Why are there so few websites that use http if modified since header fields?

Is

http if modified since used only for static pages? -sharp-sharp-sharp problem description


1. The last update time of the file can only be obtained in seconds. If you modify it several times in a second, you may not be able to get the latest
2. The change in the last update time of the file does not mean that the file content is updated
3. If you need browser caching, you'd better use etag

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b35d7e-2bfbd.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b35d7e-2bfbd.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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