<<"1">>}]}, {ok, _, [{<<"2">>}]}] = epgsql:squery(C, "select 1; select 2").
epgsqla:squery/2 returns result as a single message:
Ref = epgsqla:squery(C, Sql),
receive
{C, Ref, Result} -> Result
end.Result has the same format as return value of epgsql:squery/2.
epgsqli:squery/2 returns results incrementally for each query inside Sql and for each row:
Ref = epgsqli:squery(C, Sql),
receive
{C, Ref, {columns, Columns}} ->
%% columns description
Columns;
{C, Ref, {data, Row}} ->
%% single data row
Row;
{C, Ref, {error, _E} = Error} ->
Error;
{C, Ref, {complete, {_Type, Count}}} ->
%% execution of one insert/update/delete has finished
{ok, Count}; % affected rows count
{C, Ref, {complete, _Type}} ->
%% execution of one select has finished
ok;
{C, Ref, done} ->
%% execution of all queries from Sql has been finished
done;
end.{ok, Columns, Rows} = epgsql:equery(C, "select ...", [Parameters]).
{ok, Count} = epgsql:equery(C, "update ...", [Parameters]).
{ok, Count, Columns, Rows} = epgsql:equery(C, "insert ... returning ...", [Parameters]).
{error, Error} = epgsql:equery(C, "invalid SQL", [Parameters]).Parameters - optional list of values to be bound to $1, $2, $3, etc.
The extended query protocol combines parse, bind, and execute using
the unnamed prepared statement and portal. A select statement returns
{ok, Columns, Rows}, insert/update/delete returns {ok, Count} or
{ok, Count, Columns, Rows} when a returning clause is present. When
an error occurs, all statements result in {error, #error{}}.
SelectRes = epgsql:equery(C, "select id from account where name = $1", ["alice"]),
io:format("~p~n", [SelectRes]).{ok, [{column,<<"id">>,int4,4,-1,1}], [{1}] }
PostgreSQL's binary format is used to return integers as Erlang
integers, floats as floats, bytes/text/varchar columns as binaries,
bools as true/false, etc. For details see `pgsql_binary.erl` and the
Data Representation section below.
Asynchronous API `epgsqla:equery/3` requires you to parse statement beforehand
```erlang
Ref = epgsqla:equery(C, Statement, [Parameters]),
receive
{C, Ref, Res} -> Res
end.
Statement- parsed statement (see parse below)Reshas same format as return value ofepgsql:equery/3.
epgsqli:equery(C, Statement, [Parameters]) sends same set of messages as
squery including final {C, Ref, done}.
{ok, Statement} = epgsql:parse(C, [StatementName], Sql, [ParameterTypes]).StatementName- optional, reusable, name for the prepared statement.ParameterTypes- optional list of PostgreSQL types for each parameter.
For valid type names see pgsql_types.erl.
epgsqla:parse/2 sends {C, Ref, {ok, Statement} | {error, Reason}}.
epgsqli:parse/2 sends:
{C, Ref, {types, Types}}{C, Ref, {columns, Columns}}{C, Ref, no_data}if statement will not return rows{C, Ref, {error, Reason}}
ok = epgsql:bind(C, Statement, [PortalName], ParameterValues).PortalName- optional name for the result portal.
both epgsqla:bind/3 and epgsqli:bind/3 send {C, Ref, ok | {error, Reason}}
{ok | partial, Rows} = epgsql:execute(C, Statement, [PortalName], [MaxRows]).
{ok, Count} = epgsql:execute(C, Statement, [PortalName]).
{ok, Count, Rows} = epgsql:execute(C, Statement, [PortalName]).PortalName- optional portal name used inepgsql:bind/4.MaxRows- maximum number of rows to return (0 for all rows).
epgsql:execute/3 returns {partial, Rows} when more rows are available.
epgsqla:execute/3 sends {C, Ref, Result} where Result has same format as
return value of epgsql:execute/3.
epgsqli:execute/3 sends
{C, Ref, {data, Row}}{C, Ref, {error, Reason}}{C, Ref, suspended}partial result was sent, more rows are available{C, Ref, {complete, {_Type, Count}}}{C, Ref, {complete, _Type}}
ok = epgsql:close(C, Statement).
ok = epgsql:close(C, statement | portal, Name).
ok = epgsql:sync(C).All epgsql functions return {error, Error} when an error occurs.
epgsqla/epgsqli modules' close and sync functions send {C, Ref, ok}.
