For the last couple of months, we've been quietly developing a MySQL protocol parser for Maatkit. It isn't an implementation of the protocol: it's an observer of the protocol. This lets us gather queries from servers that don't have a slow query log enabled, at very high time resolution.

With this new functionality, it becomes possible for mk-query-digest to stand on the sidelines and watch queries fly by over TCP. It is only an observer on the sidelines: it is NOT a man in the middle like mysql-proxy, so it has basically zero impact on the running server (tcpdump is very efficient) and zero impact on the query latency. There are some unique challenges to watching an entire server's traffic, but we've found ways to solve those. Some of them are harder than others, such as making sense of a conversation when you start listening in the middle. In general, it's working very well. We can gather just about every bit of information about queries that mysql-proxy can, making this a viable way to monitor servers without the disadvantages of a proxy. In theory, we can gather ALL the same information, but in practice we are going for the 95% case.

As always with Maatkit, this has minimal dependencies. It doesn't require any Net::Pcap or other modules from CPAN. It's written in pure Perl, and it parses the output of tcpdump, rather than watching the network traffic directly. This might sound useless, but it's not. It means you can go tcpdump some traffic on a machine without Perl installed, and copy it to another machine for analysis, or send it via email to your friendly consultant, or do any of a number of other things. Decoupling things is very helpful sometimes.

Let's see how to gather queries and do something useful with them. I'll just watch the queries on a sandbox server on my laptop, and print out the profile synopsis so you can see how it works.

I run a few queries, quit, and cancel tcpdump. Now I've got a file and I'm ready to analyze it. Let's see:

I'm kind of showing off the summary profile here to illustrate that you can get really compact results to see what's going on inside your server. What do you suppose that one query was that took a tenth of a second? We can find out.

Indeed, it's no surprise the query took a tenth of a second to execute, and now you see where "SELECT dual" comes from.

Notice that it is inspecting the protocol enough to see the flags set in the protocol, indicating the warning count, error count, rows affected, and whether no index or no good index was available. Look at the top of the report -- what is up with the 12% of queries that say No_index_used? If we increase --limit a bit, we can see

I did not know that SHOW DATABASES sets the "no index used" flag, did you? Now we both do!

This is just a brief introduction to what the protocol parser can do. Of course, in real life it's much more useful than just seeing a query or two -- it has all the power of mk-query-digest for filtering, aggregating, printing and so forth.

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©作者：eygle 发布在 eygle.com

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> select * from v$sgainfo where name in ('Fixed SGA Size','Redo Buffers','Granule Size');

NAME                                  BYTES RES
-------------------------------- ---------- ---
Fixed SGA Size                      1267212 No
Redo Buffers                       15507456 No
Granule Size                       16777216 No

SQL> select sum(bytes)/1024/1024 from v$sgainfo where name in ('Fixed SGA Size','Redo Buffers');

SUM(BYTES)/1024/1024
--------------------
            15.99757

SQL> select * from v$sgainfo where name in ('Fixed SGA Size','Redo Buffers','Granule Size');

NAME                                  BYTES RES
-------------------------------- ---------- ---
Fixed SGA Size                      1263320 No
Redo Buffers                        7122944 No
Granule Size                        4194304 No

SQL> select sum(bytes)/1024/1024 from v$sgainfo where name in ('Fixed SGA Size','Redo Buffers');

SUM(BYTES)/1024/1024
--------------------
          7.99776459

With dynamic SGA, the unit of allocation is called a granule. Components, such as the buffer cache, the shared pool, the java pool, and the large pool, allocate and free SGA space in units of granules. Oracle tracks SGA memory use in integral numbers of granules, by SGA component. All information about a granule is stored in a corresponding granule entry. Oracle maintains the state of each granule in the granule entry and the granule type.

Granule size is determined by total SGA size. On most platforms, the size of a granule is 4 MB if the total SGA size is less than 128 MB, and it is 16 MB for larger SGAs. There may be some platform dependency, for example, on 32-bit Windows NT, the granule size is 8 MB for SGAs larger than 128 MB.

The granule size that is currently being used for SGA can be viewed in the view V$SGA_DYNAMIC_COMPONENTS. The same granule size is used for all dynamic components in the SGA.

Note: If you specify a size for a component that is not a multiple of granule size, then Oracle rounds the specified size up to the nearest multiple. For example, if the granule size is 4 MB and you specify DB_CACHE_SIZE as 10 MB, you will actually be allocated 12 MB.

