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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
http://www.rampant-books.com/book_2005_2_rac_ssd_tuning.htm
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