From [**Microsoft documentation**](https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-os-wait-stats-transact-sql):

&gt; `PAGEIOLATCH_SH`
&gt;
&gt;  Occurs when a task is waiting on a latch for a buffer that is in an `I/O` request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.

In practice, this almost always happens due to large scans over big tables. It almost never happens in queries that use indexes efficiently.

If your query is like this:

    Select * from &lt;table&gt; where &lt;col1&gt; = &lt;value&gt; order by &lt;PrimaryKey&gt;

, check that you have a composite index on `(col1, col_primary_key)`.

If you don&#39;t have one, then you&#39;ll need either a full `INDEX SCAN` if the `PRIMARY KEY` is chosen, or a `SORT` if an index on `col1` is chosen.

Both of them are very disk `I/O` consuming operations on large tables.

`PAGEIOLATCH_SH` wait type usually comes up as the result of fragmented or unoptimized index.

Often reasons for excessive `PAGEIOLATCH_SH` wait type are:

- I/O subsystem has a problem or is misconfigured
- Overloaded I/O subsystem by other processes that are producing the high I/O activity
- Bad index management
- Logical or physical drive misconception
- Network issues/latency
- Memory pressure
- Synchronous Mirroring and AlwaysOn AG

In order to try and resolve having high `PAGEIOLATCH_SH` wait type, you can check:

- SQL Server, queries and indexes, as very often this could be found as a root cause of the excessive `PAGEIOLATCH_SH` wait types
- For memory pressure before jumping into any I/O subsystem troubleshooting

Always keep in mind that in case of high safety Mirroring or synchronous-commit availability in AlwaysOn AG, increased/excessive `PAGEIOLATCH_SH` can be expected.

You can find more details about this topic in the article [Handling excessive SQL Server PAGEIOLATCH_SH wait types](https://www.sqlshack.com/handling-excessive-sql-server-pageiolatch_sh-wait-types/)



I have tried this is RC1 and then upgraded to RC2 which did not resolve the issue.

    // in my controller
    ViewData[&quot;UserId&quot;] = new SelectList(
        users, 
        &quot;UserId&quot;, 
        &quot;DisplayName&quot;, 
        selectedUserId.Value); // this has a value
    
result: the SelectedValue property is set on the object

    // in my view
    &lt;%=Html.DropDownList(&quot;UserId&quot;, (SelectList)ViewData[&quot;UserId&quot;])%&gt;

result: all expected options are rendered to the client, but the selected attribute is not set.  The item in SelectedValue exists within the list, but the first item in the list is always defaulted to selected.

How should I be doing this?

**Update**
Thanks to John Feminella&#39;s reply I found out what the issue is.  &quot;UserId&quot; is a property in the Model my View is strongly typed to.  When Html.DropDownList(&quot;UserId&quot; is changed to any other name but &quot;UserId&quot;, the selected value is rendered correctly. 

This results in the value not being bound to the model though.

ASP.NET MVC Html.DropDownList SelectedValue

I have a problem controlling the width of a table using the jQuery DataTables plugin.  The table is supposed to be 100% of the container width, but ends up being an arbitrary width, rather less than the container width.

Suggestions appreciated

The table declaration looks like this

    &lt;table id=&quot;querytableDatasets&quot; class=&quot;display&quot; cellspacing=&quot;0&quot;
    cellpadding=&quot;3&quot;     width=&quot;100%&quot;&gt;

And the javascript

    jQuery(&#39;#tab-datasets&#39;).load(&#39;/cgi-bin/qryDatasets&#39;, &#39;&#39;, function (){  
        jQuery(&#39;#querytableDatasets&#39;).dataTable({  
            &quot;bPaginate&quot;: false,  
            &quot;bInfo&quot;: false,  
            &quot;bFilter&quot;: false  
        });  
    });  `  


Inspecting the HTML in Firebug, you see this (note the added style=&quot;width: 0px;&quot;)

    &lt;table id=&quot;querytableDatasets&quot; class=&quot;display&quot; cellspacing=&quot;0&quot; 
    cellpadding=&quot;3&quot; width=&quot;100%&quot; style=&quot;width: 0px;&quot;&gt;

Looking in Firebug at the styles, the table.display style has been overridden.  Can&#39;t see where this is coming from

    element.style {  
      width:0;}    
    
    -- dataTables.css (line 84
    table.display { 
      margin:0 auto;  
      width:100%;  
    }  



jQuery DataTables: control table width

I have a query that is taking a long time in the middle of a transaction. When I get the `wait_type` of the process it is `PAGEIOLATCH_SH`. 

