Async IO HTTP server frontend for PostgreSQL

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Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin
Dear community,

I need a %subj% -- high performance HTTP server solution
based on asynchronous IO with ability to run PostgreSQL's
functions from HTML templates asynchronously and passing
the results to the HTTP client.
For example, consider a simple template:
<html>
  <div id="rows">
    ${get_rows(id := :id)}
  </div>
</html>
The function get_rows() will be called asynchronously
during the dispatching HTTP request and the result of
it will streams immediately to the HTTP client via async IO.

Currently, I've found only a module for NGINX
but it does not what I need.

Ideally, it should be a simple C (libevent based) or C++
(boost::asio based) library.

Please, if anyone has a ready solution of the idea described
above, let me know, because I don't want waste my time to write
it from scratch.

--
// Dmitriy.

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Re: Async IO HTTP server frontend for PostgreSQL

Merlin Moncure-2
On Mon, Sep 8, 2014 at 12:59 PM, Dmitriy Igrishin <[hidden email]> wrote:

> Dear community,
>
> I need a %subj% -- high performance HTTP server solution
> based on asynchronous IO with ability to run PostgreSQL's
> functions from HTML templates asynchronously and passing
> the results to the HTTP client.
> For example, consider a simple template:
> <html>
>   <div id="rows">
>     ${get_rows(id := :id)}
>   </div>
> </html>
> The function get_rows() will be called asynchronously
> during the dispatching HTTP request and the result of
> it will streams immediately to the HTTP client via async IO.
>
> Currently, I've found only a module for NGINX
> https://github.com/FRiCKLE/ngx_postgres
> but it does not what I need.
>
> Ideally, it should be a simple C (libevent based) or C++
> (boost::asio based) library.
>
> Please, if anyone has a ready solution of the idea described
> above, let me know, because I don't want waste my time to write
> it from scratch.

It's not in C, but you should take a very good look at node.js.

merlin


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Re: Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin


2014-09-09 1:28 GMT+04:00 Merlin Moncure <[hidden email]>:
On Mon, Sep 8, 2014 at 12:59 PM, Dmitriy Igrishin <[hidden email]> wrote:
> Dear community,
>
> I need a %subj% -- high performance HTTP server solution
> based on asynchronous IO with ability to run PostgreSQL's
> functions from HTML templates asynchronously and passing
> the results to the HTTP client.
> For example, consider a simple template:
> <html>
>   <div id="rows">
>     ${get_rows(id := :id)}
>   </div>
> </html>
> The function get_rows() will be called asynchronously
> during the dispatching HTTP request and the result of
> it will streams immediately to the HTTP client via async IO.
>
> Currently, I've found only a module for NGINX
> https://github.com/FRiCKLE/ngx_postgres
> but it does not what I need.
>
> Ideally, it should be a simple C (libevent based) or C++
> (boost::asio based) library.
>
> Please, if anyone has a ready solution of the idea described
> above, let me know, because I don't want waste my time to write
> it from scratch.

It's not in C, but you should take a very good look at node.js.

merlin
Yeah, it looks interesting and AFAIK there are already bindings
for node.js to asynchronous libpq's API --
Thanks for the point, Merlin.

--
// Dmitriy.

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Re: Async IO HTTP server frontend for PostgreSQL

David Boreham-2
Hi Dmitriy, are you able to say a little about what's driving your quest
for async http-to-pg ?
I'm curious as to the motivations, and whether they match up with some
of my own reasons for wanting to use low-thread-count solutions.

Thanks.




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Re: Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin
Hello, David

2014-09-10 4:31 GMT+04:00 David Boreham <[hidden email]>:
Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.
For many web projects I consider Postgres as a development platform. Thus,
I prefer to keep the business logic (data integrity trigger functions and
API functions) in the database. Because of nature of the Web, many concurrent
clients can request a site and I want to serve maximum possible of them with
minimal overhead. Also I want to avoid a complex solutions. So, I believe that
with asynchronous solution it's possible to *stream* the data from the database
to the maximum number of clients (which possible can request my site over a
slow connection).



--
// Dmitriy.

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Re: Async IO HTTP server frontend for PostgreSQL

John DeSoi
In reply to this post by David Boreham-2

On Sep 9, 2014, at 7:31 PM, David Boreham <[hidden email]> wrote:

> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.

For some discussion and preliminary design, see also

https://wiki.postgresql.org/wiki/HTTP_API

John DeSoi, Ph.D.



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Re: Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin
Hello, John

2014-09-10 17:25 GMT+04:00 John DeSoi <[hidden email]>:

On Sep 9, 2014, at 7:31 PM, David Boreham <[hidden email]> wrote:

> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.

For some discussion and preliminary design, see also

https://wiki.postgresql.org/wiki/HTTP_API

John DeSoi, Ph.D.
While this is not related to the %subj%, I've glanced and the link above.
And I found this complex. (As many many many "nice featured" things
on the market today.) Could you tell me please, for example, why the
URLs like
/databases/:database_name/schemas/:schema_name/tables/:table_name
OR
/databases/:database_name/schemas/:schema_name/table/:table_name/indexes/:index_name
Whats wrong with SQL way to get such info from sys. catalogs or
the information schema?
I guess, I know the answer -- "its just pretty nice and clear". But
I think it's just a waste of time (of users which should learn all of
these fancies, and developers which should implement them).


