We have an AS400 mainframe running our DB2 transactional database. We also have a SQL Server setup that gets loaded nightly with data from the AS400. The SQL Server setup is for reporting.
I can link the two database servers, BUT, there's concern about how big a performance hit DB2 might suffer from queries coming from SQL Server.
Basically, the fear is that if we start hitting DB2 with queries from SQL Server we'll bog down the transactional system and screw up orders and shipping.
Thanks in advance for any knowledge that can be shared.
Anyone who has a pat answer for a performance question is wrong :-) The appropriate answer is always 'it depends.' Performance tuning is best done via measure, change one variable, repeat.
DB2 for i shouldn't even notice if someone executes a 1,000 row SELECT statement. Take Benny's suggestion and run one while the IBM i side watch. If they want a hint, use WRKACTJOB and sort on the Int column. That represents the interactive response time. I'd guess that the query will be complete before they have time to notice that it was active.
If that seems unacceptable to the management, then perhaps offer to test it before or after hours, where it can't possibly impact interactive performance.
As an aside, the RPG guys can create Excel spreadsheets on the fly too. Scott Klement published some RPG wrappers over the Java POI/HSSF classes. Also, Giovanni Perrotti at Easy400.net has some examples of providing an Excel spreadsheet from a web page.
I'd mostly agree with Buck, a 1000 row result set is no big deal...
Unless of course the system is looking through billions of rows across hundreds of tables to get the 1000 rows you are interested in.
Assuming a useful index exists, 1000 rows shouldn't be a big deal. If you have IBM i Access for Windows installed, there's a component of System i Navigator called "Run SQL Scripts" that includes "Visual Explain" that provides a visual explanation of the query execution plan. View that you can ensure that an index is being used.
On key thing, make sure the work is being done on the i. When using a standard linked table MS SQL Server will attempt to pull back all the rows then do it's own "where".
select * from MYLINK.MYIBMI.MYLIB.MYTABE where MYKEYFLD = '00335';
Whereas this format sends the statement to the remote server for processing and just gets back the results:
select * from openquery(MYLINK, 'select * from mylib.mytable where MYKEYFLD = ''00335''');
Alternately, you could ask the i guys to build you a stored procedure that you can call to get back the results you are looking for. Personally, that's my preferred method.
Charles
Related
This question is quite general, however, i can not find a good answer for it.
What are the possibilities for using an external database with MS Access?
I see that MySQL can be used, but I would have to setup a ODBC connection and install drivers on every machine. The issue is that I have a software developed in MS Access that uses a lot of data, and it gets very slow at processing the data when i include a lot of data.
The software analyzes data from wind turbines, so it is used by different customers and it may contain a lot of different turbines with 50,000+ rows in each data set.
I would like these turbine data to be stored in a separate file that is pointed to by MS Access, so I include the software + whatever turbine data wanted.
As it is now, i have a lot of Access database files where the data is included in the software. It becomes impossible to keep track of - Especially when I do an edit to the source code of the software, which is do a lot these days.
Another issue is that the users may only have Access Runtime.
What are my options here? Is the best method to use the Access Link function?
Best regards, Emil.
Edit:
SQL's - Can they be combined? :
SELECT q_DataLimited.YAW001, q_DataLimited.YAW002
FROM q_DataLimited
WHERE (((q_DataLimited.YAW002)>Degree_dsp() And (q_DataLimited.YAW002)<Degree_dsp_high()));
And
SELECT Count(q_WindRose_PCU.YAW001) AS CountOfYAW0011
FROM q_WindRose_PCU;
Edit 2:
Public Degree As Long
Public Function Degree_dsp() As Long
Degree_dsp = Degree * 20
End Function
I have the degree as a counter outside the function in a form being:
For Degree = 0 To 17
DoCmd.OpenQuery "q_WindRose_PCU"
DoCmd.Close
Next Degree
Edit 3:
How to combine a query and the append of it to a table?
