I have a winforms app where I have a Telerik dropdownchecklist that lets the user select a group of state names.
Using EF and the database is stored in Azure SQL.
The code then hits a database of about 17,000 records and filters the results to only include states that are checked.
Works fine. I am wanting to update a count on the screen whenever they change the list box.
This is the code, in the itemCheckChanged event:
var states = stateDropDownList.CheckedItems.Select(i => i.Value.ToString()).ToList();
var filteredStops = (from stop in aDb.Stop_address_details where states.Contains(stop.Stop_state) select stop).ToArray();
ExportInfo_tb.Text = "Current Stop Count: " + filteredStops.Count();
It works, but it is slow.
I tried to load everything into a memory variable then querying that vs the database but can't seem to figure out how to do that.
Any suggestions?
Improvement:
I picked up a noticeable improvement by limiting the amount of data coming down by:
var filteredStops = (from stop in aDb.Stop_address_details where states.Contains(stop.Stop_state) select stop.Stop_state).ToList();
And better yet --
int count = (from stop in aDb.Stop_address_details where
states.Contains(stop.Stop_state)
select stop).Count();
ExportInfo_tb.Text = "Current Stop Count: " + count.ToString();
The performance of you query, actually, has nothing to do with Contiains, in this case. Contains is pretty performant. The problem, as you picked up on in your third solution, is that you are pulling far more data over the network than required.
In your first solution you are pulling back all of the rows from the server with the matching stop state and performing the count locally. This is the worst possible approach. You are pulling back data just to count it and you are pulling back far more data than you need.
In your second solution you limited the data coming back to a single field which is why the performance improved. This could have resulted in a significant improvement if your table is really wide. The problem with this is that you are still pulling back all the data just to count it locally.
In your third solution EF will translate the .Count() method into a query that performs the count for you. So the count will happen on the server and the only data returned is a single value; the result of count. Since network latency CAN often be (but is not always) the longest step when performing a query, returning less data can often result in significant gains in query speed.
The query translation of your final solution should look something like this:
SELECT COUNT(*) AS [value]
FROM [Stop_address_details] AS [t0]
WHERE [t0].[Stop_state] IN (#p0)
Related
My data model has an entity Person with 3 related (1:N) entities Jobs, Tasks and Dates.
My query looks like
var persons = (from x in context.Persons
select new {
PersonId = x.Id,
JobNames = x.Jobs.Select(y => y.Name),
TaskDates = x.Tasks.Select(y => y.Date),
DateInfos = x.Dates.Select(y => y.Info)
}).ToList();
Everything seems to work fine, but the lists JobNames, TaskDates and DateInfos are not all filled.
For example, TaskDates and DateInfos have the correct values, but JobNames stays empty. But when I remove TaskDates from the query, then JobNames is correctly filled.
So it seems that EF can only handle a limited number of these "subqueries"? Is this correct? If so, what is the max. number of these "subqueries" for a single statement? Is there a way to work around these issue without having to make more than one call to the database?
(ps: I'm not entirely sure, but I seem to remember that this query worked in LINQ2SQL - could it be?)
UPDATE
I'm getting crazy about this. I tried to repro the issue from ground up using a fresh, simple project (to post the entire piece of code here, not only an oversimplified example) - and I found I wasn't able to repro it. It still happens within our existing code base (apparently there's more behind this problem, but I cannot share this closed code base, unfortunately).
After hours and hours of playing around I found the weirdest behavior:
It works great when I don't SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED; before calling the LINQ statement
It also works great (independent of the above) when I don't use a .Take() to only get the first X rows
It also works great when I add an additional .Where() statements to cut the the number of rows returned from SQL Server
I didn't find any comprehensible reason why I see this behavior, but I started to look at the SQL: Although EF generates the exact same SQL, the execution plan is different when I use READ UNCOMMITTED. It returns more rows on a specific index in the middle of the execution plan, which curiously ends in less rows returned for the entire SQL statement - which in turn results in the missing data, that is the reason for my question to begin with.
This sounds very confusing and unbelievable, I know, but this is the behavior I see. I don't know what else to do, I don't even know what to google for at this point ;-).
I can fix my problem (just don't use READ UNCOMMITTED), but I have no idea why it occurs and if it is a bug or something I don't know about SQL Server. Maybe there's some "magic max number of allowed results in sub-queries" in SQL Server? At least: As far as I can see, it's not an issue with EF itself.