Batch execution is bind + execute for several prepared statements.
It uses unnamed portals and MaxRows = 0.
Results = epgsql:execute_batch(C, Batch).Batch- list of {Statement, ParameterValues}Results- list of {ok, Count} or {ok, Count, Rows}
example:
{ok, S1} = epgsql:parse(C, "one", "select $1", [int4]),
{ok, S2} = epgsql:parse(C, "two", "select $1 + $2", [int4, int4]),
[{ok, [{1}]}, {ok, [{3}]}] = epgsql:execute_batch(C, [{S1, [1]}, {S2, [1, 2]}]).epgsqla:execute_batch/3 sends {C, Ref, Results}
epgsqli:execute_batch/3 sends
{C, Ref, {data, Row}}{C, Ref, {error, Reason}}{C, Ref, {complete, {_Type, Count}}}{C, Ref, {complete, _Type}}{C, Ref, done}- execution of all queries from Batch has finished
| PG type | Representation |
|---|---|
| null | null |
| bool | true |
| char | $A |
| intX | 1 |
| floatX | 1.0 |
| date | {Year, Month, Day} |
| time | {Hour, Minute, Second.Microsecond} |
| timetz | {time, Timezone} |
| timestamp | {date, time} |
| timestamptz | {date, time} |
| interval | {time, Days, Months} |
| text | <<"a">> |
| varchar | <<"a">> |
| bytea | <<1, 2>> |
| array | [1, 2, 3] |
| record | {int2, time, text, ...} (decode only) |
| point | {10.2, 100.12} |
| int4range | [1,5) |
timestamp and timestamptz parameters can take erlang:now() format: {MegaSeconds, Seconds, MicroSeconds}
int4range is a range type for ints (bigint not supported yet) that obeys inclusive/exclusive semantics,
bracket and parentheses respectively. Additionally, infinities are represented by the atoms minus_infinity
and plus_infinity
Errors originating from the PostgreSQL backend are returned as {error, #error{}},
see epgsql.hrl for the record definition. epgsql functions may also return
{error, What} where What is one of the following:
{unsupported_auth_method, Method}- required auth method is unsupportedtimeout- request timed outclosed- connection was closedsync_required- error occured and epgsql:sync must be called
PostgreSQL may deliver two types of asynchronous message: "notices" in response
to notice and warning messages generated by the server, and "notifications" which
are generated by the LISTEN/NOTIFY mechanism.
Passing the {async, Pid} option to epgsql:connect/3 will result in these async
messages being sent to the specified process, otherwise they will be dropped.
Message formats:
{epgsql, Connection, {notification, Channel, Pid, Payload}}Connection- connection the notification occurred onChannel- channel the notification occurred onPid- database session pid that sent notificationPayload- optional payload, only available from PostgreSQL >= 9.0
{epgsql, Connection, {notice, Error}}Connection- connection the notice occurred onError- an#error{}record, seeepgsql.hrl
epgsql is a community driven effort - we welcome contributions! Here's how to create a patch that's easy to integrate:
- Create a new branch for the proposed fix.
- Make sure it includes a test and documentation, if appropriate.
- Open a pull request against the
develbranch of epgsql. - Passing build in travis
In order to run the epgsql tests, you will need to set up a local Postgres database that runs within its own, self-contained directory, in order to avoid modifying the system installation of Postgres.
NOTE: you will need the postgis and hstore extensions to run these tests! On Ubuntu, you can install them with a command like this:
apt-get install postgresql-9.3-postgis-2.1 postgresql-contrib
-
./setup_test_db.sh# This sets up an installation of Postgres in datadir/ -
./start_test_db.sh# Starts a Postgres instance on its own port (10432). -
make create_testdbs# Creates the test database environment. -
make test# Runs the tests
