We have a 4 column data grid display on a page. I would like to perform a query based on each of the values within each cell of the grid i.e. 4 queries for each row.
This is so I can populate the cell with count of records in db that matches that value.
When each row gets populated by jqgrid, it fires off an ajax call for each cell.
I think it's a very bad idea since I have already discovered the browser limits the number of ajax calls to the same server.
Are there similar limits for ado.net?
I would like to batch these queries together so I do fewer calls to the db, is this what you would do?
How would you approach this?
You could combine your AJAX calls into one, the resulting object contains an array, or multiple properties for each result set, and then you run your SQL in parallel on the server.
Check out this QA for how to use options on how to use TPL and SQL.
Parallel.Foreach SQL querying sometimes results in Connection
me would suggest you to select the associated id data in the first request and populate the values in the UI.
You could either use join or left join in your first query based on your requirement and architecture and fetch the specific column value/ count(id) ( Here you mentioned as the count of records ).
Related
Problem summary:
C# (MVC), entity framework 5.0 and Oracle.
I have a couple of million rows in a view which joins two tables.
I need to populate dropdownlists with filter-posibilities.
The options in these dropdownlists should reflect the actual contents
of the view for that column, distinct.
I want to update the dropdownlists whenever you select something, so
that the new options reflect the filtered content, preventing you
from choosing something that would give 0 results.
Its slow.
Question: whats the right way of getting these dropdownlists populated?
Now for more detail.
-- Goal of the page --
The user is presented with some dropownlists that filter the data in a grid below. The grid represents a view (see "Database") where the results are filtered.
Each dropdownlist represents a filter for a column of the view. Once something is selected, the rest of the page updates. The other dropdownlists now contain the posible values for their corresponding columns that complies to the filter that was just applied in the first dropdownlist.
Once the user has selected a couple of filters, he/she presses the search button and the grid below the dropdownlists updates.
-- Database --
I have a view that selects almost all columns from two tables, nothing fancy there. Like this:
SELECT tbl1.blabla, tbl2.blabla etc etc
FROM table1 tbl1, table2 tbl2
WHERE bsl.bvz_id = bvz.id AND bsl.einddatum IS NULL;
There is a total of 22 columns. 13 VARCHARS (mostly small, 1 - 20, one of em has a size of 2000!), 6 DATES and 3 NUMBERS (one of them size 38 and one of them 15,2).
There are a couple of indexes on the tables, among which the relevant ID's for the WHERE clause.
Important thing to know: I cannot change the database. Maybe set an index here and there, but nothing major.
-- Entity Framework --
I created a Database first EDMX in my solution and also mapped the view. There are also classes for both tables, but I need data from both of them, so I don't know if I need them. The problem by selecting things from either table would be that you can't apply half of the filtering, but maybe there are smart way's I didn't think of yet.
-- View --
My view is strongly bound to a viewModel. In there I have a IEnumerable for each dropdownlist. The getter for these gets its data from a single IEnumerable called NameOfViewObjects. Like this:
public string SelectedColumn1{ get; set; }
private IEnumerable<SelectListItem> column1Options;
public IEnumerable<SelectListItem> Column1Options
{
get
{
if (column1Options == null)
{
column1Options= NameOfViewObjects.Select(item => item.Column1).Distinct()
.Select(item => new SelectListItem
{
Value = item,
Text = item,
Selected = item.Equals(SelectedColumn1, StringComparison.InvariantCultureIgnoreCase)
});
}
return column1Options;
}
}
The two solutions I've tried are:
- 1 -
Selecting all columns in a linq query I need for the dropdownlists (the 2000 varchar is not one of them and there are only 2 date columns), do a distinct on them and put the results into a Hashset. Then I set NameOfViewObjects to point towards this hashset. I have to wait for about 2 minutes for that to complete, but after that, populating the dropdownlists is almost instant (maybe a second for each of them).
model.Beslissingen = new HashSet<NameOfViewObject>(dbBes.NameOfViewObject
.DistinctBy(item => new
{
item.VarcharColumn1,
item.DateColumn1,
item.DateColumn2,
item.VarcharColumn2,
item.VarcharColumn3,
item.VarcharColumn4,
item.VarcharColumn5,
item.VarcharColumn6,
item.VarcharColumn7,
item.VarcharColumn8
}
)
);
The big problem here is that the object NameOfViewObject is probably quite large, and even though using distinct here, resulting in less than 100.000 results, it still uses over 500mb of memory for it. This is unacceptable, because there will be a lot of users using this screen (a lot would be... 10 max, 5 average simultaniously).
