|
I just tried the stored procedure using the loop join and it is 100 times faster. I hadn’t heard of that type of join before. Can you recommend a good web site or book where I can get more information on developing databases and stored procedures maximizing performance?
Thanks for your detailed response.
Jason W.
|
|
|
|
|
loop doesn't indicate a different type of join - it causes the underlying query interpreter to use a different logical operator to perform the operation.
It appears that the original query (without the hint) was using a hash-match join: hashing the data selected from one side of the join and comparing to a table of hashes generated from the other side of the join.
Adding the loop hint causes it to use the Nested Loops operator, which is the simplistic way to implement a join: consider each row on the left-hand side in turn, look through the right-hand side to see if anything matches. The loop over the right-hand side is nested inside the loop for the left-hand side; hence, Nested Loops (although SQL Server may decide to swap the tables or indexes over if appropriate).
If there isn't much data on at least one side of the join, nested loops can perform better than hash match. The downside of nested loops is simply that the server must iterate over every row of one side the number of times that there are rows on the other side.
When compiling a stored procedure, SQL Server caches the compiled execution plan. It does this the first time that the procedure is executed. When pressure for memory increases, SQL Server removes any pages that haven't been touched recently from cache - including cached execution plans.
However, when compiling the procedure for the first time, SQL Server is guided by the parameters. If the parameters will be very different, causing greatly different execution paths, the cached execution plan can be terrible. To force a recompile every time, add WITH RECOMPILE before the AS keyword in the definition of the procedure. As always, you should measure the effect this has.
Another reason the query optimizer might pick poor indexes is if your index statistics are not up to date. Generally SQL Server updates statistics automatically, but you might have turned this off. Look up UPDATE STATISTICS and sp_autostats. Alternatively, consider updating statistics via a scheduled maintenance job. The statistics tell SQL Server how selective an index is, and thus how useful it is in finding rows.
If your execution plan indicates that SQL Server is having to join two indexes on one table together - perhaps seeking one and scanning the other - and your query didn't join the table onto itself, you may find that defining a new index that includes all the columns projected or referenced (excluding the primary key columns, if this table has a clustered index) may help. If a single index contains all the data required, the query is referred to as a covered query. SQL Server can handle a covered query simply by reading the index - it never has to read the table, since all data is stored in the index.
I mention excluding the primary key columns if a clustered index. This is because, if a table has a clustered index, SQL Server stores the clustered index data as the 'destination' part of all non-clustered indexes - to find the rest of the row, after reading the non-clustered index, it has to seek through the clustered index. If there isn't a clustered index, it stores the row number instead.
Care should be taken, because inserts, updates and deletes take more time the more indexes are present.
For more information, try http://www.sql-server-performance.com/[^] or Inside SQL Server 2000[^] by Kalen Delaney (MS Press) - also see the book's website[^].
|
|
|
|
|
Thanks for the detailed response. I am still trying to figure out what a hint is, andy’s message made reference to it also, I will look into that. I have taken a quick look through at the http://www.sql-server-performance.com site you recommended it appears to have a great deal of content. Taking a look at a few of the articles there is a lot I need to learn.
Again, I truly appreciate the your help.
Jason W.
|
|
|
|
|
Hint \Hint\, v. i.
To make an indirect reference, suggestion, or allusion; to
allude vaguely to something.(from www.dict.org[^]).
Basically, it's a non-compulsory suggestion to SQL Server's query optimiser about how to perform the query (although locking hints are compulsory). Much like using inline or register in C++ - the compiler may choose to follow your suggestion, but it may ignore you.
|
|
|
|
|
Ok I was getting the impressing that hints was a key word in sql. Correct me if I’m wrong but when you say hints it means using something like ‘with(index=ID_Index)’, in my script. When I uses this type of statement it is telling the compiler that I think it should use this index but the compiler can over ride that if it wants.
Jason W.
|
|
|
|
|
|
This is a bit tangential: an article in August's MSDN Magazine[^] talks about generating an XML file from a SQL Server data schema.
You should then be able to use an XML parser, or XSLT, to translate into the format you want.
|
|
|
|
|
|
I would like to change my app from DAO35 to DAO36 or higher, to support ACCESS2000 DBs. How to convert a existing ACCESS97 database programmatically (using DAO)? Is there anything comparable to the RepairDatabase / CompactDatabase calls ?
Thank you.
|
|
|
|
|
Couldn't you just open each database in Access 2000 and select "convert" when asked to open or convert? How many databases are you talking about?
|
|
|
|
|
the following is the code written to add data into the database!
i get the error saying
COleSafeArray undefined..
i there any need to include any other header files fort this to work.
ADO functions are used in this c++ client!