What does this wait type mean and how can this be resolved?

What is PAGEIOLATCH_SH wait type in SQL Server?

<p>I have a query that is taking a long time in the middle of a transaction. When I get the <code>wait_type</code> of the process it is <code>PAGEIOLATCH_SH</code>.</p>
<p>What does this wait type mean and how can this be resolved?</p>


I am trying to change a column from a `varchar(50)` to a `nvarchar(200)`. What is the SQL command to alter this table? 

How do you change the datatype of a column in SQL Server?

I downloaded [SQL Server 2008][1] and can&#39;t seem to find [SQL Profiler][2] anywhere.

I believe I installed the SQL Server Enterprise Express/trial version?

I guess it was Express and not Enterprise after all right?

  [1]: http://en.wikipedia.org/wiki/Microsoft_SQL_Server#SQL_Server_2008
  [2]: http://msdn.microsoft.com/en-us/library/aa173918%28SQL.80,printer%29.aspx


Where is SQL Profiler in my SQL Server 2008?

I have a table like this:

    rowInt  Value
    2       23
    3       45
    17      10
    9       0
    ....

The column rowInt values are integer but not in a sequence with same increament. I can use the following sql to list values by rowInt:

    SELECT * FROM myTable ORDER BY rowInt;

This will list values by rowInt. How can get get the difference of Value between two rows with the result like this:

    rowInt   Value Diff
    2        23    22    --45-23
    3        45    -35   --10-45
    9        0     -45   --0-45
    17       10    10    -- 10-0
    ....

The table is in SQL 2005 (Miscrosoft)

How to get difference between two rows for a column field?

I need to write a T-SQL stored procedure that updates a row in a table. If the row doesn&#39;t exist, insert it. All this steps wrapped by a transaction. 

This is for a booking system, so it must be **atomic and reliable**. It must return true if the transaction was committed and the flight booked.

I&#39;m **new to T-SQL**, and not sure on how to use `@@rowcount`. This is what I&#39;ve written until now. Am I on the right road? I&#39;m sure is an easy problem for you.

    -- BEGIN TRANSACTION (HOW TO DO?)
    	
    UPDATE Bookings
     SET TicketsBooked = TicketsBooked + @TicketsToBook
     WHERE FlightId = @Id AND TicketsMax &lt; (TicketsBooked + @TicketsToBook)
    
    -- Here I need to insert only if the row doesn&#39;t exists.
    -- If the row exists but the condition TicketsMax is violated, I must not insert 
    -- the row and return FALSE

    IF @@ROWCOUNT = 0 
    BEGIN
    
     INSERT INTO Bookings ... (omitted)
              	   
    END
    
    -- END TRANSACTION (HOW TO DO?)

    -- Return TRUE (How to do?)



Check if a row exists, otherwise insert

Trying to understand what Sql Profiler means by emitting &quot;sp_reset_connection&quot;.

I have the following, &quot;exec sp_reset_connection&quot; line followed by BatchStarting and Completed,

    RPC:Completed	    exec sp_reset_connection
    SQL:BatchStarting   SELECT [c].[TestID] AS [TestID], [c].[Description] AS [Description] FROM [dbo].[Test] AS [c]
    SQL:BatchCompleted  SELECT [c].[TestID] AS [TestID], [c].[Description] AS [Description] FROM [dbo].[Test] AS [c]	

Basically does first line &quot;exec sp_reset_connection&quot; mean the whole process (my connection was opened, the select stmt is run, then the connection is closed and released back to pool) just take place?  Or my connection is still in open stage.

And, why does the sp_reset_connection executed before my own select statement, shouldn&#39;t it the reset come after user&#39;s sql?

I&#39;m trying to know is there a way to know in more detail when a connection is opened and closed?

By seeing &quot;exec sp_reset_connection&quot;, does that mean my connection is closed?


What does &quot;exec sp_reset_connection&quot; mean in Sql Server Profiler?

Pretty simple question - I have an attribute that I would like to have double quotes in.  How do I escape them?  I&#39;ve tried

 - \&quot;
 - &quot;&quot;
 - \\\&quot;

And I&#39;ve made the @xml variable both xml type and varchar(max) for all of them.

     declare @xml xml --(or varchar(max) tried both)
     
     set @xml = &#39;&lt;transaction&gt;&lt;item value=&quot;hi &quot;mom&quot; lol&quot; 
     	ItemId=&quot;106&quot;  ItemType=&quot;2&quot;  instanceId=&quot;215923801&quot;  dataSetId=&quot;1&quot; /&gt;&lt;/transaction&gt;&#39;
     
     declare @xh int
     exec sp_xml_preparedocument @xh OUTPUT, @xml
     
     insert into @commits --I declare the table, just removed it for brevity
     select
     	x.*
     from openxml(@xh,&#39;/transaction/item&#39;)
      WITH (
     	dataItemId int,
         dataItemType int,
     	instanceId int,
     	dataSetId int,
     	value varchar(max)
      ) x

How do I escape double quotes in attributes in an XML String in T-SQL?