- 2 -
The other solution is to use the same linq query and point NameOfViewObjects towards the IQueryable it produces. This means that every time the view wants to bind a dropdownlist to a IEnumerable, it will fire a query that will find the distinct values for that column in a table with millions of rows where most likely the column it's getting the values from is not indexed. This takes around 1 minute for each dropdownlist (I have 10), so that takes ages.
Don't forget: I need to update the dropdownlists every time one of them has it's selection changed.
-- Question --
So I'm probably going at this the wrong way, or maybe one of these solutions should be combined with indexing all of the columns I use, maybe I should use another way to store the data in memory, so it's only a little, but there must be someone out there who has done this before and figured out something smart. Can you please tell me what would be the best way to handle a situation like this?
Acceptable performance:
having to wait for a while (2 minutes) while the page loads, but
everything is fast after that.
having to wait for a couple of seconds every time a dropdownlist
changes
the page does not use more than 500mb of memory
Of course you should have indexes on all columns and combinations in WHERE clauses. No index means table scan and O(N) query times. Those cannot scale under any circumstance.
You do not need millions of entries in a drop down. You need to be smarter about filtering the database down to manageable numbers of entries.
I'd take a page from Google. Their type ahead helps narrow down the entire Internet graph into groups of 25 or 50 per page, with the most likely at the top. Maybe you could manage that, too.
Perhaps a better answer is something like a search engine. If you were a Java developer you might try Lucene/SOLR and indexing. I don't know what the .NET equivalent is.
First point you need to check is your DB, make sure you have to right indexes and entity relations in place,
next if you want to dynamical build your filter options then you need to run the query with the existing filters to obtain what the next filter can be. there are several ways to do this,
firstly you can query the data and extract the values from the return, this has a huge load time and wastes time returning data you don't want (unless you are live updating the results with the filter and dont have paging, in which case you might aswell just get all the data and use linqToObjects to filter)
a second option is to have a parallel queries for each filter that returns the possible filters, so filter A = all possible values of A from data, filter b = all possible values of B when filtered by A in the data, C = all possible values of C when filtered by A & B in the data, etc. this is better than the first but not by much
another option is the use aggregates to speed things up, ie you have a parallel query as above but instead of returning the data you return how many records are returned, aggregate functions are always quicker so this will cut your load time dramatically but you are still repeatedly querying a huge dataset to it wont be exactly nippy.
you can tweak this further using exist to just return a 0 or 1.
in this case you would look at a table with all possible filters and then remove the ones with no values from the parallel query
the next option will be the fastest by a mile is to cache the filters in the DB, with a separate table
then you can query that and say from Cache, where filter = ABC select D, the problem with this maintaining the cache, which you would have to do in the DB as part of the save functions, trigggers etc.
Another solution that can be added in addition to the previous suggestions is to use the /*+ result_cache */ hint, if your version of Oracle supports it (Oracle version 11g or later). If the output of the query is small enough for a drop-down list, then when a user enters criteria that matches the same criteria another user used, the results are returned in a few milliseconds instead of a few seconds or minutes. Result cache is wonderful for queries that return a small set of rows out of millions.
select /*+ result_cache */ item_desc from some_table where item_id ...
The result cache is automatically flushed when any insert/updates/deletes occur on the database tables.
I've done something 'kind of' similar in the past - if you can add a table to the database then I'd explore introducing a 'scratchpad' type table where results are temporarily stored as the user refines their search. Since multiple users could be working simultaneously the table would have to have an additional column for identifying the user.
I'd think you'd see some performance benefit since all processing is kept server-side and your app would simply be pulling data from this table. Since you're adding this table you would also have total control over it.