SELECT q_PowerBinned.Bin, Avg(q_PowerBinned.POW001) AS AvgOfPOW001, StDev(q_PowerBinned.POW001) AS StDevOfPOW001, Avg(q_PowerBinned.WSP001) AS AvgOfWSP001, StDev(q_PowerBinned.WSP001) AS StDevOfWSP001, Avg(q_PowerBinned.POW002) AS AvgOfPOW002, StDev(q_PowerBinned.POW002) AS StDevOfPOW002, Avg(q_PowerBinned.WSP002) AS AvgOfWSP002, StDev(q_PowerBinned.WSP002) AS StDevOfWSP002, Count(q_PowerBinned.Bin) AS CountOfBin
FROM q_PowerBinned
GROUP BY q_PowerBinned.Bin;
And then the append of the above to a table:
INSERT INTO t_Average_Stored ( Bin, PowAvg001, WindAvg001, PowAvg002, WindAvg002, n_samples, PowDev001, WindDev001, PowDev002, WindDev002 )
SELECT q_Average_Temp.Bin, q_Average_Temp.AvgOfPOW001, q_Average_Temp.AvgOfWSP001, q_Average_Temp.AvgOfPOW002, q_Average_Temp.AvgOfWSP002, q_Average_Temp.CountOfBin, q_Average_Temp.StDevOfPOW001, q_Average_Temp.StDevOfWSP001, q_Average_Temp.StDevOfPOW002, q_Average_Temp.StDevOfWSP002
FROM q_Average_Temp;
I see already a few suggestions in the comments, but I am going to answer the general question you posted. In short, the possibilities are endless.
MS Access, and Excel for that matter, have excellent external data tools that allow you to connect to almost any external data source and leverage on regular SQL-based databases or even use OLAP cubes to do your analysis. Access itself should be powerful enough to handle the data sets you mention. Even Access 2010 should be able to handle millions of records with relative ease.
MS Access does have a significant limitation, which is the 2GB file size. Once your database reaches 2GB, everything goes out the window and you are very likely to get data corruption. This is a well known issue, but I don't think you are anywhere near these limits.
Before considering an upgrade, though, there are a few things to suggest:
Analyze the structure of your data and your database. Perhaps your tables are too big (lots of columns) and unnecessarily redundant. It may make sense to process the raw data you receive to split it into different tables that reduce the redundancy and improve performance.
Look into indexing some key fields in your tables. This is heavily dependent on the type of analysis you do and what queries are most common. Read up on indexes and how to use them and explore some options with actual datasets. You may be surprised how queries that used to take minutes to run become almost instantaneous when the right indexes are created and maintained.
Analyze your queries for performance. If I remember correctly, MS Access 2010 had a performance analyzer, which could improve your queries to make them run more efficiently.
If you have already looked into the items above and you decide you really need to take a step up, one fairly easy path (and inexpensive) is to install SQL Server Express, which you can download for free from Microsoft. Access was made to talk to SQL Server and the performance is many times better. You can run SQL Server Express in your personal pc and use it as a back-end for Access, or you could actually install it in a networked pc and use it as a server (behind a firewall, of course, NEVER connected to the Internet). In this setup you can access your data from several PCs.
One key thing to keep in mind once you start using Access as a front end, is that you want to push the processing to the back end, not keep it in Access. The best way to do this is to create what Access calls pass-through queries. These queries are written in the backend's native SQL language and are sent to the back end server for processing. Only the processed data comes back. If you don't do this, for example by creating the queries in the visual editor in Access instead, the raw data will be sent to Access and then Access will try to create your results. This, as you can imagine, can actually be a lot slower than your initial situation, so don't do it.
If you are not a SQL expert and need a visual editor, there is a tool that you can download from Microsoft: SQL-Server Management Studio Express. The query editor is not that different from Access and will allow you to create queries in a visual manner, but in Transact-SQL (the language of SQL Server). You can also manage your SQL Server Express with this tool and maintain your data in this manner (import, export, etc). You can create the SQL statements you need in this editor and then copy and paste into the pass-through queries in Access. The data will be available for you in the program you are familiar with, but with the power of a much bigger database engine behind the scenes.
Since I do not want to sound like a Microsoft shill, I definitely want to mention other options for external data that could be equally or even more powerful than SQL Server Express. The only reason I mentioned these is because you are already familiar with Microsoft products and the learning curve is a bit less steep. Also, most things should work together out of the box.
The first option that comes to mind is SQLite, which is a high performing database that is actually file-based. It is very small, yet very powerful and fast, and it is ideal for a locally based application like what you mention. There are also lots of graphical interfaces for SQLite and you can connect to it via ODBC from Access. Again, you want to run everything using pass-through queries and let SQLite pick up the load. SQLite is Open Source and it is free.
