title: Does a typical ACID RDBMS sync to disk every commit?
body: <p>The 'D' in ACID means "Durability" which is defined by Wikipedia as: "every committed transaction is protected against power loss/crash/errors and cannot be lost by the system and can thus be guaranteed to be completed".</p>
  
  <p>However, this would mean that every transaction must be sync'd to disk before being reported as successful, not just flushed.  ('flush'=sent to the operating system level, 'sync'=sent to the physical disk platter).  This would make it impossible to implement a high transaction rate RDBMS.</p>
  
  <p>Do popular RDBMS's really sync every transaction?</p>