System Tables - sys.processes

Analyse current processes with sysprocesses

The following SQL is based on an article about the sys.processes system view on SQLServerCentral I read today and is another good example of using SQL system views and the new DMV's (Data Management Views).

I have combined some of the example code from the article into a helpful query for analysing your current processes to find long running queries that maybe causing issues with your system. Read the comments within the code for more details.

-- Using the sys.processes system table to find current process details

DECLARE @oldStats TABLE( os_thread_id int, kernel_time bigint, usermode_time bigint)

/* Insert current threads

The KPID is useful in that it helps us tie up what has been passed to the operating system to run commands and is actually working.
Although the SPID is constant throughout the life of the connection a KPID is allocated to each task that needs to be carried out.

The KPID maps back to an actual windows thread and so it is possible using performance monitor to get actual physical statistics
about a task instead of the purely logical statistics which SQL shows through the CPU column.

The KPID is the actual o/s thread id and you can use the "Thread" performance counter using "ID Thread" and "% Processor Time" to
match the thread to the actual cpu stats.
*/
INSERT INTO @oldStats
SELECT os_thread_id, kernel_time, usermode_time
FROM sys.dm_os_threads
WHERE os_thread_id IN (SELECT KPID
FROM sys.sysprocesses
WHERE kpid <> 0
 AND spid>50)

-- wait for 2 seconds
WAITFOR DELAY '0:0:2'

/* Compare previous data to our current processes to see which task are consuming
the most CPU.

If records appear with a KPID of 0 and Physical Time of NULL then it means the
O/S thread is no longer active.

Investigate processes that have high physical times, high CPU, long wait times, and blocked
*/
SELECT sp.KPID, sp.SPID, sp.CPU AS LogicalCPU
,(new.kernel_time + new.usermode_time) - (old.kernel_time + old.usermode_time) AS PhysicalTime
,waittime,lastwaittype,blocked
,blockingSQL = CASE WHEN blocked > 0 AND blocked <> sp.SPID THEN  (SELECT SUBSTRING((SELECT TEXT FROM fn_get_sql(sql_handle)), stmt_start/2,
CASE stmt_end
WHEN -1 THEN LEN(CONVERT(VARCHAR(8000), (SELECT TEXT FROM fn_get_sql(sql_handle)))) - (stmt_end/2)
WHEN 0 THEN LEN(CONVERT(VARCHAR(8000), (SELECT TEXT FROM fn_get_sql(sql_handle))))
ELSE stmt_end /2
END
) FROM sys.sysprocesses WHERE SPID = sp.blocked) ELSE NULL END
,last_batch,open_tran,sp.status,loginame,hostname,cmd
,(SELECT SUBSTRING((SELECT TEXT FROM fn_get_sql(sql_handle)), stmt_start/2,
CASE stmt_end
WHEN -1 THEN LEN(CONVERT(VARCHAR(8000), (SELECT TEXT FROM fn_get_sql(sql_handle)))) - (stmt_end/2)
WHEN 0 THEN LEN(CONVERT(VARCHAR(8000), (SELECT TEXT FROM fn_get_sql(sql_handle))))
ELSE stmt_end /2
END
) FROM sys.sysprocesses WHERE SPID = sp.SPID) as TSQL
FROM sys.sysprocesses SP
LEFT OUTER JOIN
@oldStats old
ON SP.kpid = old.os_thread_id
LEFT OUTER JOIN
sys.dm_os_threads new
ON sp.kpid = new.os_thread_id
ORDER BY PhysicalTime DESC

Store and Analyse Blocked Processes

To view your blocked processes in more detail either set up a loop with a WAITFOR DELAY or an MS Agent job that runs once a minute to log into a table the output from the following SQL. The SQL make use of a recursive CTE to link together all the processes affected by a blocking action which is useful for seeing the action that has caused the blocking and all the processes being affected by the blocking. You can view all databases on the server or filter by a particular database name or partial name.