If you are keen on having "a real database server", then MySQL is probably the next step up. Also Open Source and free, it is very popular, which means lots of places to get support and different graphical interfaces to choose from.
Any search for Open Source Database will give you even more options to try and choose from.
One key thing to keep in mind: if you install any database server in your PC, it will become a server, and will start advertising its services in your local network or on the internet if you bring it to a local Starbucks. Be careful with that, learn how to start/stop the services in your PC, and make sure you turn them off when you are not behind a firewall. There are many exploits for different database servers and you will get quickly detected once your PC starts advertising its newly acquired abilities.
Just to close, there is no difference in the performance of Access and the runtime. Just the ability to edit the queries and so on. Whatever front end you create in Access, your users will be able to utilize in the same manner.
Is there a way to detect which columns and which tables are used in a SQL Server database?
Just against SQL Server 2012 would be fine.
We can assume there are no '*' for column usage in the legacy site.
Details:
I'm working on updating the table structure of a legacy system to work on a newer database (2005 to 2012)
There are a lot of bloated tables, with columns that are never used, and even tables that are never used. Identifying all of them would be a pain by manually going through the code.
(My assumption is that we can run SQL Server profiler while running a complete test pass on the app, but I don't know a convenient way to extract the columns)
Thanks.
You can list dependencies for a table in Mgmt Studio, which will show you which SPs, UDFs etc depend on the table in question. You can't do that for a single field. However, that would only show the internal dependencies. Sql Profiler would theoretically show you all fields that get requested by your app however it still would not really tell you much as the app may not do anything with the values it retrieves. If you are going to change the db it would only really make sense to put in the effort if you were also going to change the app and then you should be really get some input from users on what features are still useful and what is broken before you get too involved in a back-end refresh. IMHO.
Is it possible to build a generic query that verifies and if needed corrects a whole table schema?
Example:
On my dev machine i have a sql server with some tables. I, and others, make changes to the tables and sometimes misses to notify the others about them. :/
I want to build a query that reads the dev sql tables and creates a query that i can run one another sql server and updates that table there so that they are equal.
I cant drop the table and recreate it unfortunately. I dont want to change any of the data.
If this is to hard with sql syntax is there some tools that can do this for me? The sql tables are almost always on different machines and most likely i cant connect directly to them from the same place. So tha fixing/verifying needs to be done "offline".
Time is not of the essence, it can be a very slow query as long as it works.
update: I want to verify the sql schema and not the content of the table
update2: We are using SQL Server 2008 R2
It is possible, but not easy. This kind of tool is called a Data Dictionary, and you can write one yourself (see advice from the Database Programmer) or you can buy a commercial one, for example RedGate's SQL Compare.
Is there any system defined sp is available in SQL Server 2005, to find what are the tables are got affected when the applicaion is running and we are navigating from one page to other.
There's really no easy way (if any at all) to find that out, unfortunately.
As SQL Server MVP Aaron Bertrand puts it in his excellent blog post When was my database / table last accessed? :
A frequently asked question that surfaced again today is, "how do I see when my data has been accessed last?" SQL Server does not track this information for you. SELECT triggers still do not exist. Third party tools are expensive and can incur unexpected overhead. And people continue to be reluctant or unable to constrain table access via stored procedures, which could otherwise perform simple logging. Even in cases where all table access is via stored procedures, it can be quite cumbersome to modify all the stored procedures to perform logging.
However, with the help of the sys.dm_db_index_usage_stats DMV (dynamic management views) function and some clever T-SQL programming by Aaron, you can find out a few of those answers - check out his very enlightening blog post for details !
However: since this information is based on a DMV and the "D" in DMV stands for dynamic, those values are only valid since the last server reboot and will be wiped out and not preserved when you next have to restart your SQL Server process / reboot your server machine.
I know of none, but Profiler offers a solution. Run Profiler (can be a developer box) and navigate. It will create an output file for you of what is being run.
There are also code tools that show dependencies. I would imagine at least one shows dependencies on SQL objects.
I don't think so. You can run the SQL-profiler to see which commands are fired against the SQL server but you will have to parse them yourself.
You could also try to empty the query cache and then look at it when your navigation is done, but this cache will be contaminated by other queries running on the server (including the ones run by SQL server itself).