A little late, but does calling ToList() on each subquery produce the required effect?
var persons = (from x in context.Persons
select new {
PersonId = x.Id,
JobNames = x.Jobs.Select(y => y.Name.ToList()),
TaskDates = x.Tasks.Select(y => y.Date).ToList(),
DateInfos = x.Dates.Select(y => y.Info).ToList()
}).ToList();
I executed some query like "Address:Jack*". It show numFound = 5214 and display 100 documents in results page(I changed default display results from 10 to 100).
How can I get all documents.
I remember myself doing &rows=2147483647
2,147,483,647 is integer's maximum value. I recall using a number bigger than that once and having a NumberFormatException because it couldn't be parsed into an int. I don't know if they use Long nowadays, but 2 billion rows is normally more than enough.
Small note:
Be careful if you are planning to do this in production. If you do a query like * : * and your index is big, you could transferring a couple of gigabytes in that query.
If you know you won't have many docs, go ahead and use integer's max value.
On the other hand, if you are doing a one-time script and just need to dump all results (for example document ID's) then this approach is valid, if you don't mind waiting 3-5 minutes for a query to return.
Don't use &rows=2147483647
Don't use Integer.MAX_VALUE(2147483647) as value of rows in production. This will heavily slow down your query even if you have a small resultset, because solr preallocates a queue in this size. see https://issues.apache.org/jira/browse/SOLR-7580
I strongly suggest to use Exporting Result Sets
It’s possible to export fully sorted result sets using a special rank query parser and response writer specifically designed to work together to handle scenarios that involve sorting and exporting millions of records.
Or I suggest to use Deep Paging.
Simple Pagination is a easy thing when you have few documents to read and all you have to do is play with start and rows parameters. But this is not a feasible way when you have many documents, I mean hundreds of thousands or even millions.
This is the kind of thing that could bring your Solr server to their knees.
For typical applications displaying search results to a human user,
this tends to not be much of an issue since most users don’t care
about drilling down past the first handful of pages of search results
— but for automated systems that want to crunch data about all of the
documents matching a query, it can be seriously prohibitive.
This means that if you have a website and are paging search results, a real user do not go so further but consider on the other hand what can happen if a spider or a scraper try to read all the website pages.
Now we are talking of Deep Paging.
I’ll suggest to read this amazing post:
https://lucidworks.com/post/coming-soon-to-solr-efficient-cursor-based-iteration-of-large-result-sets/
And take a look at this document page:
https://solr.apache.org/guide/pagination-of-results.html
And here is an example that try to explain how to paginate using the cursors.
SolrQuery solrQuery = new SolrQuery();
solrQuery.setRows(500);
solrQuery.setQuery("*:*");
solrQuery.addSort("id", ORDER.asc); // Pay attention to this line
String cursorMark = CursorMarkParams.CURSOR_MARK_START;
boolean done = false;
while (!done) {
solrQuery.set(CursorMarkParams.CURSOR_MARK_PARAM, cursorMark);
QueryResponse rsp = solrClient.query(solrQuery);
String nextCursorMark = rsp.getNextCursorMark();
for (SolrDocument d : rsp.getResults()) {
...
}
if (cursorMark.equals(nextCursorMark)) {
done = true;
}
cursorMark = nextCursorMark;
}
Returning all the results is never a good option as It would be very slow in performance.
Can you mention your use case ?
Also, Solr rows parameter helps you to tune the number of the results to be returned.
However, I don't think there is a way to tune rows to return all results. It doesn't take a -1 as value.
So you would need to set a high value for all the results to be returned.
What you should do is to first create a SolrQuery shown below and set the number of documents you want to fetch in a batch.
int lastResult=0; //this is for processing the future batch
String query = "id:[ lastResult TO *]"; // just considering id for the sake of simplicity
SolrQuery solrQuery = new SolrQuery(query).setRows(500); //setRows will set the required batch, you can change this to whatever size you want.
SolrDocumentList results = solrClient.query(solrQuery).getResults(); //execute this statement
Here I am considering an example of search by id, you can replace it with any of your parameter to search upon.
The "lastResult" is the variable you can change after execution of the first 500 records(500 is the batch size) and set it to the last id got from the results.
This will help you execute the next batch starting with last result from previous batch.
Hope this helps. Shoot up a comment below if you need any clarification.
For selecting all documents in dismax/edismax via Solarium php client, the normal query syntax : does not work. To select all documents set the default query value in solarium query to empty string. This is required as the default query in Solarium is :. Also set the alternative query to :. Dismax/eDismax normal query syntax does not support :, but the alternative query syntax does.
For more details following book can be referred
http://www.packtpub.com/apache-solr-php-integration/book
As the other answers pointed out, you can configure the rows to be max integer to yield back all the results for a query.