COleSafeArray vaFieldList;
vaFieldList.CreateOneDim(VT_VARIANT, 4);
// Fill the fields name now
long lArrayIndex[3];
lArrayIndex[0] = 0;
vaFieldList.PutElement( lArrayIndex, &(_variant_t("kEy")) );
lArrayIndex[0] = 1;
vaFieldList.PutElement( lArrayIndex, &(_variant_t("nAme")) );
lArrayIndex[0] = 2;
vaFieldList.PutElement( lArrayIndex, &(_variant_t("tYpe")) );
lArrayIndex[0] = 3;
vaFieldList.PutElement( lArrayIndex, &(_variant_t("vAlue")) );
// Create an array of values to be added
COleSafeArray vaValueArray;
vaValueArray.CreateOneDim(VT_VARIANT, 4);
//Fill the values in each field
lArrayIndex[0] = 0;
vaValueArray.PutElement( lArrayIndex, &(_variant_t("rob")) );
lArrayIndex[0] = 1;
vaValueArray.PutElement( lArrayIndex, &(_variant_t("surya")) );
lArrayIndex[0] = 2;
vaValueArray.PutElement( lArrayIndex, &(_variant_t("kakka")) );
lArrayIndex[0] = 3;
vaValueArray.PutElement( lArrayIndex, &(_variant_t("mac")) );
// call Addnew of recordset now
pRecordset->AddNew( vaFieldList, vaValueArray );
pRecordset->Close();
ranjani
|
|
|
|
|
question about BCP process.
The problem is when I transfer the data in date time type field the date '00000000' is not transferable, which is understandable, however it also kicking out some data with appropriate date. Any idea why it occur?
|
|
|
|
|
I have three tables, a main table and two subtables that are related to the main table by the main tables key field. In my application I set up three OleDbDataAdapters to read three seperate tables into three tables of a dataset and then I add to the datasets relation collection to link the tables together. The problem is that while I can update the main table by calling the update method of it's DataAdapter, I can't do the same with the other two tables. When I call their update method, nothing happens. I get no errors and the rows that where marked to be updated are still marked to be updated (i.e. AcceptChanges hasn't been called). Also, I can't change the key field even in the main table. Changes to the key simply get ignored and don't get written back to the database. Does anybody know what is happening here? I suspect it's something to do with the tables being related.
|
|
|
|
|
Please show your code which updates the Child Tables.
Stefan
|
|
|
|
|
Okay, thanks for your reply. Here's an example of the problem I'm having. I've included some of the code I've added just to try and figure out what's happening. When I iterate throw the rows of the child table I find that all the rows have RowState = Unchanged, even though some of them have an Original and a Proposed value. I believe they are not getting updated because the RowState is Unchanged, but I can't figure out why the RowState is Unchanged when there is clearly a Proposed value available. Surely setting a Proposed value for a row should automatically change the RowState?
<br />
public void UpdateData()<br />
{<br />
connDB.Open();<br />
SubApt.RowUpdating += new OleDbRowUpdatingEventHandler(MyRowUpdateHandler);<br />
<br />
string s = "";<br />
foreach (DataRow thisRow in m_myDS.Tables["tblSub"].Rows)<br />
{<br />
s += thisRow["Key"] + " -> " + thisRow["Field1"] + " " + thisRow.RowState.ToString() + "\n";<br />
if (thisRow.HasVersion(DataRowVersion.Proposed))<br />
{<br />
s += thisRow["Field1", DataRowVersion.Original] + " " + thisRow["Field1", DataRowVersion.Proposed] + "\n";<br />
}<br />
}<br />
MessageBox.Show(s);<br />
<br />
MainApt.Update(m_myDS.Tables["tblMain"]);<br />
SubApt.Update(m_myDS.Tables["tblSub"]);<br />
connDB.Close();<br />
}<br />
|
|
|
|
|
1. Did you call AcceptChanges somewhere? Don't call AcceptChanges before Adap.Update().
2. Clear the EventHandler for RowUpdate. This may call AcceptChanges()
3. Try to edit a Row and immediatly afterwards check it's RowState. If the RowState is unchanged I don't know what's wrong. AcceptChanges is a tricky thing: after this call all Rows are marked unchanged! So there is nothing what could be Updated by the Update Method of Apt.
Please inform me about Point 3.
Stefan
|
|
|
|
|
STW wrote:
1. Did you call AcceptChanges somewhere? Don't call AcceptChanges before Adap.Update().
No, I have not called AcceptChanges explictly anywhere in my program. I had thought that perhaps calling update on the main table might automatically call AcceptChanges on the child table, but not updating the main table didn't fix the problem. I was also thinking that calling AcceptChanges should move the proposed value into the original value shouldn't it? That's not been happening.
