Exporting Structure and Data (Backup) - Mastering phpMyAdmin 3.4 for Effective MySQL Management - page 124

A system administrator installing phpMyAdmin for a number of users could choose
to set all these parameters to FALSE , so as to avoid the potential overhead incurred
by a lot of users compressing their exports at the same time. This situation usually
causes more overhead than if all the users were transmitting their uncompressed
files at the same time.
In older phpMyAdmin versions, the compression file was built in the web server
memory. Some problems caused by this were:
• File generation depended on the memory limits assigned to running
PHP scripts.
• During the time the ile was generated and compressed, no transmission
occurred. Hence, users were inclined to think that the operation was not
working and that something had crashed.
• Compression of large databases was impossible to achieve.
The $cfg['CompressOnFly'] parameter (set to TRUE by default) was added to
generate (for GZIP AND BZIP2 formats) a compressed file containing more headers.
Now, the transmission starts almost immediately. The file is sent in smaller chunks
so that the whole process consumes much less memory. The downside of this is a
slightly larger resulting file.
Export formats
We shall now discuss the formats (and the options available once they have been
chosen) that can be selected with the Format sub-panel.
Even if we can export into many formats, only some of these
formats can be imported back using phpMyAdmin.
SQL
The SQL format is useful, as it creates standard SQL commands that would work on
any SQL server.
If the Display comments checkbox is selected, comments are included in the export
file. The first part of the export comprises comments (starting with the -- characters)
that detail the utility (and version) that created the file, the date, and other
environment information. We then see the CREATE and INSERT queries for each table.
phpMyAdmin generates ANSI-compatible comments in the export file. These
comments start with -- . They help with importing the file back on other ANSI SQL-
compatible systems.