Essentially I'd imagine the program flow would go something like:
User selects some filters and clicks 'Search'.
Server populates scratchpad table with results from that search.
App populates results grid from scratchpad table.
User further refines search and clicks 'Search'.
Server removes/adds rows to scratchpad table as necessary.
App populates results grid from scratchpad table.
And so on.
Rather than having all the users results in one 'scratchpad' table you could possibly explore having temporary 'scratchpad' tables per user.
I'm developing an ASP.NET app that analyzes Excel files uploaded by user. The files contain various data about customers (one row = one customer), the key field is CustomerCode. Basically the data comes in form of DataTable object.
At some point I need to get information about the specified customers from SQL and compare it to what user uploaded. I'm doing it the following way:
Make a comma-separated list of customers from CustomerCode column: 'Customer1','Customer2',...'CustomerN'.
Pass this string to SQL query IN (...) clause and execute it.
This was working okay until I ran into The query processor ran out of internal resources and could not produce a query plan exception when trying to pass ~40000 items inside IN (...) clause.
The trivial ways seems to:
Replace IN (...) with = 'SomeCustomerCode' in query template.
Execute this query 40000 times for each CustomerCode.
Do DataTable.Merge 40000 times.
Is there any better way to work this problem around?
Note: I can't do IN (SELECT CustomerCode FROM ... WHERE SomeConditions) because the data comes from Excel files and thus cannot be queried from DB.
"Table valued parameters" would be worth investigating, which let you pass in (usually via a DataTable on the C# side) multiple rows - the downside is that you need to formally declare and name the data shape on the SQL server first.
Alternatively, though: you could use SqlBulkCopy to throw the rows into a staging table, and then just JOIN to that table. If you have parallel callers, you will need some kind of session identifier on the row to distinguish between concurrent uses (and: don't forget to remove your session's data afterwards).
You shouldn't process too many records at once, because of errors as you mentioned, and it is such a big batch that it takes too much time to run and you can't do anything in parallel. You shouldn't process only 1 record at a time either, because then the overhead of the SQL server communication will be too big. Choose something in the middle, process eg. 10000 records at a time. You can even parallelize the processing, you can start running the SQL for the next 10000 in the background while you are processing the previous 10000 batch.
I really need an expert's help to answer my query.
Here is the scenario:
Im using an sql select query to retrieve a million records.
I need to perform sorting and grouping on the resultant records which im storing in a datatable( in one execution)
and looping through it for grouping and sorting it.
I know this is so childish and not the right way to process it.
How can i manage the million records effectively and apply the grouping and sorting to it?
Really need help out here. Heard of executing the select query batch wise but how to implement the grouping and sorting while we dont have the entire data in hand?
I cannot go for sql order by and group by directly and that's against my requirement.
Here is what i'm doing right now:
I have the following objects, i.e the column names for grouping and Sorting
List<Group> groupList;
List<Sort> sortList;
DataTable reportData; // Here im having the entire records from db
Im looping through the 'reportData' row by row and matches the current and previous row for the custom grouping and sorting. Would like to know how the same can be done when we are using a batchwise execution or any alternative solution is there?
I need to perform sorting and grouping on the resultant records which
im storing in a datatable( in one execution) and looping through it
for grouping and sorting it.
What for?
Seriously.
Do not pull then try plaing smart with a stupid object model behind (and datasets are not particularly smart, sorry).
Group and sort in your select statement, pull the data lready grouped and joined and be done with it.
A million records was a small amount of data for sql server when the original version was release (4.2 it was, a port of sysase sql server) 17 years of so ago. These days it is something that fits likely into the processor thiird level cache and is nothing a proper sql server even realizes it has just processed.
SQL is particulaly good ad doing projects and ever since they indoruced MARS you can even run multiple queries over one connection, which comes in handy here.
So, go back - throw away the dataset and "I try to program a sort algo" and create proper SQL statements to pull the data as you need it.
Sounds like you should implement Partition Pruning. Partitioning will allow for a separation of content like you are requesting in order to have faster queries.
