Weird timeout issues with Dapper.net

dapper database-performance sql

Question

I started to use dapper.net a while ago for performance reasons and that i really like the named parameters feature compared to just run "ExecuteQuery" in LINQ To SQL.

It works great for most queries but i get some really weird timeouts from time to time. The strangest thing is that this timeout only happens when the SQL is executed via dapper. If i take the executed query copied from the profiler and just run it in Management Studio its fast and works perfect. And it's not just a temporary issues. The query consistently timeout via dapper and consistently works fine in Management Studio.

exec sp_executesql N'SELECT Item.Name,dbo.PlatformTextAndUrlName(Item.ItemId) As PlatformString,dbo.MetaString(Item.ItemId) As MetaTagString, Item.StartPageRank,Item.ItemRecentViewCount
                    NAME_SRCH.RANK as NameRank,
                    DESC_SRCH.RANK As DescRank, 
                    ALIAS_SRCH.RANK as AliasRank, 
                    Item.itemrecentviewcount,
                    (COALESCE(ALIAS_SRCH.RANK, 0)) + (COALESCE(NAME_SRCH.RANK, 0)) + (COALESCE(DESC_SRCH.RANK, 0) / 20) + Item.itemrecentviewcount / 4 + ((CASE WHEN altrank > 60 THEN 60 ELSE altrank END) * 4) As SuperRank
                    FROM dbo.Item
                    INNER JOIN dbo.License on Item.LicenseId = License.LicenseId

                    LEFT JOIN dbo.Icon on Item.ItemId = Icon.ItemId
                    LEFT OUTER JOIN FREETEXTTABLE(dbo.Item, name, @SearchString) NAME_SRCH ON
                    Item.ItemId = NAME_SRCH.[KEY] 
                    LEFT OUTER JOIN FREETEXTTABLE(dbo.Item, namealiases, @SearchString) ALIAS_SRCH ON
                    Item.ItemId = ALIAS_SRCH.[KEY] 
                    INNER JOIN FREETEXTTABLE(dbo.Item, *, @SearchString) DESC_SRCH ON
                    Item.ItemId = DESC_SRCH.[KEY]
                    ORDER BY SuperRank DESC OFFSET @Skip ROWS FETCH NEXT @Count ROWS ONLY',N'@Count int,@SearchString nvarchar(4000),@Skip int',@Count=12,@SearchString=N'box,com',@Skip=0

That is the query that i copy pasted from SQL Profiler. I execute it like this in my code.

            using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString())) {
            connection.Open();
            var items = connection.Query<MainItemForList>(query, new { SearchString = searchString, PlatformId = platformId, _LicenseFilter = licenseFilter, Skip = skip, Count = count }, buffered: false);
            return items.ToList();
        }

I have no idea where to start here. I suppose there must be something that is going on with dapper since it works fine when i just execute the code.

As you can see in this screenshot. This is the same query executed via code first and then via Management Studio.

enter image description here

I can also add that this only (i think) happens when i have two or more word or when i have a "stop" char in the search string. So it may have something todo with the full text search but i cant figure out how to debug it since it works perfectly from Management Studio.

And to make matters even worse, it works fine on my localhost with a almost identical database both from code and from Management Studio.

Accepted Answer

Dapper is nothing more than a utility wrapper over ado.net; it does not change how ado.net operates. It sounds to me that the problem here is "works in ssms, fails in ado.net". This is not unique: it is pretty common to find this occasionally. Likely candidates:

  • "set" option: these have different defaults in ado.net - and can impact performance especially if you have things like calculated+persisted+indexed columns - if the "set" options aren't compatible it can decide it can't use the stored value, hence not the index - and instead table-scan and recompute. There are other similar scenarios.
  • system load / transaction isolation-level / blocking; running something in ssms does not reproduce the entire system load at that moment in time
  • cached query plans: sometimes a duff plan gets cached and used; running from ssms will usually force a new plan - which will naturally be tuned for the parameters you are using in your test. Update all your index stats etc, and consider adding the "optimise for" query hint

Popular Answer

In ADO is the default value for CommandTimeout 30 Seconds, in Management Studio infinity. Adjust the command timeout for calling Query<>, see below.

var param = new { SearchString = searchString, PlatformId = platformId, _LicenseFilter = licenseFilter, Skip = skip, Count = count };
var queryTimeoutInSeconds = 120;
using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString()))
{
    connection.Open();
    var items = connection.Query<MainItemForList>(query, param, commandTimeout: queryTimeoutInSeconds, buffered: false);
    return items.ToList();
}

See also SqlCommand.CommandTimeout Property on MSDN




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