I would recommend though to use Solr feature of pagination, and build a function that will return for you all the results using the cursorMark API. The gist of it is you set the cursorMark parameter to '*', you set the page size(rows parameter), and on each result you'll get a cursorMark for the next page, so you execute the same query only with the cursorMark given from the last result. This way you'll have more flexibility on how much of the results you want back, in a much more performant way.
The way I dealt with the problem is by running the query twice:
// Start with your (usually small) default page size
solrQuery.setRows(50);
QueryResponse response = solrResponse(query);
if (response.getResults().getNumFound() > 50) {
solrQuery.setRows(response.getResults().getNumFound());
response = solrResponse(query);
}
It makes a call twice to Solr, but gets you all matching records....with the small performance penalty.
query.setRows(Integer.MAX_VALUE);
works for me!!
I have some Django 1.3 code that looks up many model instances in a loop, ie.
my_set = myinstance.subitem_set.all()
for value in values:
existing = my_set.filter(attr_name=value)
if len(existing) == 1:
...
This works, but profiling SQL queries shows that it hits the DB on each iteration. According to https://docs.djangoproject.com/en/1.3/ref/models/querysets/ iterating over the related items should eagerly load them, so I tried calling:
list(my_set)
However, this doesn't help. It does do a query to load all the sub-items, but then it still does an individual query for each sub-item inside the loop. How do I get it to use the cached set and not hit the DB each time? The DB is PostgreSQL 8.4.
The problem is in this line:
if len(existing) == 1:
From Django documentation:
len(). A QuerySet is evaluated when you call len() on it. This, as you might expect, returns the length of the result list.
Note: Don't use len() on QuerySets if all you want to do is determine the number of records in the set. It's much more efficient to handle a count at the database level, using SQL's SELECT COUNT(*), and Django provides a count() method for precisely this reason. See count() below.
So in your case it executes the query each time when you call len(existing). The more effective way is:
existing.count() == 1
This will also hit the database each time you call it but it will execute SELECT COUNT(*) which is faster.
I'm writing an NHibernate criteria that selects data supporting paging. I'm using the COUNT(*) OVER() expression from SQL Server 2005(+) to get hold of the total number of available rows, as suggested by Ayende Rahien. I need that number to be able to calculate how many pages there are in total. The beauty of this solution is that I don't need to execute a second query to get hold of the row count.
However, I can't seem to manage to write a working criteria (Ayende only provides an HQL query).
Here's an SQL query that shows what I want and it works just fine. Note that I intentionally left out the actual paging logic to focus on the problem:
SELECT Items.*, COUNT(*) OVER() AS rowcount
FROM Items
Here's the HQL:
select
item, rowcount()
from
Item item
Note that the rowcount() function is registered in a custom NHibernate dialect and resolves to COUNT(*) OVER() in SQL.
A requirement is that the query is expressed using a criteria. Unfortunately, I don't know how to get it right:
var query = Session
.CreateCriteria<Item>("item")
.SetProjection(
Projections.SqlFunction("rowcount", NHibernateUtil.Int32));
Whenever I add a projection, NHibernate doesn't select item (like it would without a projection), just the rowcount() while I really need both. Also, I can't seem to project item as a whole, only it's properties and I really don't want to list all of them.
I hope someone has a solution to this. Thanks anyway.
I think it is not possible in Criteria, it has some limits.
You could get the id and load items in a subsequent query:
var query = Session
.CreateCriteria<Item>("item")
.SetProjection(Projections.ProjectionList()
.Add(Projections.SqlFunction("rowcount", NHibernateUtil.Int32))
.Add(Projections.Id()));
If you don't like it, use HQL, you can set the maximal number of results there too:
IList<Item> result = Session
.CreateQuery("select item, rowcount() from item where ..." )
.SetMaxResult(100)
.List<Item>();
Use CreateMultiCriteria.
You can execute 2 simple statements with only one hit to the DB that way.
I am wondering why using Criteria is a requirement. Can't you use session.CreateSQLQuery? If you really must do it in one query, I would have suggested pulling back the Item objects and the count, like:
select {item.*}, count(*) over()
from Item {item}
...this way you can get back Item objects from your query, along with the count. If you experience a problem with Hibernate's caching, you can also configure the query spaces (entity/table caches) associated with a native query so that stale query cache entries will be cleared automatically.
If I understand your question properly, I have a solution. I struggled quite a bit with this same problem.
Let me quickly describe the problem I had, to make sure we're on the same page. My problem came down to paging. I want to display 10 records in the UI, but I also want to know the total number of records that matched the filter criteria. I wanted to accomplish this using the NH criteria API, but when adding a projection for row count, my query no longer worked, and I wouldn't get any results (I don't remember the specific error, but it sounds like what you're getting).
