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niklas 2011-04-21 10:21:45 +02:00
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@ -327,18 +327,18 @@ Background
\begin_layout Standard \begin_layout Standard
The game industry is a quickly growing industry where the need for new technique The game industry is a quickly growing industry where the need for new technique
s is large. s is large.
One specific section where the development has stalled is the game server One specific section where development has stalled is the game server section.
section.
The existing game servers are functional but they lack good fault tolerance The existing game servers are functional but they lack good fault tolerance
and the ability to scale well. and the ability to scale well.
Users will notice this in low uptime and many crashes. Users will notice this in low uptime and many crashes.
This is a problem that has existed and been resolved in other industries. This is a problem that has existed and been resolved in other industries.
One good example is the telecom industry which have managed to develop One good example is the telecom industry which managed to develop solutions
solutions to similar problems. to similar problems.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
A common figure often used in telecoms is that of A common figure often used to measure the availability in telecoms is that
of
\emph on \emph on
the nine nines the nine nines
\emph default \emph default
@ -358,8 +358,8 @@ the nine nines
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The main reason to develop reliable servers are monetary, it is important The main reason to develop reliable servers are monetary as it is important
for game companies to expand its customer base. for game companies to expand their customer base.
Reliable game servers are one improvement that will create a good image Reliable game servers are one improvement that will create a good image
of a company. of a company.
In general the downtime of game servers are much higher than the downtime In general the downtime of game servers are much higher than the downtime
@ -369,8 +369,8 @@ The main reason to develop reliable servers are monetary, it is important
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
In the current state game servers is coded for each game that needs it, In the current state game servers are coded for specific games, in many
in many cases this seems like a bad solution. cases this seems like a bad solution.
Developers that want to make a network game need to understand network Developers that want to make a network game need to understand network
programming. programming.
A way to change this is a generic game server which give the game developers A way to change this is a generic game server which give the game developers
@ -421,7 +421,7 @@ key "Bondi:2000:CSI:350391.350432"
. .
These two issues are addressed in this thesis. These two issues are addressed in this thesis.
Structural scalability means expanding an architecture, e.g. Structural scalability means expanding an architecture, e.g.
adding nodes to a system, without requiring modification of the system. adding nodes to a system without requiring modification of the system.
Load scalability means using the available resources in a way which allows Load scalability means using the available resources in a way which allows
handling increasing load, e.g more users, gracefully. handling increasing load, e.g more users, gracefully.
\end_layout \end_layout
@ -461,14 +461,14 @@ A generic game server has to be able to run different client-server network
\begin_layout Standard \begin_layout Standard
The server behaves in a way similar to an application server, but is designed The server behaves in a way similar to an application server, but is designed
to help running games. to help running games.
An application server provides processing ability and time, therefore it An application server provides processing ability and time; therefore,
is different from a file- or print-server, which only serves resources it is different from a file- or print-server, which only serves resources
to the clients. to the clients.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The most common type of application servers are web servers, where you run The most common type of application servers are web servers, where the user
a web application within the server. run a web application within the server.
The application server provides an environment and interfaces to the outer The application server provides an environment and interfaces to the outer
world, in which applications run. world, in which applications run.
Hooks and helpers are provided to use the resources of the server. Hooks and helpers are provided to use the resources of the server.
@ -532,7 +532,7 @@ game development language
\begin_layout Standard \begin_layout Standard
No hard limit has been set on which languages can be used for game development No hard limit has been set on which languages can be used for game development
on the GGS, but there are several factors which decide the feasibility on the GGS, but there are several factors which decide the feasibility
of a language; of a language:
\end_layout \end_layout
\begin_layout Itemize \begin_layout Itemize
@ -653,8 +653,8 @@ ng them, a Generic Game Server should address all of them and help the developer
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Due to the limited capability of threading in many GDL VM:s, the GGS prototype Due to the limited capability of threading in many GDL VMs, the GGS prototype
will not support MMORPG:s as it is not possible to implement and test something will not support MMORPGs as it is not possible to implement and test something
that complex within the projects timetable. that complex within the projects timetable.
