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Oracle Database Tips by Donald Burleson |
The History of Oracle RAM data buffering
When Oracle was first introduced in the early 1990's, RAM was very
expensive and few databases could afford to run large data buffer
regions. Because RAM was such a limited resource, Oracle utilized a
least frequently used algorithm within the data buffer to ensure
that only the most frequently referenced data remained in the data
buffer cache.
As of Oracle10g, seven separate RAM data buffers are available to
hold incoming data blocks. These RAM areas define RAM space for
incoming data blocks and are governed by the following Oracle10g
parameters. The sum of all of these parameter values determines the
total space reserved for Oracle data blocks.
- db_cache_size
- db_keep_cache_size
- db_recycle_cache_size
- db_2k_cache_size
- db_4k_cache_size
- db_8k_cache_size
- db_16k_cache_size
- db_32k_cache_size
This relationship can be expressed mathematically as:
RAM Buffer Size = n/Physical reads
Where n = an observed constant
This relationship is the basis of the Automatic Memory Management (AMM)
features of Oracle10g. Because the Automatic Workload Repository
(AWR) is polling the efficiency of the data buffer, the AMM
component can compute the point of diminishing marginal returns and
reassign SGA RAM resources to ensure optimal sizing for all seven of
the Oracle10g data buffers. In Calculus, the point of diminishing
marginal returns is the second derivative of the equation.
Oracle uses this data to dynamically adjust each of the seven data
buffers to keep them at their optimal size. In AMM, Oracle 10g uses
the AWR to collect historical buffer utilization information and
stores the buffer advisory information in the
dba_hist_db_cache_advice view and offers a host of dba_hist views
for Oracle RAM management.
Market Survey of SSD vendors for
Oracle:
There are many vendors who offer rack-mount solid-state disk that
work with Oracle databases, and the competitive market ensures that
product offerings will continuously improve while prices fall.
SearchStorage notes that SSD is will soon replace platter disks and that
hundreds of SSD vendors may enter the market:
"The number of vendors in this category could rise to several
hundred in the next 3 years as enterprise users become more familiar
with the benefits of this type of storage."
As of January 2015, many of the major hardware vendors (including Sun and
EMC) are replacing slow disks with RAM-based disks, and
Sun announced that all
of their large servers will offer SSD.
Here are the major SSD vendors for Oracle databases
(vendors are listed alphabetically):
2008 rack mount SSD Performance Statistics
SearchStorage has done a comprehensive survey of rack mount SSD
vendors, and lists these SSD rack mount vendors, with this showing the
fastest rack-mount SSD devices:
| manufacturer |
model |
technology |
interface |
performance metrics and notes |
|
IBM |
RamSan-400 |
RAM SSD |
Fibre
Channel
InfiniBand
|
3,000MB/s random
sustained external throughput, 400,000 random IOPS |
|
Violin Memory |
Violin 1010 |
RAM SSD
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PCIe
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1,400MB/s read,
1,00MB/s write with ×4 PCIe, 3 microseconds latency |
|
Solid Access Technologies |
USSD 200FC |
RAM SSD |
Fibre Channel
SAS
SCSI
|
391MB/s random
sustained read or write per port (full duplex is 719MB/s), with
8 x 4Gbps FC ports aggregated throughput is approx 2,000MB/s,
320,000 IOPS |
|
Curtis |
HyperXCLR R1000 |
RAM SSD |
Fibre Channel
|
197MB/s sustained
R/W transfer rate, 35,000 IOPS |
Choosing the right SSD for Oracle
When evaluating SSD for Oracle databases you need
to consider performance (throughput and response time), reliability (Mean Time Between failures) and
TCO (total cost of ownership). Most SSD vendors will provide a
test RAM disk array for benchmark testing so that you can choose the
vendor who offers the best price/performance ratio.
Burleson Consulting does not partner with any SSD vendors and we
provide independent advice in this constantly-changing market. BC
was one of the earliest adopters of SSD for Oracle and we have been
deploying SSD on Oracle database since 2005 and we have experienced SSD
experts to help any Oracle shop evaluate whether SSD
is right for your application. BC experts can also help you choose
the SSD that is best for your database. Just
call 800-766-1884 or e-mail.:
 for
SSD support details. DRAM SSD
vs. Flash SSD
With all
the talk about the Oracle “flash cache”, it is important to note that there
are two types of SSD, and only DRAM SSD is suitable for Oracle database
storage. The flash type SSD suffers from serious shortcomings, namely
a degradation of access speed over time. At first, Flash SSD is 5
times faster than a platter disk, but after some usage the average read time
becomes far slower than a hard drive. For Oracle, only rack-mounted
DRAM SSD is acceptable for good performance:
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Avg. Read speed
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Avg. write speed
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Platter disk
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10.0 ms.
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7.0 ms.
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DRAM SSD
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0.4 ms.
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0.4 ms.
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Flash SSD
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1.7 ms.
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94.5 ms.
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The above book excerpt is from:
Oracle RAC
& Grid Tuning with Solid State Disk
Expert Secrets for High Performance Clustered Grid Computing
ISBN:
0-9761573-5-7
Mike Ault, Donald K. Burleson
http://www.rampant-books.com/book_2005_2_rac_ssd_tuning.htm |
