Log queries:
You could collect all the queries during core/plugin/theme upgrades to see what happens. Just follow these two steps:
1) You should add:
define( 'SAVEQUERIES', TRUE );
to your wp-config.php file to collect all queries during a page load into the $wpdb->queries array. Just remember to remove it afterwards.
2) Then you could log it into the sql.log file. Here's a simple example:
/**
* Dump all database queries to the /wp-content/sql.log file.
*/
add_action( 'shutdown', function(){
$file = WP_CONTENT_DIR . '/sql.log'; // Edit this filepath to your needs.
if( current_user_can( 'manage_options' )
&& file_exists( $file )
&& is_writeable( $file )
&& isset( $GLOBALS['wpdb']->queries )
)
file_put_contents(
$file,
date( 'c' ) . PHP_EOL . print_r( $GLOBALS['wpdb']->queries, TRUE ),
FILE_APPEND
);
});
or use the query filter of the wpdb class to log only the INSERT, UPDATE and DELETE queries:
/**
* Log the INSERT, UPDATE, DELETE database queries to the /wp-content/sql.log file.
*/
add_filter( 'query', function( $query ){
if( FALSE !== stripos( $query, 'UPDATE ' )
|| FALSE !== stripos( $query, 'INSERT ' )
|| FALSE !== stripos( $query, 'DELETE ' )
) {
$file = WP_CONTENT_DIR . '/sql.log'; // Edit this filepath to your needs.
if( file_exists( $file ) && is_writeable( $file ) )
file_put_contents(
$file,
date( 'c' ) . ' - ' . $query . PHP_EOL,
FILE_APPEND | LOCK_EX
);
}
return $query;
}, PHP_INT_MAX );
Core upgrade files:
For core upgrades these files might be of interest to you
- /wp-includes/version.php
- /wp-admin/includes/upgrade.php
- /wp-admin/includes/schema.php
In the file /wp-admin/includes/upgrade.php you can find the upgrade function: wp_upgrade() that calls the upgrade_all() function. It contains database upgrades for each version in terms of functions like upgrade_xxx()
For example:
...truncated...
if ( $wp_current_db_version < 22422 )
upgrade_350();
if ( $wp_current_db_version < 25824 )
upgrade_370();
if ( $wp_current_db_version < 26148 )
upgrade_372();
if ( $wp_current_db_version < 26691 )
upgrade_380();
maybe_disable_link_manager();
maybe_disable_automattic_widgets();
update_option( 'db_version', $wp_db_version );
update_option( 'db_upgraded', true );
I hope this helps.