How Oracle Works on Exadata - Oracle Exadata Recipes: A Problem-Solution Approach - page 65

Figure 3-3. I/O processing on Exadata

Here's how it works:

• Oracle foreground or background processes issue database I/O calls, just as they do in non-

Exadata environments.

PARSE/EXEC/FETCH logic on Exadata as they do on non-
Exadata. As blocks are requested, Oracle will check for copies of the blocks in both the local
and all-remote database block buffer caches and perform a logical I/O or block-shipped
logical I/O to satisfy the request. In other words, logical I/O on Exadata is the same as logical
I/O on non-Exadata.

• Oracle processes follow the same

• If a physical I/O is required:

1. On Exadata, the server process constructs an iDB message containing the list of

extents to fetch. Additionally, various pieces of metadata are encapsulated in the
messages that provide further details about the I/O request.

2. On non-Exadata Oracle environments, the database server is responsible for issuing

disk I/O calls.

• iDB = Intelligent Database Protocol. iDB is an InfiniBand-aware network protocol designed by
Oracle, implemented on Reliable Datagram Sockets V3.

sendmsg system calls. These messages are
sent to each of the storage cells in the storage grid, independently.

• iDB messages are transmitted over InfiniBand using

cellsrv processes.
• cellsrv examines the contents and metadata inside the iDB message and makes I/O
processing decisions based on the contents.

• The messages are processed (in other words, received) by storage server