DECLARE @DatabaseName nvarchar(255) --leave null to use current DB OR 'ALL' For all DBS
DECLARE @PROCESSES TABLE(SPID int, blockingSPID int, databaseName nvarchar(255), programName nvarchar(500), loginName nvarchar(255), ObjectName nvarchar(max), Definition nvarchar(max))
INSERT INTO @PROCESSES
SELECT s.spid, BlockingSPID = s.blocked, DatabaseName = DB_NAME(s.dbid),
s.program_name, s.loginame, ObjectName = OBJECT_NAME(objectid,s.dbid),
Definition = CAST(text AS VARCHAR(MAX))
FROM sys.sysprocesses s
CROSS APPLY
sys.dm_exec_sql_text (sql_handle)
WHERE s.spid > 50 AND
1 = CASE
WHEN @DatabaseName IS NULL AND s.dbid = db_id() THEN 1
WHEN @DatabaseName = 'ALL' THEN 1
WHEN COALESCE(@DatabaseName,'')<>'' AND DB_NAME(s.dbid) LIKE @DatabaseName  + '%' THEN 1
END


;WITH Blocking(SPID, BlockingSPID, DatabaseName, BlockingStatement, RowNo, LevelRow)
AS
(
SELECT s.SPID, s.BlockingSPID, s.DatabaseName, s.Definition,
ROW_NUMBER() OVER(ORDER BY s.SPID),
0 AS LevelRow
FROM @PROCESSES s
JOIN @PROCESSES s1 ON s.SPID = s1.BlockingSPID
WHERE s.BlockingSPID = 0
UNION ALL
SELECT r.SPID,  r.BlockingSPID, r.DatabaseName, r.Definition,
d.RowNo,
d.LevelRow + 1
FROM @PROCESSES r
JOIN Blocking d ON r.BlockingSPID = d.SPID
WHERE r.BlockingSPID > 0
)
SELECT * FROM Blocking
ORDER BY RowNo, LevelRow

Write your own script compressor

Compression Techniques

I have just finished writing my own script compressor to handle the compression on one of my larger systems. You may ask why I didn't just use one of the existing free compressors out there like jsmin or YUI compressor. Well the answer is two fold:

1. I like to write my own code for the simple reason I learn more about my craft doing it this way and although it takes time and usually blood sweat and tears I always come out the other side with more knowledge about development practises in general. See this link about whether to use a framework or write your own for more details.

2. The existing compression tools didn't do all I wanted them to do and also I found certain issues with certain syntax such as complex regular expression literals and conditional comments.

This article is just an overview of some of the things I discovered during the building of my script in case other people want to write their own.

The main features of my compressor are:

• Takes a directory as its source and will output all compressed files to a destination folder replicating the structure of the source folder.
  
• Handles multiple file types e.g JS, PHP, ASP, INC, HTML, CSS
  
• A file such as an ASP file that contains in-line JS, HTML, CSS and ASP will have each "section" compressed according to that sections code type.
  
• The usual compression technique of removing comments, excess white space and empty lines is carried out.
  
• JS code is also compressed by having function parameters and local variables "minified" by replacing variable names with one character names. 
  
• Global objects and common functions are also replaced with short versions.
  
• Debug functions are removed.
• JS functions are saved one per line so even the compressed file is nicely formatted.
• Adds missing terminators ; to aid compression of functions to one line.
• Corrects HTML so that its XHTML valid.
• Skips files that are already compressed.
• Creates a log file detailing the files compressed and the compression rate.

Building a Compressor

I found out during this task that getting a fully working Javascript compressor without the aid of a Java engine is not as simple as it may at first sound. Especially if you wanted like I did each function to appear on its own line and you are handling code that may not be correctly formatted in the first place (e.g missing terminators ;). 

If you want to just remove excess white space and comments then that's fine but doing a "minifier" that renames variables with single letter names is a bit trickier as you need to identify all your functions and parameters correctly for this to work. Remember there are a multitude of ways of defining functions in JavaScript as well so its not just a case of looking for the word function e.g:

function myFunc(var1, var2){ return }

var myFunc = function(var1, var2){ return }

SomeObject.prototype.myFunc = function(var1, var2){ return }

myFunc : function(var1, var2)

(function(){  code }())

Also unless you create a global system that checks which JavaScript functions are being referenced by each file then you can only really minify local function variables and parameters. Otherwise you may change the name of a variable that is being referenced by a file you don't know about causing an error.

