pub struct DatabaseFileSizeInPages(/* private fields */);Expand description
§In-header database size (4 Bytes)
The in-header database size is a 4-byte big-endian integer at offset 28 into the header stores the size of the database file in pages. If this in-header datasize size is not valid (see the next paragraph), then the database size is computed by looking at the actual size of the database file. Older versions of Sqlite ignored the in-header database size and used the actual file size exclusively. Newer versions of Sqlite use the in-header database size if it is available but fall back to the actual file size if the in-header database size is not valid.
The in-header database size is only considered to be valid if it is non-zero and if the 4-byte change counter at offset 24 exactly matches the 4-byte version-valid-for number at offset 92. The in-header database size is always valid when the database is only modified using recent versions of Sqlite, versions 3.7.0 (2010-07-21) and later. If a legacy version of Sqlite writes to the database, it will not know to update the in-header database size and so the in-header database size could be incorrect. But legacy versions of Sqlite will also leave the version-valid-for number at offset 92 unchanged so it will not match the change-counter. Hence, invalid in-header database sizes can be detected (and ignored) by observing when the change-counter does not match the version-valid-for number.