I want to how to do following general step:
where to find slow SQL
how to debug SQL (including functions)
how to create index properly
when using "update statistics", when should I use HIGH or LOW, and why?
I am going to write a paper about this topic; any help is welcomed.
One place to start is, funnily enough, the Informix Performance Tuning Guide, one section of the Informix 11.70 Information Centre. In particular, it explains most of what you need to know about UPDATE STATISTICS, and also about automatic update statistics.
For question 3, at one level, there isn't much to it - you follow the syntax from the manuals and it works. I'm guessing though that you're more concerned with whether you should create an index on a table; this would in part follow on from questions 1 and 2.
There are a variety of ways to find slow SQL. If you have OAT (OpenAdmin Tool), then it has ways to report the slowest queries. Alternatively, you can look to SET EXPLAIN.
If you have Informix 11.70, then there is a built-in SPL (stored procedure language) debugging facility. For earlier versions, Server Studio and Sentinel has some support. You can also look at the built-in TRACE facility and the related SET DEBUG FILE statement, but they tend to be tricky to interpret, and don't really give you performance information (more a question of correct vs incorrect functioning).
Related
I have a realy strange problem.
I'm using Oracle 11g.
There is a query executed by Business Objects tool, which the optimizer generate different plans for different users.
When my customer run the BO report it's realy slowly, but when I run it, it's fast.
According to the fact that there is a great plan (take seconds), I tried to enforced the optimizer to use that plan.
The problem is that it's not work.
I tried with baseline and sqlsets but the query used bind variables with different values each time, so it not realy help when the query change.
Is there a way to disable a plan for all sql executions?
This is 1 bad plan.. but can come with a lot of queries becasue of the bind variables.
More, I found in the net information about optimizer_secure_view_merging
parameter that could cause such problem.. but I have few users that got the good plan , not only the owner.. Is that still can be that ?
source:
https://oracledb.wordpress.com/2007/04/10/execution-plans-differents-with-different-users/
If there is another idea what to do..
I'd not call this problem a realy strange.
There is a lot of possible causes that diferent user get different behaviour for the same query.
On trivial cause is to query a non-qualified table.
select * from TAB
This query will access different tables for different users.
The next possibility are different Optimizer Initiation Parameters that could cause that the optimizer for one user may use features that are prohibited for other user.
I'd recommend as a simplest way for troubelshooting to perform the Oracle 10053 trace for both queries.
The trace file contains the complete list of the used paramaters and a simple diff could provide a usefull hint.
If the parameters are not the cause, you'll see in the trace the details why different access paths in the execution plan was taken. (A good introduction to understand 10053 trace is the paper of Wolfgang Breitling I linked above).
What is the best considered way to save and use Views, SPs and UDFs for SSRS reporting services that will be used by many users and some reports subscribed being sent out?
Do I:
Write it to a table overnight via scheduled jobs to do a direct read to the pre-saved query results?
Use a SP with temp tables with indexes based on each Views SQL to have it all in one place for the SSRS?
If the answer is that 'it depends on what I want', I would be grateful if you point me to any resources that can give me an idea of ideal setup to get query data to SSRS with minimal performance issues.
Thanking you kindly
Background/Explanation
SQL Server is not foreign to me but I don’t consider myself experienced (1 year) enough in developing 'etiquette' when it comes to crafting the parts of SQL Server. I feel I'm developing a lot of bad habits formed from using basic SQL knowledge, online searches and the odd MS SQL server course. The amount of searching done has been endless and I’m not saying there isn’t an answer out there for each part of SQL Server (UDFs, SPs and Views) out there.
The company I work for has many servers, many databases, for many outsourced front end systems being used. The issue is performance and the more I search the more I realize the setup of our databases could now maybe completely negligent and amateur. When I joined the setup used a lot of views each 'end' view had a dependency tree of over 4+ views including use of functions, each view ranging from aggregate calculations for Statistics to rearranging via pivots and unpivots. The reason given to me was so that we can pick out the parts that have gone wrong in which view. To no surprise the server has now suddenly had enough of this and peaks at 100% every time a report or view ran affecting the front end systems performance for the users.
My PP stresses my frustration and my position with the company (code monkey) in finding an answer myself which has resulted in pushing the keys back in the keyboard with opposable thumbs and appeal to the experts here.
This question is really too broad for stackoverflow. I'll try to give you a quick overview of what I think you're asking but really you're asking for way too much for a single answer here. This site is mainly focused around solving a specific problem and not the general process of development. I expect someone will probably come along and close your question.
Nightly table loads
Depending on the complexity of the task this is exactly what SSIS (SQL Server Integration Services) is for. You can build automated processes that do data transformations and data loads. It is used to build maintainable data integration solutions. Learning to use SSIS (especially properly) is a whole task though. In fact the 3rd exam for the SQL Server 2012 MCSA is exclusively about SSIS. Though if your table loads are not that complicated running them as SQL Tasks could be just as effective.
Database structure and use of views/SPs/functions/etc
This is an incredibly deep subject and it is totally dependent on what you're trying to do, how your data is structured, what kind of hardware you've got running, etc. Certainly using views, functions, and stored procedures can be good. They enable code re-use and allow you to encapsulate the logic for SSRS reports away from the actual report writers.