--
// Dmitriy.

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Re: Async IO HTTP server frontend for PostgreSQL

Steve Atkins
In reply to this post by Dmitry Igrishin

On Sep 10, 2014, at 12:16 AM, Dmitriy Igrishin <[hidden email]> wrote:

> Hello, David
>
> 2014-09-10 4:31 GMT+04:00 David Boreham <[hidden email]>:
> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.
> For many web projects I consider Postgres as a development platform. Thus,
> I prefer to keep the business logic (data integrity trigger functions and
> API functions) in the database. Because of nature of the Web, many concurrent
> clients can request a site and I want to serve maximum possible of them with
> minimal overhead. Also I want to avoid a complex solutions. So, I believe that
> with asynchronous solution it's possible to *stream* the data from the database
> to the maximum number of clients (which possible can request my site over a
> slow connection).

That's going to require you to have one database connection open for each
client. If the client is over a slow connection it'll keep the database connection
open far longer than is needed, (compared to the usual "pull data from the
database as fast as the disks will go, then spoonfeed it out to the slow client"
approach). Requiring a live database backend for every open client connection
doesn't seem like a good idea if you're supporting many slow concurrent clients.

Cheers,
  Steve



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Re: Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin
Hello, Steve

2014-09-10 21:08 GMT+04:00 Steve Atkins <[hidden email]>:

On Sep 10, 2014, at 12:16 AM, Dmitriy Igrishin <[hidden email]> wrote:

> Hello, David
>
> 2014-09-10 4:31 GMT+04:00 David Boreham <[hidden email]>:
> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.
> For many web projects I consider Postgres as a development platform. Thus,
> I prefer to keep the business logic (data integrity trigger functions and
> API functions) in the database. Because of nature of the Web, many concurrent
> clients can request a site and I want to serve maximum possible of them with
> minimal overhead. Also I want to avoid a complex solutions. So, I believe that
> with asynchronous solution it's possible to *stream* the data from the database
> to the maximum number of clients (which possible can request my site over a
> slow connection).

That's going to require you to have one database connection open for each
client. If the client is over a slow connection it'll keep the database connection
open far longer than is needed, (compared to the usual "pull data from the
database as fast as the disks will go, then spoonfeed it out to the slow client"
approach). Requiring a live database backend for every open client connection
doesn't seem like a good idea if you're supporting many slow concurrent clients.
Good point. Thus, some of caching on the HTTP server side should be implemented
then.


--
// Dmitriy.

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Re: Async IO HTTP server frontend for PostgreSQL

Allan Kamau-3

Dear Dmitriy,

To add on to David's suggestions, Data caching is a difficult task to undertake. Consider an example where your data may not all fit into memory, when you cache these data outside PostgreSQL you would need to look into memory management as well as issues around concurrent population of this cache as well as means to keep the data in the cache fresh in tune with any changes to the data. These are no trivial tasks and the database community has spent years constructing and improving algorithms to do this on behalf of the front end database application developer. Also each time a TCP connection is created, additional compute resources are consumed by the OS as well as the database management server software.

A simpler way would be to use connection pooling where a thread of your running application "borrows" a connection from a pool of open connections, executes the SQL command then returns the connection immediately on completion of the SQL command. This will require few concurrent connections (depending of configuration) and let the database do the caching of the data for you. For effective database data caching may need to make adjustments of the PostgreSQL configuration file (postgresql.conf file) as well as the operating system resources configuration. This way the response time of your client application will degrade gracefully with the increase of concurrent client requests.

For small number of concurrent connections, the speed advantage direct “streaming” solution may have over the traditional connection pooling solution may hardly be noticeable to end user. The easier way to increase response time is to look into PostgreSQL performance tuning as well as investing in faster hardware (mainly the the disk subsystem and more RAM).

Regards,

Allan.




On Wed, Sep 10, 2014 at 8:25 PM, Dmitriy Igrishin <[hidden email]> wrote:
Hello, Steve

2014-09-10 21:08 GMT+04:00 Steve Atkins <[hidden email]>:

On Sep 10, 2014, at 12:16 AM, Dmitriy Igrishin <[hidden email]> wrote:

> Hello, David
>
> 2014-09-10 4:31 GMT+04:00 David Boreham <[hidden email]>:
> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.
> For many web projects I consider Postgres as a development platform. Thus,
> I prefer to keep the business logic (data integrity trigger functions and
> API functions) in the database. Because of nature of the Web, many concurrent
> clients can request a site and I want to serve maximum possible of them with
> minimal overhead. Also I want to avoid a complex solutions. So, I believe that
> with asynchronous solution it's possible to *stream* the data from the database
> to the maximum number of clients (which possible can request my site over a
> slow connection).

