Open Enterprise: The PostgreSQL Open Source Database Blog from EnterpriseDB

Postgres 9.2 Draft Release Note Published

Bruce Momjian — Thu, 10 May 2012 10:45:01 +0000

I have completed the Postgres 9.2 release notes I started seven days ago. Writing the release notes is always a taxing experience. I have to basically dedicate an entire week to the process of digesting 1100 commit messages to produce 3000 lines of SGML text. Once I am done though, it is rewarding to see the finished product. It is like working on a painting all year, and spending a frustrating week framing it and hanging it on the all — once it is hung, you stand and admire it, and forget much of the sweat it took to produce. I am sure many community members feel the same.

Curious about how the 9.2 release item count compares to previous major releases? Here are the results:

Release	Items
9.2	245
9.1	213
9.0	252
8.4	330
8.3	237
8.2	230
8.1	187
8.0	238
7.4	280

Postgres Drinking Game

EnterpriseDB — Mon, 07 May 2012 12:00:01 +0000

My children have traveled to many conferences with me, and have heard many webcasts and training calls at home. I guess, after hearing about Postgres so often, they pick up certain phrases of interest, and the big one for them is “shared buffers”. Anytime someone uses those words, they start howling and make up some funny sentence using the words.

There are a variety of beer drinking games that trigger drinking when a word is said — perhaps “shared buffers” is enough on its own to make a drinking game.

The Effectiveness of effective_cache_size

Bruce Momjian — Fri, 04 May 2012 08:30:01 +0000

Having reported the methods for finding the size of the kernel cache on Linux, I wish to highlight the importance of the postgresql.conf setting
effective_cache_size.

Unlike other memory settings that control how memory is allocated, effective_cache_size tells the optimizer how much cache is present in the kernel. This is important for determining how expensive large index scans will be. The optimizer knows the size of shared_buffers, but not the kernel cache size, which affects the probability of expensive disk access.

Starting on 9.2 Release Notes

Bruce Momjian — Thu, 03 May 2012 10:00:01 +0000

As in previous years, I have started working on major release notes, this time for Postgres 9.2. I start with this command:

$ src/tools/git_changelog --since '2011-06-11 00:00:00 GMT' --master-only \
> --oldest-first --details-after

Measuring Free Memory and Kernel Cache Size on Linux

Bruce Momjian — Wed, 02 May 2012 10:00:01 +0000

Measuring Linux free memory and kernel cache size can be somewhat tricky. You might look at /proc/meminfo for the answer (commas added):

# cat /proc/meminfo
MemTotal:       24,736,604 kB
MemFree:         3,805,392 kB
Buffers:           743,016 kB
Cached:         18,188,208 kB
...

Caching Levels

Bruce Momjian — Mon, 30 Apr 2012 10:30:01 +0000

There are several levels of caching used in a typical server — here they are, in order of increasing distance from the cpu:

1.	Cpu cache
2.	Random-Access Memory (RAM)
3.	Storage controller cache
4.	Storage device (disk) cache

All of these are a fixed size and set at hardware installation time, i.e. you can’t move cache from one level to another. For Postgres, there is flexibility in how #2, random-access memory, is allocated, and this provides a never-ending opportunity for administrators to optimize their systems. The three RAM allocation possibilities are:

shared_buffers
work_mem
Kernel cache

Upcoming Events

Bruce Momjian — Sat, 28 Apr 2012 10:15:01 +0000

During the next two months I will be attending events in the following cities: New York City, Ottawa, Charlotte (North Carolina), and Boston — the details are on my website. I will also be doing training in many of these locations. And I spoke in Philadelphia this week — I guess this is what the New Postgres Era looks like.

Why Use Multiple Schemas?

Bruce Momjian — Fri, 27 Apr 2012 11:15:01 +0000

I mentioned that Postgres supports multiple clusters, databases, and schemas, but an open question is why use multiple schemas, rather than placing everything in the “public” schema? By default, search_path places everything in the public schema (assuming a schema matching the current user name does not exist):

test=> SHOW search_path;
  search_path
----------------
 "$user",public
(1 row)

Take a Dip in the Pooler

Bruce Momjian — Wed, 25 Apr 2012 10:15:01 +0000

I recently mentioned the use of connection poolers to reduce the overhead of server-side language initialization, but I believe the topic warrants fuller coverage.

Aside from the ability to reduce language initialization overhead, the two major advantages of connection pooling are:

Reducing session startup time by preallocating and reusing database sessions
Reducing session management overhead by reducing the number of idle sessions

Tour: PPCD Running on HP

Bobby Bissett — Mon, 23 Apr 2012 15:14:00 +0000

The HP Compute Cloud will be starting its public beta soon, and the Postgres Plus Cloud Database will be there. You can see a tour now of the user console running on HP.

We’re excited to start offering the cloud database on more and more service providers.