July 2010

１．書き込みキャッシュ
Write Cacheがパフォーマンスに及ぼす影響は今回のテストで分かった。
また、揮発性のWrite Cacheだけの書き込みがブロック障害の原因になる可能性もあるということも気になる。
しかし、それを言っているときりがない。HDD自体にもWrite Cacheはあるのだから

今回のディスク　WD6000HLHX

32 MB キャッシュ　　　600 GB,SATA 6 Gb/s,10,000 RPM

同タイプでRAID用「高ストライピング前提」「少Write Cacheタイプ」のモデルもある
WD3000BLFS　　16 MB キャッシュ　　　300 GB,SATA 3 Gb/s,10,000 RPM
→だから容量が少ない。だから安全性優先でWrite Cacheが少ない。

２．読み込みキャッシュ

ハイブリッド型RAIDカードタイプ
Adaotec社HPより

アダプテックMaxIQ SSD キャッシュ - 8倍のIO/秒
アダプテックMaxIQ SSDキャッシュソフトウェアは、最高のリードパフォーマンスを発揮するために、読み出し頻度の高い（「ホット」)データを見分けて、このデータをSSDキャッシュ内にコピーする特許出願中の「ラーンドパス」アルゴリズムを導入しています。

SSD in HDDタイプ　　シーゲイト Momentus® XT ドライブ
シーゲートHPより

Here’s an example of how you have to think about conflicts of interest when dealing with problems of scalability. It starts with a request (that I won’t give in detail, and was a little different from the shape I describe below)  from a client for advice on how to make a query go faster. Basic [...]

Being triggered by Laurent Schneider’s post “extract xml from the command line“; I completely forgot about the C-based XDK tooling you nowadays can find in your $ORACLE_HOME. You, probably just like me, weren’t even aware, there were some (C-based that is). Most of these are executable’s and not “just” Java tools, although xsql is a shell script that still starts Java. More information can be found here in the “Oracle® XML Developer’s Kit Programmer’s Guide 11.2”

I mean in principle they are not “new”, they were there since 8.1.x, but now they are compiled executables which you can use on the shell prompt and or in scripting and that is, at least for me, easier than doing the same via their $ORACLE_HOME/xdk Java counterparts.

A shortlist:

(This post originally appeared at the Pythian blog)

I’ve been following the discussion in various MySQL blogs regarding the sort_buffer_size parameters. As an Oracle DBA, I don’t have an opinion on the subject, but the discussion did remind me of many discussions I’ve been involved in. What’s the best size for SDU? What is the right value for OPEN_CURSORS? How big should the shared pool be?

All are good questions. Many DBAs ask them hoping for a clear cut answer – Do this, don’t do that! Some experts recognize the need for a clear cut answer, and if they are responsible experts, they will give the answer that does the least harm.