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feha


Posts: 712
Posted: 05/21/2006, 2:59 AM

googling i found this:

Quote :
Avoid making SELECT * calls, instead explicitly name all the columns you want to retrieve, and if you are using MySQL, test your queries using the EXPLAIN statement. To optimize loops, consider using duplicated code instead of low iteration loops; also use as many static values, such as count($array) values, inside the loop as you can, generating their values before the loop once.
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marcwolf


Posts: 361
Posted: 05/30/2006, 11:54 PM

Depending on your database you can REALLY speed things up using memory tables.

We use MySQL and have a fairly large code lookup table. On some display we cah hit this tabel 10 times or more. its often the only way to achieve normalisation on very large records.

We noted that the system was getting slower regardless of howmany indexes and optimisations we used.

In the end we made a duplicat of the code table and assigned it the type of HEAP.

Now - as the code table is updaed in only one place we just tell MySQl to do a replace from the real table into the HEAP one is there are any changes.

Speed increase was fantastic

With a little bit of work the above can be applied to any grouping of small code value tables like Country, State, etc that takes a lot of hits.

Take Care

Dave
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mamboBROWN


Posts: 1712
Posted: 05/31/2006, 7:49 AM

Upgrading MySQL
Also, keep in mind that upgrading MySQL to 5.x version also will give you some features that could aid in speeding up your applications. Such as views and stored procedures.

If that's not an option checkout possible configuration changes or purchase the MySQL book that gives you pointers and hints on improving speed and response time of your MySQL database(s).
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Andres Rormoser
Posted: 06/27/2006, 6:11 AM

SQL Server Speed UP Tips


1. Normalize your tables
There are two common excuses for not normalizing databases: performance and
pure laziness. You'll pay for the second one sooner or later; and, about
performance, don't optimize what's not slow. And, more frequent than the
inverse, the resulting design is slower. DBMS's were designed to be used
with normalized databases and SQL Server is no exception, so design with
normalization in mind.

2. Avoid using cursors

Use cursors wisely. Cursors are fundamentally evil. They force the database
engine to repeatedly fetch rows, negotiate blocking, manage locks, and
transmit results. They consume network bandwidth as the results are
transmitted back to the client, where they consume RAM, disk space, and
screen real estate. Consider the resources consumed by each cursor you build
and multiply this demand by the number of simultaneous users. Smaller is
better. And good DBAs, most of the time, know what they are doing. But, if
you are reading this, you are not a DBA, right?

Having said this the other question that comes is, If I were to use cursors
then .... ? Well here are my 20Cents on cursor usage. Use the appropriate
cursors for the job in hand.

Don't use scrollable cursors unless required

Use readonly cursors if you donot intend to update. This would be
90% of the situations.

Try to use Forward Only cursor when using cursors

Don't forget to close and deallocate the cursors used.

Try to reduce the number of columns and records fetched in a
cursor

3. Index Columns

Create Index on columns that are going to be highly selective. Indexes are
vital to efficient data access; however, there is a cost associated with
creating and maintaining an index structure. For every insert, update and
delete, each index must be updated. In a data warehouse, this is acceptable,
but in a transactional database, you should weigh the cost of maintaining an
index on tables that incur heavy changes. The bottom line is to use
effective indexes judiciously. On analytical databases, use as many indexes
as necessary to read the data quickly and efficiently.

Now a classic example is DONOT index an column like "Gender". This would
have a selectivity of 50% and if your table is having 10 Million records,
you can be least assured that using this index you may have to travel half
the number of rows ... Hence maintaining such indexes can slow your
performance.

4. Use transactions

Use transaction judiciously. This will save you when things get wrong.
Working with data for some time you'll soon discover some unexpected
situation which will make your stored procured crash. See that the
transaction starts as late as possible and ends as early as possible. This
would reduce the requirement to lock down the resources while accessing. In
short,

5. Analyze deadlocks

Access your tables on the same order always. When working with stored
procedures and transactions, you may find this soon. Any SQL programmer /
database analyst would have come across this problem. If the order changes
then there wold be a cyclic wait for resources to be released and the users
would experience a permanent hang in the application. Deadlocks can be
tricky to find if the lock sequence is not carefully designed. To summarize,
Deadlock occurs when two users have locks on separate objects and each user
is trying to lock the other user's objects. SQL Server automatically detects
and breaks the deadlock. The terminated transaction will be automatically
rolled back and an error code 1205 will be issued.

6. GOTO Usage

Avoid using the infamous GOTO. This is a time-proven means of adding
disorder to program flow. There are some cases where intelligent use of GOTO
is preferable to dogmatically refusing to use it. On the other hand,
unintelligent use of GOTO is a quick ticket to unreadable code.

7. Increase timeouts

When querying a database, the default timeout is often low, like 30 seconds.
Remember that report queries may run longer than this, specially when your
database grows. Hence increase this value to an acceptable value.

8. Avoid NULLable columns

When possible, normalize your table and separate your nullable columns. They
consume an extra byte on each NULLable column in each row and have more
overhead associated when querying data. It will be more flexible and faster,
and will reduce the NULLable columns. I'm not saying that NULLs are the evil
incarnation. I believe they can simplify coding when "missing data" is part
of your business rules.