Oracle keeps information about the components and their granules in a scoreboard. For each component that owns granules, the scoreboard contains the number of granules allocated to the component, any pending operations against this component, the target size in granules, and the progress made toward the target size. The start time of the operation is also logged. Oracle maintains the initial number of granules and the maximum number of granules for each component.

For operations that modify the number of granules, Oracle logs the operation, the target size, and the start time to the appropriate SGA component in the scoreboard. Oracle updates the progress field until the operation is complete. When the operation is complete, Oracle replaces the current size with the target size and clears the target size field and the progress field. At the end of the operation, a database administrator can see how the number of granules was changed. Oracle updates the initialization parameter values to reflect the updated amount of SGA in use.

Oracle maintains a circular buffer of the last 100 operations made to the scoreboard. Fixed views show the state of the scoreboard and the current contents of last 100 operations to the scoreboard.

Allocating Granules at Startup

At startup, Oracle reads the values in the initialization parameter file, queries the operating system memory limits, and allocates virtual address space for the SGA. The initialization parameter SGA_MAX_SIZE specifies the maximum size of the SGA for the life of the instance in bytes. Its value is rounded up to the next granule size.

Adding Granules to Components

A database administrator grows a component's SGA use with ALTER SYSTEM statements to modify the initialization parameter values. Oracle takes the new size, rounds it up to the nearest multiple of 16MB, and adds or takes away granules to meet the target size. Oracle must have enough free granules to satisfy the request. If the current amount of SGA memory is less than SGA_MAX_SIZE, then Oracle can allocate more granules until the SGA size reaches SGA_MAX_SIZE.

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作者：Fenng 发布在 dbanotes.net.

金庸小说中的美女? 这可能是一个比较老的话题了。如果"到Google上百度一下"，能找到不下百万条的记录结果。之所以会有这么多结果，可能和每个读者心目中的理想美女标准不一吧。

尽管是个老掉牙的话题，考虑到公司(注：阿里巴巴集团)崇尚武侠文化，所以唠叨几句，再做点普及可能也不算过时。有些人物形象，比如黄蓉小龙女等已是深入人心，再此略过不表。再者，美与不美是相对的，比如《《天龙八部》中的怪人包不同就觉得自己女儿包不靓最美嘛。

小昭

小昭是金庸最喜欢的女性人物。其容貌"双目湛湛有神，修眉端鼻，颊边微现梨涡，直是秀美无伦"，我们又从文中得知小昭生父韩千叶系中土人士，其母黛绮丝人家还是波斯的圣女，居然是个混血儿，考虑到遗传因素，所以美貌自不待言，比一般的美女更美也是情理之中的事情。

小昭武功不弱，聪明伶俐，通音律，且精通奇门八卦之术，绿柳庄外曾救得群雄性命，从这一点来看，人家是个完美的知识女性，用现在的话说，那叫知性美女。小昭对爱情忠诚，富有牺牲精神，最后为了张无忌而痛心远走波斯，这是颇为读者神伤的一段。

小昭恐怕也是金庸先生心目中的理想女性的化身，另外一个和她人物形象有点重叠的是双儿，当然，双儿更多了一点温柔（所以能得圆满?）。类似的女性人物形象在金庸作品中出现两次，可见作者心目中的理想美女亦相去不远。暗自揣测，这两个人物形象或许是参照金庸第三任妻子林乐怡而写的，当然这个一家之言，还有待考证。

小昭堪称金庸小说中的绝顶佳人。不知道是否有武侠小说迷按照这个标准寻找意中人的，哈哈。

郭襄

《神雕侠侣》中的郭襄，是金庸所有小说中最具亲和力的人物，"潇洒如诗"，也是金庸所有小说中最闪亮的配角人物，一见难忘，所以让何足道与张三丰"为君沉吟"。

痴情者如郭襄者，少见又少见。"天涯思君不敢忘"，一遇杨过误终身，爱慕杨过而不可得，杨过喜欢的那句话"世间不如意者，十居七八"倒应在了她身上。不是有人说了么，"得不到的东西最美好"，如果郭襄真的能和杨过在一起，反而未必那么圆满，"得不到的东西最美好"，但愿如此。郭襄这样的女子当今社会怕是没有了----都直接当小三去了。顺便说一下，郭襄的徒孙周芷若是金庸小说中相当令人生厌的人物，从某种角度上看，不亚于康敏。