Here's my solution (copy & paste from my current production code). Note that "SessionError" is the name of the business entity I'm retrieving paged data for, according to 3 filter criterion: IsDev, IsRead, and IsResolved.
ICriteria crit = CurrentSession.CreateCriteria(typeof (SessionError))
.Add(Restrictions.Eq("WebApp", this));
if (isDev.HasValue)
crit.Add(Restrictions.Eq("IsDev", isDev.Value));
if (isRead.HasValue)
crit.Add(Restrictions.Eq("IsRead", isRead.Value));
if (isResolved.HasValue)
crit.Add(Restrictions.Eq("IsResolved", isResolved.Value));
// Order by most recent
crit.AddOrder(Order.Desc("DateCreated"));
// Copy the ICriteria query to get a row count as well
ICriteria critCount = CriteriaTransformer.Clone(crit)
.SetProjection(Projections.RowCountInt64());
critCount.Orders.Clear();
// NOW add the paging vars to the original query
crit = crit
.SetMaxResults(pageSize)
.SetFirstResult(pageNum_oneBased * pageSize);
// Set up a multi criteria to get your data in a single trip to the database
IMultiCriteria multCrit = CurrentSession.CreateMultiCriteria()
.Add(crit)
.Add(critCount);
// Get the results
IList results = multCrit.List();
List<SessionError> sessionErrors = new List<SessionError>();
foreach (SessionError sessErr in ((IList)results[0]))
sessionErrors.Add(sessErr);
numResults = (long)((IList)results[1])[0];
So I create my base criteria, with optional restrictions. Then I CLONE it, and add a row count projection to the CLONED criteria. Note that I clone it before I add the paging restrictions. Then I set up an IMultiCriteria to contain the original and cloned ICriteria objects, and use the IMultiCriteria to execute both of them. Now I have my paged data from the original ICriteria (and I only dragged the data I need across the wire), and also a raw count of how many actual records matched my criteria (useful for display or creating paging links, or whatever). This strategy has worked well for me. I hope this is helpful.
I would suggest investigating custom result transformer by calling SetResultTransformer() on your session.
Create a formula property in the class mapping:
<property name="TotalRecords" formula="count(*) over()" type="Int32" not-null="true"/>;
IList<...> result = criteria.SetFirstResult(skip).SetMaxResults(take).List<...>();
totalRecords = (result != null && result.Count > 0) ? result[0].TotalRecords : 0;
return result;
So, I have an autocomplete dropdown with a list of townships. Initially I just had the 20 or so that we had in the database... but recently, we have noticed that some of our data lies in other counties... even other states. So, the answer to that was buy one of those databases with all towns in the US (yes, I know, geocoding is the answer but due to time constraints we are doing this until we have time for that feature).
So, when we had 20-25 towns the autocomplete worked stellarly... now that there are 80,000 it's not as easy.
As I type I am thinking that the best way to do this is default to this state, then there will be much less. I will add a state selector to the page that defaults to NJ then you can pick another state if need be, this will narrow down the list to < 1000. Though, I may have the same issue? Does anyone know of a work around for an autocomplete with a lot of data?
should I post teh codez of my webservice?
Are you trying to autocomplete after only 1 character is typed? Maybe wait until 2 or more...?
Also, can you just return the top 10 rows, or something?
Sounds like your application is suffocating on the amount of data being returned, and then attempted to be rendered by the browser.
I assume that your database has the proper indexes, and you don't have a performance problem there.
I would limit the results of your service to no more than say 100 results. Users will not look at any more than that any how.
I would also only being retrieving the data from the service once 2 or 3 characters are entered which will further reduce the scope of the query.
Good Luck!
Stupid question maybe, but... have you checked to make sure you have an index on the town name column? I wouldn't think 80K names should be stressing your database...
I think you're on the right track. Use a series of cascading inputs, State -> County -> Township where each succeeding one grabs the potential population based on the value of the preceding one. Each input would validate against its potential population to avoid spurious inputs. I would suggest caching the intermediate results and querying against them for the autocomplete instead of going all the way back to the database each time.
If you have control of the underlying SQL, you may want to try several "UNION" queries instead of one query with several "OR like" lines in its where clause.
Check out this article on optimizing SQL.
I'd just limit the SQL query with a TOP clause. I also like using a "less than" instead of a like:
select top 10 name from cities where #partialname < name order by name;
that "Ce" will give you "Cedar Grove" and "Cedar Knolls" but also "Chatham" & "Cherry Hill" so you always get ten.
In LINQ:
var q = (from c in db.Cities
where partialname < c.Name
orderby c.Name
select c.Name).Take(10);