If you want to create a very simple minification process you can concentrate on some common global objects such as the window, document and navigator objects. You can also create yourself a small function for document.getElementById and then update all references to that e.g

var _w=window,_d=document,_n=navigator;

//create wrapper function
_g = function(i){
 return _d.getElementById(i);
}

So for every time your site references document.getElementById which is probably quite a lot you have saved yourself 18 characters. Add to that the common use of window and document you will save a fair few bytes just by these changes alone.

Store and Replace

I found the best approach was a layered approach to parsing each file as files such as PHP or ASP will contain a mixture of both server side and client side script as well as HTML and maybe CSS defined in style tags. With the help of some good regular expressions I would look for each type of code using their identifying markers for example look for the open and close style tags. I would then store each block of code in an array, parse it accordingly and then when rebuilding the compressed file re-insert in order. This got round issues where you have ASP script inside in-line JS script blocks within HTML inside an ASP page. Each section would have its own function that compressed according to that languages syntax but all would first store any string and regular expression literals in another array so that they stayed unaffected during any compression as you don't want to be removing white space and changing symbols within string literals.

Fun with regular expressions

Most of my compression was carried out using regular expressions but some tasks such as identifying literals and comments were done in loops. This is pretty easy when your looking for string literals as you know they are going to be enclosed within double or single quotes and you can combine this with a check for single and multi line comments at the same time. However in JS regular expressions can also be defined as literals such as

var re = /^\S\s+[^/].*?>/gi

You cannot just start at the first / and then stop at the next unescaped / as you can use unescaped slashes within character groups e.g [/] so you would end prematurely. You also cannot stop at the last / you come across as you may have multiple statements on the same line such as:

var re = /^\S\s+[^/].*?>/gi, str = str.replace(/##BR##/gi,"<br />");

Plus as you can see the replacement value on the second statement has a forward slash inside it so you would cut off half the replacement value causing a syntax error. I first took the decision that so what a bit more than I intend gets stored as a literal until its put back in but if that extra bit of code also contains variable names that you want to minify you will run into problems.

I got round this problem by first using a regular expression to identify unescaped forward slashes within expressions and replacing them with a placeholder. I could then use another pattern to match string functions such as replace, match, search, split, compile and another for literals and regular expression functions such as test and exec. Once the literal is stored I can put the escaped characters back.

Negative Matches

I also found that the previous technique of using a placeholder value before carrying out a regular expression match was very useful when dealing with complex negative matches. If you have a long string of text and you are trying to carry out a replacement except in a certain instances then this is a good way of having to avoid a complex negative pattern match. For example in my JS compression function I add in extra terminators to the end of lines to make sure I can get a whole function on to the same line. However doing  this sometimes causes issues when terminators are put in places they shouldn't be so at the end I run some corrections which remove terminators from places they shouldn't be such as inside certain brackets. However there are cases where a terminator can appear inside an open bracket legitimately such as a for expression without all the sections. Therefore instead of using a complex negative match to do the excess terminator replacement I use a placeholder e.g

// put a placeholder in for the terminator I want to keep
strJSCompressed = strJSCompressed.replace(/for(;/,"##_FOR_TERM_##");

// carry out the replacement of terminators
strJSCompressed = strJSCompressed.replace(/([\{\(\[,><\|&])(;)/,"$1"); 

Then once the replacements have been carried I put back in all the original values that the placeholders were storing e.g

// put the placeholder back in to my code
strJSCompressed = strJSCompressed.replace(/##_FOR_TERM_##/,"for(;/");

This is a very useful technique when you want to avoid complex regular expressions that involve negative matches as you should know by now complex patterns and long strings combine to cause high CPU!