However, the SQL needs to be well written or it will suffer from performance problems. But, of course, that is just how it is no matter where you put the code. Even if the SQL is just a dataset in an SSRS report it will run slowly and hammer the server if it isn't written well. If the database isn't configured correctly it can have terrible performance. Indexes and other techniques for speeding up databases will always be important.
Above all everything needs to be documented so that someone else (or your later self) can make sense of it in ten months when something breaks.
Training
I would highly recommend trying to convince your employer to send you on some courses to learn SQL Server if they expect you to be developing complex database solutions. Certainly taking the courses to get your MCSA in SQL Server 2012 would be very useful. Getting the certification certainly opened my eyes to many possibilities for achieving things that I didn't know about before or just hadn't thought of.
The first exam will cover writing SQL queries and the different things that can help performance and the many cool features that you can leverage when retrieving or writing data. The second exam will cover database server administration, troubleshooting, and some performance tuning. The third exam is all about SSIS and how to warehouse your data to enable better analysis and reporting.
Even if you just read the Microsoft Learning books for these exams and never take the tests you will gain a lot of knowledge. There are other books that are good too such as T-SQL Fundamentals by Itzik Ben-Gan but ultimately it sounds like you need to get a lot deeper knowledge of the SQL Server platform before you can really make good design decisions about how to implement your solutions.
Conclusion
In the end, programming is programming. Trying to make a maintainable solution that works is your first goal. Tuning the performance of the system comes after that. The specifics of the languages and platforms don't take away from any of that. But in order to get the best performance out of a system you need knowledge about that system. An answer on here isn't going to be able to give you everything you need to know.
I have a SQL query:
ANALYSE TABLE CUST_STAT COMPUTE STATISTICS;
it works well in Oracle, but recently I am switching to use PostgreSQL, I change the SQL to:
ANALYSE CUST_STAT COMPUTE STATISTICS;
I already read the manual section on partitioning, I know the TABLE keywords is not needed in PostgreSQL, but I still getting error for the PARTITION :
ANALYZE CUST_STAT PARTITION CUST_STAT_P201307 ;
Can anyone help?
There is no COMPUTE STATISTICS sub-command for ANALYZE in PostgreSQL.
ANALYZE tablename;
per the manual on ANALYZE.
There is also no PARTITION keyword. PostgreSQL's partitioning is limited and largely manual. See the user manual section on partitioning.
The PostgreSQL manual is quite detailed and pretty good. I suggest reading it rather than trying to apply Oracle experience directly to Pg. They're not the same DB.
On partitioning, this tutorial is a bit old and is targeted at EnterpriseDB, but I think it uses only standard features, and it might help introduce the concepts. I haven't reviewed it in detail.
Another simple step-by-step example is on this blog entry.
Examples are no substitute for understanding though, and this is an area you need to understand, not just follow recipes for. If you don't have time for that I strongly recommend seeking someone who does to help you with your implementation in-depth.
I'm working on a very large query, in a inherited application. This is a large insert-query, that takes 4 tables with well over a million records. I know, I would also rather have this in SQL-server, but there is no infrastructure at this customer to do this :-)
This query has worked for over a year. However, the source-tables keep on growing, and last week it threw the dreaded 'out of system resources'-error. Bummer...!
I think it is possible to optimize this query. Working in MySQL, I would use the explain-command, to see where optimalisation might occur. Is there a equivalent of this in Access? I cannot seem to find it....
kind regards,
Paul
Probably Jet ShowPlan is closest to what you want. You will have to set a registry key. Then query plan information gets dumped to a text file named SHOWPLAN.OUT. You can read about the details in this article on TechRepublic: Use Microsoft Jet's ShowPlan to write more efficient queries
Also try the Performance Analyzer wizard. You can ask it to examine your query alone, or also ask it to examine table or other queries used by that query.
If you haven't compacted the database recently, see whether that improves performance. Compacting also updates index statistics which allows the engine to make better decisions for the query plan.
When you write rather complex SQL for Oracle, sooner or later you will have to apply the odd execution hint because Oracle can't seem to figure out the "best" execution plan itself.
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/hintsref.htm
Now this is certainly not a SQL standard. But still, I'm wondering, are there any other RDBMS that support these kinds of hints, and I really mean hints that are "embedded" in SQL? Are they similar, syntactically (i.e. also placed between the SELECTkeyword and the first selected COLUMN)? Do you know of a general documentation page comparing hints in various RDBMS?
N.B: I'm mostly interested in these RDBMS: Postgres, MySQL, HSQLDB, H2, Derby, SQLite, DB2, Sybase, SQL Server
I know that in db2 the plans are made fixed in some way, not how. In Oracle 11g there are other options besides adding hints to queries. These are SQLProfiles and SQLPlan Baselines, both very powerful. I just finished a performance tuning project where we did not add even a single hint to the code, on the contrary.
You can add Oprimizer Hints to any SQL Server Query
The PLAN clause allows you to define a particular plan to your query in Firebird.
AFAIK, nothing standard nor close to it, but in general, you can do this in a lot of RDBM's, but not all.
I'd also remind you, if you are making some sort of comparison with other DB platforms, that hints in Oracle are entirely non-binding. Which is to say that Oracle is free to disregard your hint if it so chooses.
Hints can be helpfull but I find that I rarely use them anymore - at least not compared to the past when I was working with the older optimizers in earlier Oracle versions. Back then hints were much more of a staple to performance tuning than they are now.