MySQL: What is a page?

I can't for the life of me remember what a page is, in the context of a MySQL database. When I see something like 8KB/page, does that mean 8KB per row or ...?

 Answers

Database pages are the internal basic structure to organize the data in the database files. Here some informations about the InnoDB model.

From 13.2.11.2. File Space Management:

The data files that you define in the configuration file form the InnoDB tablespace. The files are logically concatenated to form the tablespace. [...] The tablespace consists of database pages with a default size of 16KB. The pages are grouped into extents of size 1MB (64 consecutive pages). The “files” inside a tablespace are called segments in InnoDB.

And from 13.2.14. Restrictions on InnoDB Tables

The default database page size in InnoDB is 16KB. By recompiling the code, you can set it to values ranging from 8KB to 64KB.

Further, to put rows in relation to pages:

The maximum row length, except for variable-length columns (VARBINARY, VARCHAR, BLOB and TEXT), is slightly less than half of a database page. That is, the maximum row length is about 8000 bytes. LONGBLOB and LONGTEXT columns must be less than 4GB, and the total row length, including BLOB and TEXT columns, must be less than 4GB.

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It's the size of which data is stored/read/written to disk and in memory.

Different page sizes might work better or worse for different work loads/data sets; i.e. sometimes you might want more rows per page, or less rows per page. Having said that, the default page size is fine for the majority of applications.

Note that "pages" aren't unique for MySQL. It's an aspect of a parameter for all databases.