Oracle Database Tips by Donald Burleson
Allocating Oracle Objects into Multiple
RAM Data Buffers
Since very few Oracle databases can afford the
cost of full RAM caching, many rules of thumb have been developed for
the segregation and isolation of cached objects. Some of these rules
of thumb will yield clues about the best way to utilize SSD in a
solid-state Oracle environment:
Tables that experience large-table full-table scans will benefit
from the largest supported block size and should be placed in a
tablespace with the largest block size.
is not being set to the largest
supported block size for the server, the
parameter should not be used. Instead, a
whatever the user's max is, should be created and all tables that
experience frequent large-table full-table scans should be assigned
to the largest buffer cache in the database.
In many cases, Oracle SQL statements
will retrieve index information via an index range scan, scanning
the b-tree or bitmap index for ranges of values that match the SQL
search criteria. Hence, it is beneficial to have as much of an index
residing in RAM as possible. One of the first things the Oracle 9i
DBA should do is to migrate all of their Oracle indexes into a large
blocksize tablespace. Indexes will always favor the largest
For those databases that fetch
small rows randomly from the disk, the Oracle DBA can segregate
these types of tables into 2K tablespaces. While disk is becoming
cheaper every day, it is still not wise to waste any available RAM
by reading in more information to RAM than is actually going be used
by the query. Hence, many Oracle DBAs will use small block size is
in cases of tiny, random access record retrieval.
For those Oracle tables that contain raw, long raw, or in-line LOBs,
moving the table rows to large block size will have an extremely
beneficial effect on disk I/O. Experienced DBAs will check
make sure that the blocksize is larger than the average size. Row
chaining will be reduced while at the same time the entire LOB can
be read within a single disk I/O, thereby avoiding the additional
overhead of having Oracle to go out of read multiple blocks.
When the recycle
pool was first introduced in Oracle8i, the idea was the full-table
scan data blocks, which are not likely to be reread by other
transactions, could be quickly flushed through the Oracle SGA
thereby reserving critical RAM for those data blocks which are
likely to be reread by another transaction. In Oracle9i, the RECYCLE
pool can be configured to use a smaller block size.
The block size for a table's tablespace should always be greater
than the average row length for the table,
Not only is it smaller than the average row length, rows chaining
occurs and excessive disk I/O is incurred.
The TEMP tablespace will benefit from the largest supported
blocksize. This allows disk sorting to happen in large blocks with a
minimum of disk I/O.
These suggestions are very important to the study
of the best way to utilize SSD as an alternative caching mechanism.
However, recent TPC-C benchmarks make it clear
that very large RAM regions are a central component in high
performance Oracle databases. The 2004 UNISYS Oracle Windows
benchmark exceeded 250,000 transactions per minute using a
Windows-based 16-CPU server with 115 gigabytes of Oracle data buffer
cache. The following are the
Oracle parameters that were used in the benchmark, and the benefit of
large scale RAM caching is clear:
At this point, it is very clear that RAM resources
are an important factor in maintaining the performance of I/O
intensive Oracle systems.
code depot for complete scripts
This is an excerpt from the book
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Market Survey of SSD vendors for
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:
||performance metrics and notes
sustained external throughput, 400,000 random IOPS
1,00MB/s write with ×4 PCIe, 3 microseconds latency
Solid Access Technologies
sustained read or write per port (full duplex is 719MB/s), with
8 x 4Gbps FC ports aggregated throughput is approx 2,000MB/s,
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.:
SSD support details.
vs. Flash SSD
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:
Avg. Read speed
Avg. write speed