We have a windows MFC app that is written against an access database on a company server. The db is not that big: 19 MB. There are at most 2-3 users accessing it at any one time. It is used in a factory environment where access speed (or lack thereof) over the intranet becomes noticeable as it is part of the manufacturing time for our widgets.
The scenario is this: as each widget is completed, it gets a record in the db.. by the end of the year, the db is larger and searching for a record takes longer and longer. The solution so far has been to manually move older records to an archival table about once a year.
We are reworking other portions of this app right now, and it would be a good time to move to another db if we are going to do it.
It is my understanding that if we were using sql, the search time would not go up as the table gets bigger because the entire .mdb does not have to be sent over the network each time. Is this correct? Does anyone have any insight about whether it could be worth it to go to the trouble (time and money) of migrating to a new db, or should I just add more functionality to the application we have now, and maybe automatically purge the older records from time to time, and add additional facilities to the app to get at the older records when needed?
Thanks for any wisdom you can share..
Since your database is small and very few users, I could not make a solid case for migration. I would definetly set up an script to archive old records on a more frequent basis (don't archive into same db, this would somewhat defeat the purpose).
But also make sure two things are correct as well.
INDEXES. If your queries start slowing down, make sure you have proper indexes
http://support.microsoft.com/kb/304272
Your network connection between computers is fast. Maybe upgrade to gigabit cards and router? Possibly put the db on a scsi drive (raid 10 for speed and redundancy)
Throwing advanced technology at simple problems is an expensive way to go and not always the answer!
First of all, the information that the whole table and the whole database is transferred across the network is simply incorrect. If the queries are indexed, then the search times should not go up that much over time.
As others have mentioned spending the time + money to setup and maintain and then have someone maintain and manage and support that database server is certainly a possibility here. However, keep in mind that simply migrating a JET based application to sql server in many cases will run slower, and in fact sql server is slower then JET when no network is involved.
So, I would take some time to ascertain why things slow down so much, and also check into how indexing is setup.
So, just keep in mind that it is pure folklore and myth that the whole tables and whole database is transferred over the network. This concept is ONLY DUE to most people really not having any computer training and not knowing and understanding how the JET data engine works.
I would probably move to either Microsoft SQL Server 2008 R2 Express Edition (free) or MySQL (free) if there is both funding and time to put in a data access layer. Because you will be making requests of a remote server and not operating on data at the local workstation this move is very involved from the development standpoint.
However you should analyze whether or not its more cost effective to perform your archival process quarterly or monthly, and just move the archive database to SQL Server 2008 R2 Express Edition. (You can install the Microsoft SQL Server Management Studio client tools on workstations and query the archival database for faster reports on historical data without rewriting your entire production application; similar solutions exist for using MySQL or other OSS/free RDBMS).
I have cilents with 300 mb databases although they should be upsizing to SQL Server for other reasons. 19 Mb is relatively small. If performance is bad enough that archiving speeds things up then check the indexes to the tables for all your sorting and selection fields. Albert gave you a good URL there to check.
Entire MDB files do not go down the wire. Unless you are missing indexes.
Instead of shipping the DB over the network to the client and then performing queries, you could instead write a small wrapper on the server that handles requests, looks up the result in the Access DB (using SQL + the Access ODBC driver), and returns the result. This avoids the overhead of a large migration you might not need and still gets rid of the basic problem the users are experiencing.
Moving to a "proper" database solution is the best long term solution, but if your needs scale linearly and slowly over the next 30 years, it's hard to justify an expensive migration. That said, if you expect to really ramp up, or want to be more "future-proof", migrating now will likely save money/time.
It is my understanding that if we were
using sql, the search time would not
go up as the table gets bigger because
the entire .mdb does not have to be
sent over the network each time. Is
this correct?
This general idea is true for almost all databases. The idea of a database is to separate your application from the actual data. The data resides in a database server. Your application doesn't.
Does anyone have any insight about
whether it could be worth it to go to
the trouble (time and money) of
migrating to a new db
Yes. Having proposed this many times. It's expensive. It's complicated. Your MS-Access database will never get better or faster.
Other database servers will (and can) get faster and more sophisticated. After all, you're not sending .MDB files through a network anymore. The limitations are reduced. You're working with standard SQL through ODBC. Any database will work at the end of ODBC. You can fire vendors to find better, faster, cheaper products. Once you stop using Access you have choices.
Either stop using Access now or plan to suffer with it forever. And remake this decision every year until the end of time.