9. TEXT datatype

Unless you are using it for really large data. The TEXT datatype is not
flexible to query, is slow and wastes a lot of space if used incorrectly.
Sometimes a VARCHAR will handle your data better. You can also look at the
"text in row" feature with the table options for SQL Server 2000. But still
I would stick to the first statement, Avoid using them on first place.

10. SELECT * Usage

Its very difficult to get out of this habit, but believe me this is very
essential. Please DONOT use this syntax. Always qualify the full list of
columns. Using all columns increases network traffic, requires more buffers
and processing, and could prove error prone if the table or view definition
changes.

11. Temporary tables usage

Unless strictly necessary. More often than not a subquery can substitute a
temporary table. In SQL Server 2000, there are alternatives like the TABLE
variable datatype which can provide in-memory solutions for small tables
inside stored procedures too. If I were to recollect some of the advantages
of using the same:

A table variable behaves like a local variable. It has a
well-defined scope, which is the function, stored procedure, or batch in
which it is declared. Within its scope, a table variable may be used like a
regular table.

However, table may not be used in the following statements: INSERT
INTO table_variable EXEC stored_procedure SELECT select_list INTO
table_variable statements.

Table variables are cleaned up automatically at the end of the
function, stored procedure, or batch in which they are defined.

Table variables used in stored procedures result in fewer
recompilations of the stored procedures than their counterparts temporary
tables.

Transactions involving table variables last only for the duration
of an update on the table variable. Thus, table variables require less
locking and logging resources

12. Using UDF

UDF can replace stored procedures. But be careful in their usage. Sometimes
UDFs can take a toll on your applications performance. And UDFs have to
prefixed with the owners name. This is not a drawback but a requirement. I
support usage of SPs more than UDFs.

13. Multiple User Scenario

Sometimes two users will edit the same record at the same time. While
writing back, the last writer wins and some of the updates will be lost.
It's easy to detect this situation: create a timestamp column and check it
before you write. Code for these practical situations and test your
application for these scenarios.

14. Use SCOPE_IDENTITY

Dont do SELECT max(ID) from MasterTable when inserting in a Details table.
This is a common mistake, and will fail when concurrent users are inserting
data at the same instance. Use one of SCOPE_IDENTITY or IDENT_CURRENT. My
choice would be SCOPE_IDENTITY as this would give you the identity value
from the current context in prespective.

15. Analyze Query Plans

The SQL Server query analyzer is a powerful tool. And surely is your friend,
and you'll learn a lot of how it works and how the query and index design
can affect performance through it. Understand the execution plan that the
execution plan window shows for potential bottlenecks.

16. Parameterized queries

Parameterize all your queries using the sp_executesql. This would help the
optimzer to chace the execution plans and use the same when requested teh
second time. You can cache-in the time required to parse, compile and place
the execution plan. Avoid using of D-SQL as much as possible.

17. Keep Procedures Small

Keep SPs small in size and scope. Two users invoking the same stored
procedure simultaneously will cause the procedure to create two query plans
in cache. It is much more efficient to have a stored procedure call other
ones then to have one large procedure.

18. Bulk INSERT

Use DTS or the BCP utility and you'll have both a flexible and fast
solution. Try avoiding use of Insert statement for the Buld loading feature,
they are not efficent and are not designed for the same.

19. Using JOINS

Make sure that there are n-1 join criteria if there are n tables.

Make sure that ALL tables included in the statement are joined. Make sure
that only tables that

Have columns in the select clause

Have columns referenced in the where clause

Allow two unrelated tables to be joined together are included.

20. Trap Errors

Make sure that the @@ERROR global variable is checked after every statement
which causes an update to the database (INSERT, UPDATE, DELETE). Make sure
that rollbacks (if appropriate) are performed prior to inserting rows into
an exception table

21. Small Result Set

Retrieving needlessly large result sets (for example, thousands of rows) for
browsing on the client adds CPU and network I/O load, makes the application
less capable of remote use, and limits multi-user scalability. It is better
to design the application to prompt the user for sufficient input so queries
are submitted that generates modest result sets.

22. Negative Arguments

Minimize the use of not equal operations, <> or !=. SQL Server has to scan a
table or index to find all values to see if they are not equal to the value
given in the expression. Try rephrasing the expression using ranges:

WHERE KeyColumn < 'TestValue' AND KeyColumn > 'TestValue'

23. Date Assumption

Prevent issues with the interpretation of centuries in dates, do not specify
years using two digits. Assuming dates formats is the first place to break
an application. Hence avoid making this assumption.

24. SP_ Name

DONOT start the name of a stored procedure with SP_. This is because all the
system related stored procedures follow this convention. Hence a valid
procedure today may clash with the naming convention of a system procedure
that gets bundled with a Service pack / Security patch tomorrow. Hence do
not follow this convention.