王语嫣家族女性

看来遗传因素决定了一切，王语嫣一家的女性貌似都貌美得不得了。好像只有他妈王夫人稍微差了一点，估计隔代遗传的因素作怪吧。容貌归容貌，这个家族的人物性格并不讨人喜欢。

在最近新修版的《天龙八部》中，王语嫣的人物形象较之先前有了较大改变，最后热衷寻求长生不老之术，幻想青春永驻。个人认为，这是金庸小说中体现的西方神话形象那西塞斯（Narcissus）的女性版。以王语嫣为代表的女性可能是美女，但非常无趣。如果段誉娶了这样的媳妇，绝对糟糕透顶。王语嫣可算上美女，但无论如何不是佳人。

冯蘅

这是一个必须一提的人物。也是个相对比较陌生的名字，冯蘅是谁? 黄蓉她妈，黄药师的妻子。

仅仅通过其他人物的口中就已经能够得知绝代风貌，且不说黄药师如此另类人物被其折服，其过目不忘之能也当世少有，令人心驰神往，原来美貌与智慧是可以并存的。考虑到黄蓉同学多少只是他母亲的影子，加上大家太熟悉这个角色，不复赘言。

新修版中居然情节更改为黄药师因为弟子们说闲话而斗气娶了冯蘅，实在是大煞风景。这个变动相当的蛇足。

程灵素

金庸先生书中女主人公绝大多数都算美女，但程灵素除外。"头发稀疏，肌肤枯黄，脸有菜色"，如果分析一下，可能是这个古代化学专家整天接触药石之故，如果放到现在，人家就是个化学兼医学双料女博士，外表不美，心灵美，这也顶顶重要。其实内在美重要,还是外在美重要，不同的历史时期人们的价值取向也是不同的，也或许有人喜欢程灵素也说不定。

程灵素最后为胡斐牺牲，不由得让人埋怨作者下笔残酷，如果武侠小说允许假设，那么胡斐娶了程灵素是不会让人感到意外的。

香香公主

香香公主之美，美到不够真实，而其不谙世事，也似乎不是凡间之人。激战双方的兵士见到她居然"便似中邪昏迷一般，人人都呆住了...无数长矛都掉下地来，弓箭手的弓矢也收了回来...人人神色和平，收刀入鞘"，如果在今天，维护世界和平旧靠她了:) 塑造这个小说人物的时候恐怕也多少投射了一些西方经典美女海伦的有关因素在里面吧。

金庸早期小说人物形象多半缺乏立体感，香香公主也是如此，甚至在同一部小说中，还不如霍青桐更能赢得人好感。

陈圆圆

当然，香香公主再美，可能还敌不过陈圆圆，陈圆圆有多美，无法形容(所以不可能留下'西施捧心'之类的形象给世间人)！因为无法形容，所以作者描写陈圆圆多用映衬笔法，纵观全部金庸小说，这是相当精彩的地方，丝毫不亚于纯文学作品。在《碧血剑》中曾有一幕，写到闯王帐下群雄见到当世第一美人莫不疯狂，甚至袁承志这样的人见到她也是心中荡漾。多年之后，韦小宝第一次见到陈圆圆时虽已韶华不再，但风韵不减当年，仍禁不住"张大了口竟然合不拢来..."；再说，女儿阿珂都把韦小宝震撼得"我要死了"，更别说人家老娘了。

貌美不是好事情，汉族文化的传统思维是红颜祸水，其实"冲冠一怒为红颜"关卿何事? 不过是政治家争权夺势的借口罢了。陈圆圆终其一生，何其不幸也。在吴三桂和李自成这两个枭雄中间注定得不到得不到幸福，更为天下人唾骂，这也是造化使然。金庸小说中的陈圆圆，是不折不扣的悲剧形象，其后半生青灯古佛，心怀天下苍生，那是万分难得的菩萨心肠了。

最后多说一笔，如果陈圆圆不那么美貌的话，恐怕中国历史要改写吧? 当然，这个有点扯远了，否则，该有同学说"丘处机不该路过牛家村"这回事儿了。

--EOF--

金庸小说本来是网友写烂了的题材。这是给公司内刊投稿的文章（美女题材在家里是个禁忌，我这也是冒着被老婆揍的风险)。算是重温了一下渐行渐远的武侠文化吧。

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