Another good example is HTML comments. I want to strip all HTML comments apart from the following derivatives:

Server Side Includes e.g <!-- #virtual="/somefile.inc"-->

IE Conditional Comments e.g <!--[if lt IE 7]> OR <![endif]--> 

Server Side META Includes e.g <!--METADATA TYPE="typelib" Blah -->

As you can see trying to write one regular expression that would handle multiple pattern matches within a file that strips all HTML comments apart from those that start with # [ or METADATA would involve some hardcore matching. Its very easy though to match each individual comment type first and replace it with a placeholder, then do my replace for everything between <!-- AND --> and then put the placeholder values back in.

A tidy page is a godly page

As well as carrying all the usual compression functions I also incorporated a number of replacements to tidy up the code. If your going to loop through each page in a system then this seems like a good place to do such things as:

• Make my HTML XHTML compliant by encoding characters, expanding attributes, making sure all attributes are quoted and that my tags are lower case and some other HTML related tweaks.
  
• Removing comments from within SCRIPT blocks as they are not required anymore as well as shortening SCRIPT tags down to the minimum e.g remove the language and type attributes. Obviously this breaks your XHTML compliance but then again you can't have everything.
  
• Combine multi-line string literals together into one variable.
  
• Combine variable declarations (server and client side) into one declaration.
  
• Remove certain function calls such as calls to my custom ShowDebug function that outputs messages for client and server side script. I always build my codebase with the debug statements built in rather than add them in later as it makes debugging quicker and easier. However on a production system these function calls are expensive and unnecessary and should be removed.
  
• Remove excess white space, usually TABS within dynamic SQL strings. Obviously I don't do UPDATES or DELETES only SELECTS but I usually format my code with TABS.

Why Compress Server-Side Code?

Well yes I know that even interpreted languages such as ASP gets compiled into a token based language which is cached by the web server so there is not much scope for compression but the smaller I can make the file size then the better in terms of storage and maybe caching. Plus the main point of the server-side compression was to remove all my ShowDebug function calls to aid performance.

So can I get a copy?

Not at the moment as I am in the process of testing it on a live system to iron out any bugs. At the moment the code is a script that I point at a directory and run. I am hoping to make a C# based windows application version of it and then I might put a copy up on the site.

Should I use a framework?

When to use a framework and when to write your own code

I am always asked at work why I don't just use a framework such as jQuery, prototype, YUI, MooTools etc rather than spend time writing my own code and its a fair point. I have spent time looking at the major frameworks and its all good code written by clever people and if you haven't got the time to spend then I would definitely recommend using a library. Then again if John Reisig had thought like that then millions of people would be using YUI instead of jQuery and Microsoft would be packaging another library with Visual Studio to handle selectors instead.

Libraries are good for many reasons they hide browser incompatibilities from the developer and its good for a team of developers to stick to a standard code base rather than all adding their own functions and bloating a site up with several versions of the same addEvent or toggleClass function.

The downside is that most libraries will contain lots of code that is never even used by the developer. If you're not even going to be using selectors to return DOM objects in your JavaScript and are just looking for a shorter version of document.getElementById then using $('#blah') is not the way to go. 

The other good thing about writing your own code is that you get to understand the language of your trade a whole lot better than if you just relied on a library. There is no better way in my opinion for learning anything that being thrown in at the deep end and having to sink or swim so to speak. Yes it takes much longer as you will have to read up about the early browser wars and compatibility issues, learn about objects and their properties and understand event models and script syntax but it will make you a much better programmer and when bugs appear due to a new version of Internet Explorer you won't have to wait for an update to your framework to be released.

As with all things its swings and roundabouts and just because I like to write my own code and know why things work the way they do does not mean I won't use a library. However having spent the time researching the language for my own code has given me invaluable knowledge and it helps being able to step through something like jQuery and actually understand what its doing and why rather than just knowing that it works.

Problems with Firebug and raised errors

Firebug raising false errors or incorrect line numbers

I have noticed recently that Firebug seems to be giving me unhelpful error reports and it seems to be happening more and more. By unhelpful I mean in the way Internet Explorer used to when an error was raised with an invalid or incorrect line number. I always thought Firebug was pretty spot on for error reporting but it seems that within the last month or so I have been getting quite a lot of errors in the console that say the problem is in file X and on line 120 but in fact after stepping through the problem the problem is actually in file Z and on line 45. Sometimes the error details that are reported in the console do not correspond exactly to those in the standard error console and a lot of the time errors that appear in Firebugs console do not appear in the standard error console.

