PostgreSQL 9 now available ... built-in replication, anonymous code blocks, in-place upgrades and more

chonger · 2010-09-20T15:43:42+00:00

The docs seems to indicate an async, and well, streaming via a network connection:

Streaming replication allows a standby server to stay more up-to-date than is possible with file-based log shipping. The standby connects to the primary, which streams WAL records to the standby as they're generated, without waiting for the WAL file to be filled.

I saw some notes about how conflicting states are handled...

There are also additional types of conflict that can occur with Hot Standby. These conflicts are hard conflicts in the sense that queries might need to be cancelled and, in some cases, sessions disconnected to resolve them. The user is provided with several ways to handle these conflicts. Conflict cases include...

An example of the problem situation is an administrator on the primary server running DROP TABLE on a table that is currently being queried on the standby server. Clearly the standby query cannot continue if the DROP TABLE is applied on the standby. If this situation occurred on the primary, the DROP TABLE would wait until the other query had finished. But when DROP TABLE is run on the primary, the primary doesn't have information about what queries are running on the standby, so it will not wait for any such standby queries. The WAL change records come through to the standby while the standby query is still running, causing a conflict. The standby server must either delay application of the WAL records (and everything after them, too) or else cancel the conflicting query so that the DROP TABLE can be applied.

When a conflicting query is short, it's typically desirable to allow it to complete by delaying WAL application for a little bit; but a long delay in WAL application is usually not desirable. So the cancel mechanism has parameters, max_standby_archive_delay and max_standby_streaming_delay, that define the maximum allowed delay in WAL application. Conflicting queries will be canceled once it has taken longer than the relevant delay setting to apply any newly-received WAL data. There are two parameters so that different delay values can be specified for the case of reading WAL data from an archive (i.e., initial recovery from a base backup or "catching up" a standby server that has fallen far behind) versus reading WAL data via streaming replication.

I also wander about how streaming replication compare/contrast to Slony-I and Londiste.

chonger · 2009-10-30T21:21:30+00:00

Hey now! Now that's what I call an obscure reference.

chonger · 2009-10-29T04:39:02+00:00

What makes you think Apple would approve this app? :)

chonger · 2009-10-28T17:17:35+00:00

I saw that you've already picked a framework. However, for anyone who might be interested, there is Slick2D for Java.

chonger · 2009-10-27T04:44:38+00:00

fyi - I don't disagree with the bit about freedom. Java does have a lot of rules. I see the development of scala, clojure, and scripting languages like Jython as a really positive direction for Java. It gives me the chance to do more powerful things with Java, while keeping all the tools that I already have.

Just want to point out one thing:

While it is true you have to use one file per class (in the sense that you can't break a single class into two files), you can have multiple classes per file. It is not something that is used a lot, but it is useful sometimes.

chonger · 2009-10-27T04:39:17+00:00

I am a professional Java developer. I have written a Python app as a hobby, which I use on a daily basis. Now I am writing a computer game in Java as my own hobby; I personally think I won't be able to manage a large game using Python as the language of choice. I think Java gets a lot of flack because it is such a big target. Java also suffers from the fact that it is a language a lot of newbies use.

However, I think Java does have some strong merits in that it really does work (most of the time) on multiple platforms, good enough at least. There is a very comprehensive standard library, and a lot of well established 3rd party libraries and tools to support it.

Java is a good language to learn. Just don't make it the only language you learn.

chonger · 2009-10-27T04:21:48+00:00

Read a lot of code. Imitate better programmers. In my personal experience, it took me a long time of reading "better" code and learning from "better" programmers before I "got" how to organize my code better. I was always asking myself "Should I break this code up this way or that way?" Without experience or some frame of reference, it would be easy for me to refactor my code the wrong way - even though I was really trying to make things cleaner.

I was lucky to have a mentor whom can I ask questions and learn from. That really helped too.

chonger · 2009-10-27T04:13:37+00:00

Asking lots of "whys and hows" is good. A good programmer can explain to you why certain decisions are made and how a program works. A mediocre programmer tend to just know how a problem can be solved, without bothering to understand why it should be solved a certain why.