STW wrote:
2. Clear the EventHandler for RowUpdate. This may call AcceptChanges()
I tried it without the EventHandler and it makes no difference. I only put the EventHandler there in the hopes of being able to intercept the call and figure out what was happening. As it turns out, the event never gets fired.
STW wrote:
3. Try to edit a Row and immediatly afterwards check it's RowState. If the RowState is unchanged I don't know what's wrong. AcceptChanges is a tricky thing: after this call all Rows are marked unchanged! So there is nothing what could be Updated by the Update Method of Apt.
Okay, I tried manually changing the value of one field in the child table like this:
<br />
m_myDS.Tables["subtable"].Rows[0]["Field1"] = 101;<br />
And if I then iterate through the rows in the table, I can see that row has been changed to RowState.Modified and it doesn't have a proposed value anymore. Further, when I call the update that row does, in fact, get updated in the database.
|
|
|
|
|
Okay, I just figured something out. If, while I'm iterating through the rows, I call EndEdit on each row it will set the RowState to modified (if it has actually been modified). So the problem seem to be that when a datarow is bound to my form, BeginEdit is implicitly called, and when that particular row becomes unbound, it should automatically call EndEdit on that row. But it isn't doing it for my child table. Now, I don't want to have to iterate through all my records and call EndEdit on every one of them before I run my update because I have a lot of records and I expect it to grow rapidly once (if) I finish my app. I'm thinking I could intercept the PositionChanged event of my CurrencyManager, but I think at that point the position has already changed so I won't be able to grab the previous row to call EndEdit on it. I could try and intercept every button or event that results in a change of position and call EndEdit before I change the position, but that's a pain since I'd have to remember to do that in several different places. I'd also have to make sure I call EndEdit on the current row when the Update button is clicked, but that's not a major problem (because it's only one place).
So I think I can work around my problem, but I'd be much happier if I could just figure out why the CurrencyManager isn't calling EndEdit and fix it!
|
|
|
|
|
I am getting an error msg:
"The conversion of char data type to smalldatetime data type resulted in an out-of-range smalldatetime value."
when I have the following code in where close:
and n.dateentered between (case
When DatePart (dw , getdate())=2 Then (getDate()-3 )
When DatePart (dw , getdate())=4 Then (getDate()-2 )
When DatePart (dw , getdate())=6 Then (getDate()-2 )
Else GetDate() End ) and (getdate()-1)
but when I run with this (I put dates manually) it is fine.
and n.dateentered between '09/20/2003' and '09/29/2003'
Any idea why?
|
|
|
|
|
I have tested the SQL query using SQL Server Enterprise Manager and it's working fine for me.
My guess is that n.dateentered is of type "smalldatetime" and GetDate actually returns "datetime" instead.
You might want to try one of the following:
1. Use CAST(x as y) e.g. CAST( (case when...end) AS smalldatetime) ->I've tested this with the code and it works
2. Use DateAdd() function instead of getDate()-3
3. Use DatePart to format your date ranges to yyyymmdd format
|
|
|
|
|
code for adding a new record,deleting a record that already exists and modifying an existing record needed in C++
ranjani
|
|
|
|
|
Is there a way to get the actual SQL commands that the OleDbDataAdapter.Update method is passing? I'm having a problem due to the fact that every time I try and run my Update command, I get an exception thrown by the db (access) claiming that there is a syntax error in my SQL command. Trouble is I can't seem to figure out how to get the actual text of the command (after the adapter has filled in the parameters). I'm pretty confident that the command that I set as the Update command is okay, so I want to see if the problem is with how the adapter has decided to fill in the parameters?
I tried hooking the RowUpdating event, but I still only get the command text without the parameters inserted?
|
|
|
|
|
The Update Command is an OleDBCommand. You can get the property CommandText from it...;)
Free your mind...
|
|
|
|
|
But the CommandText only has the command before the parameters have been filled in. I need the actual command that is sent to the database when I call the Update method of my OleDbDataAdapter. Is there a way to get this?
|
|
|
|
|
Okay, I tracked down the problem by systematically removing fields from my Update statement. The problem is caused by a date field. I have something like this (but with a lot more fields):
<br />
SQLUpdate = "UPDATE myTable SET Field1 = @Field1, Date = @Date, WHERE Key = @Key";<br />
Then I have this:
<br />
OleDbCommand myCmd = new OleDbCommand(SQLUpdate,myConnection);<br />
myCmd.Parameters.Add("@Field1", OleDbType.VarWChar, 20, "Field1");<br />
myCmd.Parameters.Add("@Date", OleDbType.Date, 0, "Date");<br />
<br />
myApt.UpdateCommand = myCmd;<br />
What's the right way to handle the date field in an Access database. Even the command builder seems to fail at this!! BTW, the Date field is bound to a DatePicker control on my form, perhaps something is getting lost in the translation?
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
