EnterpriseDB Architecture Oracle Tips by Burleson Consulting

The EnterpriseDB architecture is different from Oracle in specifics but is conceptually very similar (Figure 2.35).  The most important component in the EnterpriseDB architecture is the edb-postmaster program.  In the simplest terms, the Postmaster is the server.   

Figure 2.35: EnterpriseDB Architecture

Here is a very quick run down of the processes in figure 2.35.

The Postmaster manages server processes.  The Postmaster is the traffic cop; while directing traffic, it is also controlling and communicating with the user processes.  Several processes that are independent in Oracle are performed by the Postmaster in EnterpriseDB.

Checkpoint & DB Writer:  In EnterpriseDB, the Postmaster has a checkpoint and db writer process very much like Oracle’s CKPT and DBW processes.  These processes make sure your data is written to the file system (in the form of the database data files).  This process is called “writing dirty buffers to disk”.

Recovery:  In EnterpriseDB, the recovery process (which runs in the Postmaster process) performs much the same function as Oracle’s SMON process.  Recovery is responsible for crash recovery in the event EnterpriseDB was not properly shutdown.  

User Session:  In EnterpriseDB, a user process runs under the moniker edb-postgres.exe in MS-Windows or as postgres in Linux.  This is a single user Postmaster process and is an actual client connection.  There is memory associated with the session. 

Shared Memory:  The Shared Memory works much like the SGA of an Oracle instance.  Shared memory is the workspace and contains both the short-term and long-term memory of the EnterpriseDB brain, the Postmaster.  

Buffer Cache:  Almost any disk-based database will have some kind of a buffer cache.  A buffer cache is a memory area that holds recently accessed data blocks (recently used rows of data).  A database will keep the blocks in memory in case the same records need to be accessed again.  Keeping the blocks in memory theoretically helps with performance.

Write Ahead Log:  The Write Ahead Log performs much the same function as Oracle’s Log Writer; it flushes data from an internal log buffer to the REDO log on disk. 

REDO Logs:  The REDO logs in EnterpriseDB serve exactly the same function as the REDO logs in Oracle.  A REDO log holds a copy of every transaction run through the database.  We use the REDO log to recover a database in case we lose a data file or have a hard disk crash. 

Archiving:  In EnterpriseDB, there is no native Archiving process.  The Administrator can configure a third party tool (or even a tool provided by your OS) to archive your log files.  You should archive your log files using some methodology.  You should keep archives for a time span of at least a couple of full system backups.

This is an excerpt from the book "EnterpriseDB: The Definitive Reference" by Rampant TechPress.