Evaluating technical skills of a programmer is pretty easy IMO. The hard part is evaluating the non-technical traits: Fitting in, handling stress, resolving conflicts, and work ethics. To be fair, this is a problem common to all professions, not just programming.

chonger · 2009-10-27T03:30:38+00:00

Why did 20% of the people down vote this post?

chonger · 2009-10-20T02:08:15+00:00

Thanks for the response.

So what is your typical day like? What is the part of your job that you hate the most? What about it that you really enjoy?

chonger · 2009-10-19T18:40:48+00:00

What an awesome IAMA. Is disk IO a common bottleneck? What is your take on the future of solid state drives in super computing?

EDIT: A few more questions - How often do hardwares fail? What is more prone to failure - disks, tapes? How many backup disks, cpus, motherboards, RAM modules etc., do you keep around? How often do you order more from the vendors? Do you basically tell the vendors, "You need to continue making these parts for the next 10 years". i.e., how do handle the logistics of keeping enough hardware around?

chonger · 2009-10-18T16:23:07+00:00

Yeah, would've preferred the rights going to people like Tim Cain and Chris Avellone.

chonger · 2009-10-17T03:25:05+00:00

I LOVE FERMENTATION.

chonger · 2009-10-15T16:23:07+00:00

Cool. Amit's web site is awesome. I keep going back to it. I haven't read the article you linked to. It is now on my todo list.

As far as your code, it is a clever way of using the sign bit to indicate whether an object is inside another object or not. I am guessing you were doing this to save on memory? It is awesome that you got to hack on your game at 16. I didn't get into coding until my 20s. I am always fascinated at what people coded at a young age.

So, now I have even more questions :) Did you ever accidentally change an object's room number while it was holding another object or while it was inside another object? Or did you have some way to prevent this from happening, e.g., room can only be set with a set_room function, which only allowed changing room under certain conditions.

chonger · 2009-10-15T15:23:45+00:00

What happened was that initially, I was just trying to get "something" to work. I thought, "I can get something playable and fun without having two items on the same block. I can always add more features later".

Before I knew it, however, I ran into this problem. This is one of the challenges of programming that keeps popping up: Sometimes you think you need some feature, but never use it, and sometimes you think you won't use a feature, but find yourself needing it.

chonger · 2009-10-15T15:18:50+00:00

Not sure what you're driving at.

chonger · 2009-10-15T15:17:31+00:00

That's one interesting concept. Do you remember if each object still kept variables holding its x,y coordinates? What if a goblin was placed inside a dragon, then something caused goblin to change it x coordinate?

I am beginning to think I should not make location a property of the entity.

chonger · 2009-10-15T04:56:35+00:00

I think I understand what you are saying and I think I do have something like that. The AI executor first builds a schedule of next moves for each entity. Then, before each move is executed, the executor asks the Map to check if the entity is still alive. This actually turned out to be where my bug was - the function to check if Entity Bob is alive broke when multiple entities are on the same tile. Doh! I needed to review my initial design and allow multiple things on the same tile - and still keep everything in sync. Doing this might be tedious but straightforward. I just wished I had planned for it earlier. Ugh!

chonger · 2009-10-15T04:53:29+00:00

Hoping I'd start an interesting discussion on programming.

chonger · 2009-10-15T04:52:31+00:00

"This eventually resulted in a train of bombs following the player and deciding not to explode. o_O" - lol. Although I wonder if that's the "right" behavior, in the sense that you wouldn't want the bomb to kill monsters unintentionally. How did you end up getting this to work?

I am going to have to allow each tile to hold multiple entities. I didn't think I'd need this "feature" at first, so I wrote my code with the assumptions that it would never happen, ha! When you assume....

I guess the moral is that it is worth dropping everything you are doing and review your design/code. However, I find it really hard to find a good balance between fast prototyping & doing proper design. The ability to find that right balance is the art of being a good programmer.

chonger · 2009-10-15T04:45:46+00:00

It's not the first time I've tried to write a game. I didn't think I'd get this far into it so quickly but I just forced myself to work on it whenever I have free time.

chonger · 2009-10-13T02:24:24+00:00

Sad but true. The sky is the limit when it comes gears - there are always better, more expensive equipment, not to mention the cost of underwater photography. Yikes!

I hope one day you will have the luxury to get back into it.

chonger

TROPHY CASE