That's going to require you to have one database connection open for each
client. If the client is over a slow connection it'll keep the database connection
open far longer than is needed, (compared to the usual "pull data from the
database as fast as the disks will go, then spoonfeed it out to the slow client"
approach). Requiring a live database backend for every open client connection
doesn't seem like a good idea if you're supporting many slow concurrent clients.
Good point. Thus, some of caching on the HTTP server side should be implemented
then.


--
// Dmitriy.


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Re: Async IO HTTP server frontend for PostgreSQL

John DeSoi
In reply to this post by Dmitry Igrishin

On Sep 10, 2014, at 12:02 PM, Dmitriy Igrishin <[hidden email]> wrote:

> While this is not related to the %subj%, I've glanced and the link above.
> And I found this complex. (As many many many "nice featured" things
> on the market today.) Could you tell me please, for example, why the
> URLs like

I did not write the spec, so you'll have to post to the wiki to ask questions. Just thought it might be relevant for anyone interested in this topic.

Best,

John DeSoi, Ph.D.




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Re: Async IO HTTP server frontend for PostgreSQL

Dmitry Igrishin
In reply to this post by Allan Kamau-3
Hello, Allan

2014-09-11 0:29 GMT+04:00 Allan Kamau <[hidden email]>:

Dear Dmitriy,

To add on to David's suggestions, Data caching is a difficult task to undertake. Consider an example where your data may not all fit into memory, when you cache these data outside PostgreSQL you would need to look into memory management as well as issues around concurrent population of this cache as well as means to keep the data in the cache fresh in tune with any changes to the data. These are no trivial tasks and the database community has spent years constructing and improving algorithms to do this on behalf of the front end database application developer. Also each time a TCP connection is created, additional compute resources are consumed by the OS as well as the database management server software.

Memory - limited resource. Hence, it's possible to catch "out of memory" everywhere.
By caching in this case I mean flushing the data retrieved by HTTP server from the
database server on the disk during "socket read-ready event" dispatching if the
retrieved data cannot be send to the HTTP-client (socket not write-ready yet). When
the socket to the HTTP-client became "write-ready" the data will be streamed
from cache.
I believe, it's not hard to implement it. And note, there is no need to make such
cache shared. It's just a temporary files with live time of HTTP request dispatching.

A simpler way would be to use connection pooling where a thread of your running application "borrows" a connection from a pool of open connections, executes the SQL command then returns the connection immediately on completion of the SQL command. This will require few concurrent connections (depending of configuration) and let the database do the caching of the data for you. For effective database data caching may need to make adjustments of the PostgreSQL configuration file (postgresql.conf file) as well as the operating system resources configuration. This way the response time of your client application will degrade gracefully with the increase of concurrent client requests.

In practice, this approach works. How well? It works. But with thread/connection pools
your site can be blocked by attacker ("cool-hacker") by initiating many slow
concurrent connections.
Using threads a good only if you're doing a lot of CPU work, rather than
communication work.

For small number of concurrent connections, the speed advantage direct “streaming” solution may have over the traditional connection pooling solution may hardly be noticeable to end user. The easier way to increase response time is to look into PostgreSQL performance tuning as well as investing in faster hardware (mainly the the disk subsystem and more RAM).

Yes, I agree. Good and fast hardware is always good :-). But every hardware
will has limited resources anyway. And I believe, that for many tasks async
solution will help to leverage it to the max.

Regards,

Allan.




On Wed, Sep 10, 2014 at 8:25 PM, Dmitriy Igrishin <[hidden email]> wrote:
Hello, Steve

2014-09-10 21:08 GMT+04:00 Steve Atkins <[hidden email]>:

On Sep 10, 2014, at 12:16 AM, Dmitriy Igrishin <[hidden email]> wrote:

> Hello, David
>
> 2014-09-10 4:31 GMT+04:00 David Boreham <[hidden email]>:
> Hi Dmitriy, are you able to say a little about what's driving your quest for async http-to-pg ?
> I'm curious as to the motivations, and whether they match up with some of my own reasons for wanting to use low-thread-count solutions.
> For many web projects I consider Postgres as a development platform. Thus,
> I prefer to keep the business logic (data integrity trigger functions and
> API functions) in the database. Because of nature of the Web, many concurrent
> clients can request a site and I want to serve maximum possible of them with
> minimal overhead. Also I want to avoid a complex solutions. So, I believe that
> with asynchronous solution it's possible to *stream* the data from the database
> to the maximum number of clients (which possible can request my site over a
> slow connection).

That's going to require you to have one database connection open for each
client. If the client is over a slow connection it'll keep the database connection
open far longer than is needed, (compared to the usual "pull data from the
database as fast as the disks will go, then spoonfeed it out to the slow client"
approach). Requiring a live database backend for every open client connection
doesn't seem like a good idea if you're supporting many slow concurrent clients.
Good point. Thus, some of caching on the HTTP server side should be implemented
then.


--
// Dmitriy.





--
// Dmitriy.