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  Oracle Tips by Burleson

Use of SSD With RAC

Where does SSD technology fit into the RAC environment? Of course if allowed, replacement of the entire disk subsystem would provide the maximum amount of performance gain, but what if the entire disk setup cannot be replaced?

With a RAC environment, the largest performance boost will come with placing the files with blocks that are either most read from disk, or are most passed across the interconnect, on SSD arrays.

For example, the results of block transfer across an interconnect will look like the following:

Segments by CR Blocks Received                                                            CR
       Tablespace                  Subobject  Obj.       Blocks
Owner  Name       Object Name      Name       Type      Received %Total
------ ---------- ---------------- ---------- ----- ------------ ------TPCC   USERS      C_ORDER                     TABLE       36,613  40.59
TPCC   USERS      C_STOCK                     TABLE       17,938  19.89
TPCC   USERS      C_ORDER_LINE_I1             INDEX       10,485  11.62
TPCC   USERS      C_DISTRICT                  TABLE        6,834   7.58
TPCC   USERS      C_NEW_ORDER_I1              INDEX        6,256   6.94

Segments by Current Blocks Received                                                         Current
       Tablespace                  Subobject  Obj.       Blocks
Owner  Name       Object Name      Name       Type      Received %Total
------ ---------- ---------------- ---------- ----- ------------ ------TPCC   USERS      C_ORDER                     TABLE      181,196  77.75
TPCC   USERS      C_STOCK                     TABLE       15,017   6.44
TPCC   USERS      C_NEW_ORDER_I1              INDEX        7,149   3.07
TPCC   USERS      C_DISTRICT                  TABLE        6,781   2.91
TPCC   USERS      C_ORDER_LINE_I1             INDEX        4,446   1.91

In this example, the c_order, c_district and c_stock tables and the c_order_line_i1 and c_new_order_i1 indexes are the best candidates to be moved to SSD, assuming memory modifications are done to ensure they are read from disk.

Oracle Corporation states that index blocks are the most frequently shipped blocks across an interconnect. By placing the indexes in a specialized different block size area of the db buffer cachesand then sizing that to hold a minimal amount of blocks, the index blocks can be forced to be read from an SSD drive. The TPC-C tests in Chapter 4 show that for RAC on SSD, forcing the system to read the blocks rather than transferring them through the interconnect, is the best performance methodology.

The above book excerpt is from:

Oracle RAC & Tuning with Solid State Disk

Expert Secrets for High Performance Clustered Grid Computing

ISBN 0-9761573-5-7

Donald K. Burleson & Mike Ault


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