\end_layout \end_layout
@ -709,14 +709,13 @@ name "cha:Theory"
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
In this chapter, the theory behind the techniques used in the GGS are discussed In this chapter, the theory behind the techniques used in the GGS are discussed.
here. Performance issues and the measuring of performance are discussed.
Performance issues and the measuring of performance is discussed. Benchmarking techniques are discussed.
Benchmarking techniques are discusses. The options when choosing network protocols are given, along with advantages
The options when choosing network protocols are given, along with pros and disadvantages for each of the alternatives.
and cons for each of our alternatives. Finally, an overview of scalability, fault tolerance and availability is
Finally, a bird's eye-view of scalability, fault tolerance and availability presented.
is presented.
\end_layout \end_layout
\begin_layout Section \begin_layout Section
@ -920,11 +919,11 @@ Fault Tolerance
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Fault tolerance is an important factor in all servers, a server that is Fault tolerance is an important factor in all servers; a server that is
fault tolerant should be able to follow a given specification when parts fault tolerant should be able to follow a given specification when parts
of the system failures. of the system failures.
This means that fault tolerance is different in each system depending on This means that fault tolerance is different in each system depending on
what specification they have. what specification the system have.
A system could be fault tolerant in different aspects, one is where the A system could be fault tolerant in different aspects, one is where the
system is guaranteed to be available but not safe and it could also be system is guaranteed to be available but not safe and it could also be
reversed, that the system is safe but not guaranteed to be available. reversed, that the system is safe but not guaranteed to be available.
@ -953,11 +952,11 @@ In order to make the GGS prototype fault tolerant the programming language
\begin_layout Standard \begin_layout Standard
The need for fault tolerance in game servers is not as obvious as it may The need for fault tolerance in game servers is not as obvious as it may
be for other typ of servers. be for other types of servers.
In general all servers strive to be fault tolerant as fault tolerance means In general all servers strive to be fault tolerant as fault tolerance means
more uptime and a safer system. more uptime and a safer system.
This applies to game servers aswell, in brief good fault tolerance is a This applies to game servers as well, in brief good fault tolerance is
way of satisfying customers. a way of satisfying customers.
In general, game servers differ from many other fault tolerant systems In general, game servers differ from many other fault tolerant systems
in that high-availability is more important than the safety of the system. in that high-availability is more important than the safety of the system.
For example a simple calculation error will not be critical for a game For example a simple calculation error will not be critical for a game
@ -978,8 +977,8 @@ Availability
\begin_layout Standard \begin_layout Standard
One important factor of any server is the availability. One important factor of any server is the availability.
A server to which you are unable to connect to is a useless server. A server to which you are unable to connect to is a useless server.
Other then within telecomunication, their uptime is of about 99,9999999%, Other then within telecommunication, their uptime is of about 99,9999999%,
the game developer community hasn't approched this problem very genuinely the game developer community hasn't approached this problem very genuinely
yet so there is much room for improvement. yet so there is much room for improvement.
\end_layout \end_layout
@ -1036,7 +1035,7 @@ Each instance of the GGS contains several tables.
down at a new table, all within the same game session. down at a new table, all within the same game session.
With this in mind, the main focus of the GGS is not to move players between With this in mind, the main focus of the GGS is not to move players between
tables, but to keep a player in a table, and to start new tables instead. tables, but to keep a player in a table, and to start new tables instead.
When a server has reached a certain amount of players the performance will When a server has reached a certain number of players the performance will
start to decrease. start to decrease.
To avoid this the GGS will start new tables on another server, using this To avoid this the GGS will start new tables on another server, using this
technique the players will be close to evenly distributed between the servers. technique the players will be close to evenly distributed between the servers.
