了解MySQL的内存使用情况会导致PHP(PDO) [英] Understanding memory usage of MySQL result in PHP (PDO)

问题描述

我试图了解为什么单个PDO结果的内存使用量如此之高.以下是有关查询/结果的几件事:

I am trying to understand why the memory usage for a single PDO result is so high. Here are a few things to know about the query/result:

• 我要从单个表中提取单个VARCHAR(6)列
• 结果少于3万行
• 获取此结果将使用PHP中约12MB的内存(来源:memory_get_usage)
• 如果我将结果json_encode并转储到文件中，则实际数据(以文本形式)仅为〜1MB
• 使用在Ubuntu 14.04上部署的PHP7，MySQL 5.7.

• I am pulling a single VARCHAR(6) column from a single table
• The result is less than 30K rows
• This fetching this result uses ~12MB of memory in PHP (source: memory_get_usage)
• If I json_encode the result and dump it to a file, the actual data (in text form) is only ~1MB
• Using PHP7, MySQL 5.7, deployed on Ubuntu 14.04.

我的问题是，11MB的膨胀到底从何而来?如果文本形式的实际数据只有大约1MB，那么11MB似乎只是为了解析PHP中的数据而产生的大量开销.是否有一个原因?我想念什么吗?

My question is, where exactly does the 11MB of bloat come in? If the actual data in text form is only about 1MB, then 11MB seems like a lot of overhead just to parse the data in PHP. Is there a reason for this? Am I missing something?

为澄清起见，我正在寻找有关膨胀原因的技术解释，而不是该问题的解决方法.

Just to clarify, I am looking for a technical explanation as to why the bloat exists, not a workaround for the issue.

推荐答案

好，所以感谢Ollie Jones的回答，我意识到我一直在找错地方来获取我的信息.这不是PDO内存使用问题，而是PHP存储其数组的方式问题. (也许问题不是正确的词，而是它的意思)

Ok, so thanks to Ollie Jones's answer, I realized I've been looking in the wrong place for my information. This isn't a PDO memory usage issue but an issue with the way PHP stores its arrays. (Maybe issue isnt the right word, it is what it is)

经过一番挖掘，我发现了这篇非常有用的文章，对PHP如何为数组元素分配内存进行了详尽的介绍:

After a bit of digging I found this incredibly helpful article which gives a great breakdown of how PHP allocates memory for array elements:

https: //nikic.github.io/2011/12/12/How-big-are-PHP-arrays-really-Hint-BIG.html

剧透警报，它为每个元素使用一吨的内存.显然，它在PHP7中变得更好了.文章指出，对于一个简单的整数数组(在PHP5中)，它将使用的内存比整数本身的大小大18倍.由于我看到关联字符串数据增加了12倍，因此id表示，与PHP5相比确实是一个巨大的改进.

Spoiler alert, it uses a TON of memory for each element. Apparently it has gotten a lot better in PHP7. The article states that for a simple integer array (in PHP5) element it will use about 18 times the more memory than the size of the integer itself. Since i'm seeing about a 12* increase on associative string data, id say that is indeed a vast improvement over PHP5.

根据该文章，正在为以下内容分配内存:

According to the article, memory is being allocated for the following:

• zvalue_value联合，与PHP允许的弱类型转换有关
• 类型存储和垃圾收集数据
• Zend内存管理器分配
• 哈希表存储桶

• zvalue_value union, which relates to the weak typecasting that PHP allows
• Type storage and garbage collection data
• The Zend Memory Manager allocation
• Hash table buckets

如果您对此也有兴趣，我强烈建议您阅读该文章，它是一种快速阅读的书，并且有很多有用的信息.

If you had some interest in this as well, I highly recommend reading that article, its a quick read and has a lot of great information.

再次感谢Ollie Jones向我指出正确的方向.

Thanks again to Ollie Jones for pointing me in the right direction.

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