Possible Causes to spurious error messages

Conflict with Firefox Add-Ons

I have found problems in the past with certain Firefox add-ons that raise errors constantly or intermittently. One such add-on is the user-agent switcher which always raises a 

UserAgentButton is null error and another add on which is a brilliant add-on for Search Engine Optimisation called the SEO Toolbar keeps raising the following error s4fToolbar_cache is undefined.

Both of these errors disappear once the add-on has been disabled or in the case of the SEO toolbar you can turn it off without having to restart your browser. I have quite a number of add-ons on my work PC and due to my experience of errors related to add-ons I wouldn't rule out some sort of clash that is generating incorrect error details. 

Syntax Problems

I have found that sometimes when there are compilation errors usually due to missing or incorrect brackets then the error can be reported incorrectly. If a function hasn't been closed correctly due to a missing bracket then the calling function can sometimes be identified as the erroring function. However a large number of the errors I am getting invalid details for do not meet this criteria.

Firefox or Firebug installations

Within the last couple of months I have had upgrades of both Firefox and Firebug so it maybe that some problem within the application is causing the invalid error details.

If anyone else has found similar issues recently with their Firebug installation it would be good to hear about it. As my colleagues also use Firefox and Firebug but without the various add-ons I have installed do not have these problems it means at the moment I am of the opinion the problem is most likely due to some sort of clash between add-ons as I cannot see such a problem not being spotted and resolved before any upgraded version of Firebug being released. I came to expect this sort of behaviour from IE and it was just understood by everyone that you couldn't get a proper error message when you needed one so its a tad annoying to say the least for me to start experiencing this issue with Firefox.

Problems Upgrading to IE 8

Upgrading to Internet Explorer 8.0

There are plenty of sites already out there listing all the many bugs or "features" that IE 8 has brought to the table but so far the two main ones I have come across are:


Problems when FirebugLite is also running in IE 8.

I was getting a "Function Expected" error on line 1499 in the IsArray function. As a workaround I added the following line as the first line in the function e.g

IsArray:function(_object){
if(!_object) return false;

This prevents the error but the Firebug-lite console does not display correctly in IE 8 when the document mode is also IE 8. To get round this I set the document mode to IE 7 and then it works fine.

Remember IE 8 now has a console in the developer tools options for outputting custom debug messages plus its now got a great debugger tool with all the same features as Firebug so Firebug-Lite isn't really needed anymore. However it should still be possible to run the two side by side.


Issue with clip and rect function

I also found an "invalid argument" error when setting the clip properties using the rect function. The code was for a scroller and the original version that raised the error was:

this.canvas.style.clip = "rect(0 " + this.canvasWidth + " " + this.canvasHeight + " 0)";

The fix was to add "px" after the dimension values and separate the values with commas e.g

this.canvas.style.clip = "rect(0px, " + parseInt(this.canvasWidth) + "px, " + parseInt(this.canvasHeight) + "px, 0px)";

I have come across a few errors such as "null is null or not an object" (you don't say!) which have been simple fixes and have just required testing the values correctly before using them.

I am sure there are hundreds more errors and that many many hours will be devoted to fixing them all in a similar manner to the last 2 major releases of IE. However overall I am very happy that they seem to have caught up with Firefox and the others and have implemented a pretty decent developer tools section including a great debugger that actually gives you a useful error message for once. Plus I like the fact that the GUI hasn't changed very much in the way that IE 6 to IE 7 did and I do like the little touches like the accelerators.

However its a shame that with such a major release they couldn't have gone the whole hog and sorted their Javascript engine out to make that standards compliant as well as the CSS. Apparently they have rewritten the whole JS engine so now was as good a time as any to bite the bullet and do it and they would have made the whole web development community very happy if they had done so. Even with the rewrite their event model is still pretty shoddy and even if they wanted to keep with their intermediary event model (attachEvent, removeEvent, returnValue, srcElement etc) then they could have fixed those annoying little issues that people have spent thousands of development hours resolving such as the this keyword referring to the window and not the object in question and attaching event listeners in order rather than randomly.

