这个大的怎么样?：

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; YPC 3.2.0; SearchSystem6829992239; SearchSystem9616306563; SearchSystem6017393645; SearchSystem5219240075; SearchSystem2768350104; SearchSystem6919669052; SearchSystem1986739074; SearchSystem1555480186; SearchSystem3376893470; SearchSystem9530642569; SearchSystem4877790286; SearchSystem8104932799; SearchSystem2313134663; SearchSystem1545325372; SearchSystem7742471461; SearchSystem9092363703; SearchSystem6992236221; SearchSystem3507700306; SearchSystem1129983453; SearchSystem1077927937; SearchSystem2297142691; SearchSystem7813572891; SearchSystem5668754497; SearchSystem6220295595; SearchSystem4157940963; SearchSystem7656671655; SearchSystem2865656762; SearchSystem6520604676; SearchSystem4960161466; .NET CLR 1.1.4322; .NET CLR 2.0.50727; Hotbar 10.2.232.0; SearchSystem9616306563; SearchSystem6017393645; SearchSystem5219240075; SearchSystem2768350104; SearchSystem6919669052; SearchSystem1986739074; SearchSystem1555480186; SearchSystem3376893470; SearchSystem9530642569; SearchSystem4877790286; SearchSystem8104932799; SearchSystem2313134663; SearchSystem1545325372; SearchSystem7742471461; SearchSystem9092363703; SearchSystem6992236221; SearchSystem3507700306; SearchSystem1129983453; SearchSystem1077927937; SearchSystem2297142691; SearchSystem7813572891; SearchSystem5668754497; SearchSystem6220295595; SearchSystem4157940963; SearchSystem7656671655; SearchSystem2865656762; SearchSystem6520604676; SearchSystem4960161466; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

这个大的怎么样?：

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; YPC 3.2.0; SearchSystem6829992239; SearchSystem9616306563; SearchSystem6017393645; SearchSystem5219240075; SearchSystem2768350104; SearchSystem6919669052; SearchSystem1986739074; SearchSystem1555480186; SearchSystem3376893470; SearchSystem9530642569; SearchSystem4877790286; SearchSystem8104932799; SearchSystem2313134663; SearchSystem1545325372; SearchSystem7742471461; SearchSystem9092363703; SearchSystem6992236221; SearchSystem3507700306; SearchSystem1129983453; SearchSystem1077927937; SearchSystem2297142691; SearchSystem7813572891; SearchSystem5668754497; SearchSystem6220295595; SearchSystem4157940963; SearchSystem7656671655; SearchSystem2865656762; SearchSystem6520604676; SearchSystem4960161466; .NET CLR 1.1.4322; .NET CLR 2.0.50727; Hotbar 10.2.232.0; SearchSystem9616306563; SearchSystem6017393645; SearchSystem5219240075; SearchSystem2768350104; SearchSystem6919669052; SearchSystem1986739074; SearchSystem1555480186; SearchSystem3376893470; SearchSystem9530642569; SearchSystem4877790286; SearchSystem8104932799; SearchSystem2313134663; SearchSystem1545325372; SearchSystem7742471461; SearchSystem9092363703; SearchSystem6992236221; SearchSystem3507700306; SearchSystem1129983453; SearchSystem1077927937; SearchSystem2297142691; SearchSystem7813572891; SearchSystem5668754497; SearchSystem6220295595; SearchSystem4157940963; SearchSystem7656671655; SearchSystem2865656762; SearchSystem6520604676; SearchSystem4960161466; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

这个是257

Mozilla / 4.0 (compatible;MSIE 8.0;Windows NT 5.1;三叉戟/ 4.0;GTB6; .net CLR 1.1.4322;.net CLR 2.0.50727;.net CLR 3.0.04506.30; InfoPath.2;.net CLR 3.0.04506.648;OfficeLiveConnector.1.3; OfficeLivePatch.0.0;.net CLR 3.0.4506.2152;.net CLR 3.5.30729

这并不是一个用户代理可以达到多大的指示，因为有很多答案显示了他们遇到的边缘情况，但在http://www.useragentstring.com/pages/useragentstring.php?name=All上可以找到的最长的是250字节。

Mozilla / 4.0 (compatible;MSIE 8.0;Windows NT 6.1;三叉戟/ 4.0;SLCC2;.net CLR 2.0.50727;.net CLR 3.5.30729;.net CLR 3.0.30729;Media Center PC 6.0;媒体中心PC 5.0;SLCC1;OfficeLiveConnector.1.5;OfficeLivePatch.1.3;.NET4.0C;Lunascape 6.3。

我会给你一个标准答案:

取你能想到的最大的值，翻倍，这就是答案。

假设用户代理字符串的长度没有限制，并准备存储这样一个值。正如你所看到的，长度是不可预测的。

在Postgres中，有一种文本类型可以接受无限长度的字符串。使用它。

但最有可能的是，您必须在某个时刻开始截断。在一个相当有用的增量(200,1k, 4k)上称它为好，然后扔掉其余的。