Drupal Field Value Index and Performance

When we talk about the performance of Drupal, the first thing come to my mind is caching. But today I found another way to make Drupal run a little bit faster. It is not a profound thing, but something may be ignored by many. In work, I need process 56916 records constantly with automated Cron process. It took 13 minutes 30 seconds to process all those records. Adding a new database field index, I reduced the processing time to one minute 33 seconds only. It is more than eight times faster.

Here is the detail. I have about fifty thousand of record that updated daily. Each record I had a hash created and stored in a field. Whenever inserting or updating a record, and I would check and see if this hash code existed in the database. The project requires searching on the field revision table. Here is the code in my custom module.

$exist = db_query("SELECT EXISTS(Select entity_id from {field_revision_field_version_hash} where field_version_hash_value = :hash)", array(':hash' => $hash))->fetchField();
// Return when we had imported the schedule item before.
if ($exist) {
  return;
}

So, checking the hash code in the database became one of the heavy operations. It consumed a lot of system resource. By adding a single query to the field revision table make the process eight times faster. Here is the code I put in the module install file.

// Add version-hash indexes.
if (!db_index_exists('field_revision_field_version_hash', 'version_hash')) {
  db_add_index('field_revision_field_version_hash', 'version_hash', array('field_version_hash_value'));
}

When we build a Drupal website, we are not dealing with database directly. Even though Drupal creates the tables for us, we can still alter the table and make it better.