使用PostgreSQL的宝石异步 [英] using the postgresql gem async

问题描述

我使用巨人（这是由EventMachine的供电）和Postgres的宝石皮克，目前我使用的是PG宝石阻塞方式： conn.exec（SELECT * FROM产品'）（例如），我想知道是否有连接到一个Postgres数据库更好的办法？

I'm using Goliath (which is powered by eventmachine) and the postgres gem pg, currently I'm using the pg gem in a blocking way: conn.exec('SELECT * FROM products') (for example) and I'm wondering whether there is a better way to connect to a postgres database?

推荐答案

的皮克库提供了PostgreSQL的异步API的全面支持。我已经添加一个例子如何用它来样本/ 目录：

The pg library provides full support for PostgreSQL's asynchronous API. I've added an example of how to use it to the samples/ directory:

#!/usr/bin/env ruby

require 'pg'

# This is a example of how to use the asynchronous API to query the
# server without blocking other threads. It's intentionally low-level;
# if you hooked up the PGconn#socket to some kind of reactor, you
# could make this much nicer.

TIMEOUT = 5.0 # seconds to wait for an async operation to complete
CONN_OPTS = {
    :host     => 'localhost',
    :dbname   => 'test',
    :user     => 'jrandom',
    :password => 'banks!stealUR$',
}

# Print 'x' continuously to demonstrate that other threads aren't
# blocked while waiting for the connection, for the query to be sent,
# for results, etc. You might want to sleep inside the loop or 
# comment this out entirely for cleaner output.
progress_thread = Thread.new { loop { print 'x' } }

# Output progress messages
def output_progress( msg )
    puts "\n>>> #{msg}\n"
end

# Start the connection
output_progress "Starting connection..."
conn = PGconn.connect_start( CONN_OPTS ) or 
    abort "Unable to create a new connection!"
abort "Connection failed: %s" % [ conn.error_message ] if
    conn.status == PGconn::CONNECTION_BAD

# Now grab a reference to the underlying socket so we know when the
# connection is established
socket = IO.for_fd( conn.socket )

# Track the progress of the connection, waiting for the socket to 
# become readable/writable before polling it
poll_status = PGconn::PGRES_POLLING_WRITING
until poll_status == PGconn::PGRES_POLLING_OK ||
      poll_status == PGconn::PGRES_POLLING_FAILED

    # If the socket needs to read, wait 'til it becomes readable to
    # poll again
    case poll_status
    when PGconn::PGRES_POLLING_READING
        output_progress "  waiting for socket to become readable"
        select( [socket], nil, nil, TIMEOUT ) or
            raise "Asynchronous connection timed out!"

    # ...and the same for when the socket needs to write
    when PGconn::PGRES_POLLING_WRITING
        output_progress "  waiting for socket to become writable"
        select( nil, [socket], nil, TIMEOUT ) or
            raise "Asynchronous connection timed out!"
    end

    # Output a status message about the progress
    case conn.status
    when PGconn::CONNECTION_STARTED
        output_progress "  waiting for connection to be made."
    when PGconn::CONNECTION_MADE
        output_progress "  connection OK; waiting to send."
    when PGconn::CONNECTION_AWAITING_RESPONSE
        output_progress "  waiting for a response from the server."
    when PGconn::CONNECTION_AUTH_OK
        output_progress "  received authentication; waiting for " +
                        "backend start-up to finish."
    when PGconn::CONNECTION_SSL_STARTUP
        output_progress "  negotiating SSL encryption."
    when PGconn::CONNECTION_SETENV
        output_progress "  negotiating environment-driven " +
                        "parameter settings."
    end

    # Check to see if it's finished or failed yet
    poll_status = conn.connect_poll
end

abort "Connect failed: %s" % [ conn.error_message ] unless 
    conn.status == PGconn::CONNECTION_OK

output_progress "Sending query"
conn.send_query( "SELECT * FROM pg_stat_activity" )

# Fetch results until there aren't any more
loop do
    output_progress "  waiting for a response"

    # Buffer any incoming data on the socket until a full result 
    # is ready. 
    conn.consume_input
    while conn.is_busy
        select( [socket], nil, nil, TIMEOUT ) or
            raise "Timeout waiting for query response."
        conn.consume_input
    end

    # Fetch the next result. If there isn't one, the query is 
    # finished
    result = conn.get_result or break

    puts "\n\nQuery result:\n%p\n" % [ result.values ]
end

output_progress "Done."
conn.finish

if defined?( progress_thread )
    progress_thread.kill
    progress_thread.join
end

我建议你读了<一个文档href=\"http://www.postgresql.org/docs/9.0/interactive/libpq-connect.html#LIBPQ-PQCONNECTSTARTPARAMS\">PQconnectStart功能和PostgreSQL的手册异步命令处理部分，然后比较，与上述试。

I'd recommend that you read the documentation on the PQconnectStart function and the Asynchronous Command Processing section of the PostgreSQL manual, and then compare that with the sample above.

我以前没有使用EventMachine的，但是如果它让你注册的时候就变成可读/写一个套接字和回调，我觉得这是很容易集成数据库调用到它。

I haven't used EventMachine before, but if it lets you register a socket and callbacks for when it becomes readable/writable, I'd think it'd be fairly easy to integrate database calls into it.

我一直使用中的伊利亚Grigorik的使用纤维清理事件触发code 使异步API更容易使用的文章，但是这是一个办法了。我有门票开放追踪它如果你有兴趣/动机做自己。

I've been meaning to use the ideas in Ilya Grigorik's article on using Fibers to clean up evented code to make the async API easier to use, but that's a ways off. I do have a ticket open to track it if you're interested/motivated to do it yourself.

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