25. Apply the latest Security Packs / Service Packs

Even though this point applies to the network and the database
administrators, it is always better to keep up-to date on the software's.
With the "slammer" virus and many more still outside, it is one of the best
practices to be up-to date on the same. Consider this strongly.

26. Using Count(*)

The only 100 percent accurate way to check the number of rows in a table is
to use a COUNT(*) operation. The statement might consume significant
resources if your tables are very big because scanning a large table or
index can consume a lot of I/O. Avoid these type of queries to the maximum.
Use short circuting methods as EXISTS etc. Here is one other way you can
find the total number of rows in a table. SQL Server Books Online (BOL)
documents the structure of sysindexes; the value of sysindexes.indid will
always be 0 for a table and 1 for a clustered index. If a table doesn't have
a clustered index, its entry in sysindexes will always have an indid value
of 0. If a table does have a clustered index, its entry in sysindexes will
always have an indid value of 1.

SELECT object_name(id) ,rowcnt
FROM sysindexes
WHERE indid IN (1,0) AND OBJECTPROPERTY(id, 'IsUserTable') = 1

27. Ownership Chaining

Try using this feature (available from SQL Server 2000 SP3), for permission
management within a single database. Avoid using this feature to manage
permissions across database.

28. SQL Injection

Security has been a prime concern for everyone. Hence validate all the
incoming parameters at all levels of the application. Limit the scope of
possible damage by permitting only minimally privileged accounts to send
user input to the server. Adding to it, run SQL Server itself with the least
necessary privileges.

29. Fill-factor

The 'fill factor' option specifies how full SQL Server will make each index
page. When there is no free space to insert new row on the index page, SQL
Server will create new index page and transfer some rows from the previous
page to the new one. This operation is called page splits. You can reduce
the number of page splits by setting the appropriate fill factor option to
reserve free space on each index page. The fill factor is a value from 1
through 100 that specifies the percentage of the index page to be left
empty. The default value for fill factor is 0. It is treated similarly to a
fill factor value of 100, the difference in that SQL Server leaves some
space within the upper level of the index tree for FILLFACTOR = 0. The fill
factor percentage is used only at the time the index is created. If the
table contains read-only data (or data that very rarely changed), you can
set the 'fill factor' option to 100. When the table's data modified very
often, you can decrease the 'fill factor' option to 70 percent, for example.
Having explained page splits in detail I would warn you in over looking at
this point because more free space means that SQL Server has to traverse
through more pages to get the same amount of data. Hence try to strike a
balance and arrive at an appropriate value.

30. Start-up Procedures

Verify all the stored procedures for safety reasons.

31. Analyze Blocking

More often than not any implementers nightmare would be to see a blocking
process. Blocking occurs when a process must wait for another process to
complete. The process must wait because the resources it needs are
exclusively used by another process. A blocked process will resume operation
after the resources are released by the other process. Sometimes this can
become cyclic and the system comes to a stand still. The only solution is to
analyze your indexing strategy and table design. Consider these points
strongly.

32. Avoid Un-necessary Indexes

Avoid creating un-necessary indexes on table thinking they would improve
your performance. Understand that creating Indexes and maintaining them are
overheads that you incur. And these surely do reduce the throughput for the
whole application. You can create a simple test on a large table and find it
for yourself how multiple indexes on the same column decrease performance.


33. Consider Indexed Views

Sometimes we would require an view to be indexed. This feature is bundled
with SQL Server 2000. The result set of the indexed view is persist in the
database and indexed for fast access. Because indexed views depend on base
tables, you should create indexed views with SCHEMABINDING option to prevent
the table or column modification that would invalidate the view. Hence using
them can reduce a lot of load on the base tables but increases the
maintainability.


34. WITH SORT_IN_TEMPDB Option

Consider using this option when you create an index and when tempdb is on a
different set of disks than the user database. This is more of a tuning
recommendation. Using this option can reduce the time it takes to create an
index, but increases the amount of disk space used to create an index. Time
is precious, disk is cheaper.


35. Reduce Number of Columns

Try to reduce the number of columns in a table. The fewer the number of
columns in a table, the less space the table will use, since more rows will
fit on a single data page, and less I/O overhead will be required to access
the table's data. This should be considered strongly by applications that
talk across different machines. More the unwanted data passed more is the
network latency observed.


"feha" <feha@forum.codecharge> wrote in message
news:2544703a178839c@news.codecharge.com...
> googling i found this:
>
>
Quote :
> Avoid making SELECT * calls, instead explicitly name all the columns you
> want
> to retrieve, and if you are using MySQL, test your queries using the
> EXPLAIN
> statement. To optimize loops, consider using duplicated code instead of
> low
> iteration loops; also use as many static values, such as count($array)
> values,
> inside the loop as you can, generating their values before the loop once.
>
> :-)
> _________________
> Regards
> feha
> Vision.To Design
> www.vision.to
> wowdev.com
> ---------------------------------------
> Sent from YesSoftware forum
> http://forums.codecharge.com/
>

feha


Posts: 712
Posted: 06/27/2006, 7:09 AM

Hello Andreas
Thank you for these great tips. :-)
_________________
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feha

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