@ -1482,7 +1481,7 @@ end{centering}
status open status open
\begin_layout Plain Layout \begin_layout Plain Layout
Add clients on each side, and replace the cloud with phole-landlines being Add clients on each side, and replace the cloud with pole-landlines being
cut by a pair of scissors cut by a pair of scissors
\end_layout \end_layout
@ -1519,7 +1518,7 @@ Security
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
We only support languages running in a sandboxed environment. The project only support languages running in a sandboxed environment.
Each game session is started in its own sandbox. Each game session is started in its own sandbox.
The sandboxing isolates the games in such a way that they can not interfere The sandboxing isolates the games in such a way that they can not interfere
with each other. with each other.
@ -1544,11 +1543,11 @@ Game Development Language in a Virtual Machine
There is only a very limited number of game developers who would like to There is only a very limited number of game developers who would like to
write their games in Erlang, therefore we had to come up with something write their games in Erlang, therefore we had to come up with something
to resolve this problem. to resolve this problem.
The main idea was to offer a replacable module which would introduce a The main idea was to offer a replaceable module which would introduce a
interface to different virtual machines which would run the game code. interface to different virtual machines which would run the game code.
This way a game developer can write the game in his favourite language This way a game developer can write the game in his favorite language while
while the server part still is written in Erlang and can benefit from all the server part still is written in Erlang and can benefit from all of
of its advantages. its advantages.
\end_layout \end_layout
\begin_layout Subsection \begin_layout Subsection
@ -1710,7 +1709,7 @@ number of clients
\end_layout \end_layout
\begin_layout Chapter \begin_layout Chapter
Practice Implementation
\begin_inset Note Note \begin_inset Note Note
status collapsed status collapsed
@ -1740,10 +1739,10 @@ implementation
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
This chapter contains the realization of much of the principles and techniques This chapter contains the realization of many of the principles and techniques
described in chapter described in chapter
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand vref LatexCommand ref
reference "cha:Theory" reference "cha:Theory"
\end_inset \end_inset
@ -1854,7 +1853,7 @@ In Erlang, we have a simple version of supervisors.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
When the linking of processes in order to monitor exit behaviour is coupled When the linking of processes in order to monitor exit behavior is coupled
with the transparent distribution of Erlang, a very powerful supervision with the transparent distribution of Erlang, a very powerful supervision
system is created. system is created.
For instance, we can restart a failing process on a different, new node, For instance, we can restart a failing process on a different, new node,
@ -1863,7 +1862,7 @@ When the linking of processes in order to monitor exit behaviour is coupled
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
In the GGS, we have separated the system in to two large supervised parts. In the GGS, we have separated the system into two large supervised parts.
We try to restart a crashing child separately, if this fails too many We try to restart a crashing child separately, if this fails too many
\begin_inset Foot \begin_inset Foot
status collapsed status collapsed
@ -2018,20 +2017,20 @@ erlang_js
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
To be able to run JavaScript on our server we needed to embed a JavaScript To be able to run JavaScript on the server there was a need to embed a JavaScrip
engine within the server. t engine within the server.
After a thorough investigation erlang_js became our choice. After a thorough investigation erlang_js became the choice.
Erlang_js provides direct communication with a JavaScript VM (Virtual Machine). Erlang_js provides direct communication with a JavaScript VM (Virtual Machine).
This was exactly what we wanted, but we also needed the possibility to This was exactly what was wanted, but there was also a need to communicate
communicate from erlang_js to Erlang. from erlang_js to Erlang.
This functionality was not yet implemented in erlang_js, due to lack of This functionality was not yet implemented in erlang_js, due to lack of
time. time.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
There were two possible solutions to the problem. There were two possible solutions to the problem.
We could rewrite some part of erlang_js, or we could switch erlang_js for To rewrite some part of erlang_js, or to switch erlang_js for some other
some other JavaScript engine. JavaScript engine.
Searching for other engines we found erlv8 and beam.js which provided the Searching for other engines we found erlv8 and beam.js which provided the
functionality that we wanted. functionality that we wanted.
As we tested beam.js it occurred random crashes of the whole Erlang environment. As we tested beam.js it occurred random crashes of the whole Erlang environment.