If I understood correctly, in your case, I would create a temporary database table with the structure I want especially to cover my grouping.
Then I would select the records from main tables and insert them to the temporary one appying all modifications including grouping.
A specific index on how you want them sorted should be also applied.
After that, just select from this table, do what you have to do, and finally if the data are not needed any more, delete the temporary table.
I would choose the above solution because a million of records in memory smells trouble to me...
For example:
1. Lets assume that you would like to group them by their DocumentTypeID
var groupByType = reportData.GroupBy(g=>g.DocumentTypeID);
2. Sorting Alphabetically
var sortAlphabetically = reportData.OrderBy(g=>g.DocumentName);
3. Grouping and Sorting
var groupAndSort = reportData.GroupBy(g=>g.DocumentTypeID)
.OrderBy(g=>g.DocumentName);
4. Sort and Group
var groupAndSort = reportData.OrderBy(g=>g.DocumentName)
.GroupBy(g=>g.DocumentTypeID);
5. Multiple Grouping and sorting
var multipleGroupAndSort = reportData.GroupBy(g=>g.DocumentTypeID)
.GroupBy(g=>g.CreatedOnDate.Month)
.OrderBy(g=>g.DocumentName);
so on and so forth...
But I would still discourage bringing million rows to application. It will cost memory. There are of course ways to manage it through stored procedures etc.
I am working on a site in which as user logs in (first database request) the stored procedure varify password and user id and then returns user record that I put in session to use next.
After this I do a second db request. it returns addresses of user which I put in cache.
Can you pleas guide me is there some way that I can get both sets of data (user record and his address from 2nd table) in one database requests.
plz guide me on this, I am using DAAB (enter prise library) for data access.
Thanks
Modify your SP which has multiple select statements, as in you case is 2. Two select statements in one SP will return two record sets. Verify in SQL Management Studio, when you run your SP, it should show you multiple Grid in bottom panel.
Once your SP is done, call SP from C# code and load result in DataSet. Dataset will have two table, and you can get the data from different table
You can write two select queries in a stored procedure or
Execute two queries one after another . In single query you can execute and receive the data in DataSet .
ExecuteDataset()
So two tables will be returned inside the dataset . You can get the values like
dataset.tables(0)
dataset.tables(1)
Thanks
You would gain nothing from retrieving two results sets in one go, But the code will become more incoherent. Why do you thing you need to merge two logically separate operations into one? Instead of using such questionable methods you can use join to get one result set that contains all the data in one go, but still that seems wrong. I can not see a clean way of doing what you are asking for and any benefits that might be gained.
I have the following code snippet:
var matchingAuthors = from authors in DB.AuthorTable
where m_authors.Keys.Contains(authors.AuthorId)
select authors;
foreach (AuthorTableEntry author in matchingAuthors)
{
....
}
where m_authors is a Dictionary containing the "Author" entries, and DB.AuthorTable is a SQL table. When the size of m_authors goes beyond a certain value (somewhere around the 3000 entries mark), I get an exception:
System.Data.SqlClient.SqlException: The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect.
Too many parameters were provided in this RPC request. The maximum is 2100.
Is there any way I can get around this and work with a larger size dictionary? Alternatively, is there a better way to get all rows in a SQL table where a particular column value for that row matches one of the dictionary entries?
LINQ to SQL uses a parametrized IN statement to perform a local Contains():
...
WHERE AuthorId IN (#p0, #p1, #p2, ...)
...
So the error you're seeing is that SQL ran out of parameters to use for your keys. I can think of two options:
Select the whole table and filter using LINQ to Objects.
Generating an expression tree from your keys: see Option 2 here.
Another option is to consider how you populate m_authors and whether you can include that in the query as a query element itself so it turns into a server-side join/subselect.
Depending on your requirements, you could break apart the work into multiple smaller chunks (first thousand, second thousand, etc.) This runs certain risks if your data is read-write and changes frequently, but it might give you a bit better scalability beyond pulling back thousands of rows in one big gulp. And, if your data can be worked on in part (i.e. without having the entire set in memory), you could send off chunks to be worked on in a separate thread while you are pulling back the next chunk.