= libpsyc Performance Benchmarks =

In this document we present the results of performance benchmarks
of libpsyc compared with libjson-glib and libxml2.

== Procedure ==

We'll use typical messages from the XMPP ("stanzas" in Jabber
lingo) and compare them with equivalent JSON encodings,
verbose and compact PSYC formats.

In some cases we will additionally compare PSYC packets to
a more efficient XML encoding based on PSYC methods, to have
a more accurate comparison of the actual PSYC and XML
syntaxes, rather than the protocol structures of PSYC and XMPP.

== The Benchmarks ==

=== A presence packet ===

Since presence packets are by far the dominant messaging content
in the XMPP network, we'll start with one of them.
Here's an example from paragraph 4.4.2 of RFC 6121.

{{{
<presence from='juliet@example.com/balcony'
            to='benvolio@example.net'>
	<show>away</show>
</presence>

}}}

And here's the same information in a JSON rendition:

{{{
["presence",{"from":"juliet@example.com/balcony","to":"benvolio@example.net"},{"show":"away"}]
}}}

Here's the equivalent PSYC packet in verbose form
(since it is a multicast, the single recipients do not
need to be mentioned):

{{{
:_context	psyc://example.com/~juliet

=_degree_availability	4
_notice_presence
|
}}}

And the same in compact form:

{{{
:c	psyc://example.com/~juliet

=da	4
np
|
}}}

=== An average chat message ===
=== A social network activity ===
=== A message with JSON-unfriendly characters ===
=== A message with XML-unfriendly characters ===
=== A packet containing a JPEG photograph ===

=== A random data structure ===

In this test we'll not consider XMPP at all and simply compare the
efficiency of the three syntaxes at serializing a typical user data base
storage information. We'll again start with XML:

{{{
<UserProfile>
    <Name>Silvio Berlusconi</Name>
    <JobTitle>Premier</JobTitle>
    <Country>I</Country>
    <Address>
	    <Street>Via del Colosseo, 1</Street>
	    <PostalCode>00100</PostalCode>
	    <City>Roma</City>
    </Address>
    <Page>http://example.org</Page>
</UserProfile>
}}}

In JSON this would look like this:

{{{
["UserProfile",{"Name":"Silvio Berlusconi","JobTitle":"Premier","Country":"I","Address":
{"Street":"Via del Colosseo, 1","PostalCode":"00100","City":"Roma"},"Page":"http://example.org"}]
}}}

Here's a way to model this in PSYC:

{{{
:_name	Silvio Berlusconi
:_title_job	Premier
:_country	I
:_address_street	Via del Colosseo, 1
:_address_code_postal	00100
:_address_city	Roma
:_page	http://example.org
_profile_user
|
}}}

== Conclusions ==

== Criticism ==

Are we comparing apples and oranges? Yes and no, depends on what you
need. XML is a syntax best suited for complex structured data in
well-defined formats - especially good for text mark-up. JSON is a syntax
intended to hold arbitrarily structured data suitable for immediate
inclusion in javascript source codes. The PSYC syntax is an evolved
derivate of RFC 822, the syntax used by HTTP and E-Mail, and is therefore
limited in the kind and depth of data structures that can be represented
with it, but in exchange it is highly performant at doing just that.

So it is up to you to find out which of the three formats fulfils your
requirements the best. We use PSYC for the majority of messaging where
JSON and XMPP aren't efficient and opaque enough, but we employ XML and
JSON as payloads within PSYC for data that doesn't fit the PSYC model.
For some reason all three formats are being used for messaging, although
only PSYC was actually designed for that purpose.

== Caveats ==

In every case we'll compare performance of parsing and re-rendering
these messages, but consider also that the applicative processing
of an XML DOM tree is more complicated than just accessing
certain elements in a JSON data structure or PSYC variable
mapping.

For a speed check in real world conditions which also consider the
complexity of processing incoming messages we should compare
the performance of a chat client using the two protocols,
for instance by using libpurple with XMPP and PSYC accounts.
To this purpose we first need to integrate libpsyc into libpurple.