How do I do a `SELECT * INTO [temp table] FROM [stored procedure]`? Not `FROM [Table]` and without defining `[temp table]`?

`Select` all data from `BusinessLine` into `tmpBusLine` works fine.

    select *
    into tmpBusLine
    from BusinessLine

I am trying the same, but using a `stored procedure` that returns data, is not quite the same.

    select *
    into tmpBusLine
    from
    exec getBusinessLineHistory &#39;16 Mar 2009&#39;

**Output message:**

&gt; Msg 156, Level 15, State 1, Line 2
&gt; Incorrect syntax near the keyword
&gt; &#39;exec&#39;.

I have read several examples of creating a temporary table with the same structure as the output stored procedure, which works fine, but it would be nice to not supply any columns.


Insert results of a stored procedure into a temporary table

I have a Java program that stores a lot of mappings from Strings to various objects. 

Right now, my options are either to rely on hashing (via HashMap) or on binary searches (via TreeMap). I am wondering if there is an efficient and standard trie-based map implementation in a popular and quality collections library?

I&#39;ve written my own in the past, but I&#39;d rather go with something standard, if available.

Quick clarification: While my question is general, in the current project I am dealing with a lot of data that is indexed by fully-qualified class name or method signature. Thus, there are many shared prefixes. 

Where do I find a standard Trie based map implementation in Java?

I would like to know what *copy-on-write* is and what it is used for. The term is mentioned several times in the Sun JDK tutorials.

What is copy-on-write?

At Disney World, they use a system called [Fastpass][1] to create a second, shorter line for popular rides.  The idea is that you can wait in the standard line, often with a wait longer than an hour, or you can get a FastPass which allows you to come back during a specified time block (usually a couple hours later) and only wait for 10 minutes or less.  You can only be &quot;waiting&quot; for one ride at a time with a FastPass.

I have been trying to figure out the queue theory behind this concept, but the only explanation I have found is that it is designed to get people out of the lines and doing things that will bring in additional revenue (shopping, eating, etc).  

Is this why FastPass was implemented, or is there a real visitor efficiency problem that it solving?  Are there software applications that have applied similar logic?  Are there software applications that *should* apply similar logic?

Part of the problem I see with implementing something similar in software is that it is based on users choosing their queue.  Do to the faster wait cycles in software, I think a good application of this theory would require the application to be smart enough to know what queues to place people in based on their needs without requiring end-user choice.

**UPDATE**

12 years (and two major updates to FastPass later), [Disney&#39;s FastPass: A Complicated History][2] gives the in-depth, definitive answer of &quot;it&#39;s complicated&quot;


  [1]: http://en.wikipedia.org/wiki/FASTPASS
  [2]: https://youtu.be/9yjZpBq1XBE

Is Disney&#39;s FastPass Valid and/or Useful Queue Theory

Is there a simple tutorial for me to get up to speed in SSE, SSE2 and SSE3 in GNU C++?  How can you do code optimization in SSE?

SSE SSE2 and SSE3 for GNU C++

If I have some integer n, and I want to know the position of the most significant bit (that is, if the least significant bit is on the right, I want to know the position of the furthest left bit that is a 1), what is the quickest/most efficient method of finding out?

I know that POSIX supports a `ffs()` method in strings.h to find the first set bit, but there doesn&#39;t seem to be a corresponding `fls()` method.

Is there some really obvious way of doing this that I&#39;m missing?

What about in cases where you can&#39;t use POSIX functions for portability?

Edit: What about a solution that works on both 32 and 64 bit architectures (many of the code listings seem like they&#39;d only work on 32 bit ints).

Content Type	Original Author	Original Content on Stackoverflow
Question	Ryan	View Question on Stackoverflow
Solution 1 - Sql Server	Quassnoi	View Answer on Stackoverflow
Solution 2 - Sql Server	G.Hunt	View Answer on Stackoverflow

What is PAGEIOLATCH_SH wait type in SQL Server?

Sql Server Problem Overview

Sql Server Solutions

Solution 1 - Sql Server

Solution 2 - Sql Server

jQuery DataTables: control table width

ASP.NET MVC Html.DropDownList SelectedValue

Attributions