英语单词 engine是什么意思
发布网友
发布时间：2022-04-21 23:07
共2个回答
懂视网
时间：2022-04-16 00:00
JSON
MySQL 5.6 has added support for EXPLAIN FORMAT=JSON. The basic use case for that feature is that one can look at the JSON output and see more details about the query plan. More advanced/specific use cases are difficult, though. The problem is, you can’t predict what EXPLAIN FORMAT=JSON will produce. There is no documentation or any kind of convention regarding the contents of JSON document that you will get.
To make sure I’m not missing something, I looked at MySQL Workbench. MySQL Workbench has a feature called Visual Explain. If you want to use, prepare to seeing this a lot:
In Workbench 6.1.4 you get it for (almost?) any query with subquery. In Workbench 6.1.6 (released last week), some subqueries work, but it’s still easy to hit aquerywhose EXPLAIN JSON output confuses workbench.
Looking at the source code, this seems to be just the start of it. The code in MySQL Server is not explicitly concerned with having output of EXPLAIN FORMAT=JSON conform to any convention. Workbench also has a rather ad-hoc “parser” that walks over JSON tree and has certain arbitrary expectations about what nodes should be in various parts of the JSON document. When these two meet, bugs are a certainty. I suspect the real fun will start after a few releases of the Server (fixing stuff and adding new features) and Workbench (trying to catch up with new server while supporting old ones).
My personal interest in all this is that we want tosupport EXPLAIN JSON in MariaDB. MariaDB optimizer hasextra features, so we will have to extend EXPLAIN JSON. I was looking for a way to do it in a compatible way. However, current state of EXPLAIN JSON in MySQL doesn’t give one a chance.
Posted inEXPLAIN,mysql,mariadbon May 23rd, 2014 by spetrunia| |
热心网友
时间：2022-04-15 21:08
engine 英[ˈendʒɪn] 美[ˈɛndʒɪn]
n. 发动机，引擎; 工具; 火车头; 机车;
vt. 给…安装发动机;
[例句]He got into the driving seat and started the engine.
他坐上了驾驶员的位置发动了引擎。
[其他] 第三人称单数：engines 复数：engines 现在分词：engining过去式：engined 过去分词：engined 形近词： ergine