It seems pretty likely that more and more companies will get to the point where developing for IE becomes too much work and stop supporting it. Market share of Firefox, Chrome, Safari and Opera are increasing all the time so it may not be that long until you find a lot of sites just redirecting to a Mozilla download page when you access their site in IE. If that does happen then it might be a shame to some people but Microsoft will only have themselves to blame and may find that they have missed a great opportunity with this release to prevent that from occurring.

Detecting IE 8 Compatibility Modes with Javascript

Using Javascript to determine a users browser settings in IE 8

Microsoft's new version of Internet Explorer, IE 8 comes with two configuration settings that allow the user to control the rendering mode and the browser mode so that in fact IE 8 comes with 6 different settings that can drastically alter the behaviour of the browser. See this article about the different settings for an overview.

If you want to be able to determine client side what configuration mix is currently enabled for the browser you can use the following function I have written which will output a little object with the relevant details. Either use it by itself or incorporate it into a fuller browser detection object such as my browser object.

If you are running IE 8 you will see below the output from the function:


download the script here: IE 8 compatibility mode detection script

How to detect which settings the user has enabled in IE 8?

To determine the browser mode you can test the user-agent which will mention Trident/4.0 for IE 8, and IE 8 in compatibility mode. IE 8 running as IE 7 will not mention this so combining this with a check for document.documentMode which is only available in IE 8 will enable you tell if the user has IE 7 or is running IE 8 as IE 7.

To determine the document mode you can test the new property which is available in IE 8 document.documentMode which will return the rendering mode its currently set to e.g 8, 7 or 5 (for quirks mode). Combining this with a check for document.compatMode for previous IE versions lets us determine the rendering engine settings.

IE 8 Document and Browser modes

Controlling IE 8 Browser and Document Modes

In Internet Explorer 8 the developer toolbar can control the following settings and will override any other settings that have been set e.g META tags or the Compatibility View options. On changing a setting the browser will refresh and load the appropriate new configuration.

I will list out the various document and browser modes with the basic differences but if you are in a hurry and just require a Javascript function that you can use to determine the clients current IE8 settings then that link will sort that for you. For an explanation on browser compatibility mode testing then this link will give you an article explaining the combination of agent sniffing and object detection that is required for identifying a clients IE8 browser settings.

Browser Modes:

Internet Explorer 8 Mode

The browser will run as IE 8.0 and the user-agent will appear as an IE 8.0 user-agent e.g

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; GTB5; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 1.1.4322; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022)

Notice the mention of Trident/4.0 which is the name and version of the rendering engine.

A new Javascript engine is used in IE 8.0 so there will be numerous differences for example using getElementById to return an element by name will not work anymore which is the correct way of doing things however if you didn't know this and did use it in IE to access elements you will experience errors when running in full IE 8 mode.

Internet Explorer 7 Mode

The browser will run as if it were actually IE 7.0 and the user-agent will appear as an IE 7.0 user-agent e.g:

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; GTB5; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 1.1.4322; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022)

Javascript will run as it does in IE 7.0 for example using getElementById to return an element by name will work.

Internet Explorer 8 Compatibility Mode

This mode means that, and I quote from ieblog

"In a nutshell, Compatibility View allows content designed for older web browsers to still work well in Internet Explorer 8."

So in all respects the browser is still running as IE 8.0 but allows sites that worked perfectly well in IE 7.0 to continue to work correctly without having to revert to IE 7.0 mode.

By default IE will set all publicly accessible Internet sites to run in IE 8 mode and all Intranet sites to IE 8 compat mode.

For Internet sites it comes across which it feels should run in compatibility mode such as those with strict doctypes then it will display a button to the user to allow them to change to compatibility mode. For sites that are using quirks mode it will not offer this option so do not expect the button to appear all the time.

The user-agent in IE 8 Compatibility Mode is displayed similarly to IE 8 but with a 7 e.g

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; GTB5; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 1.1.4322; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022)

Javascript should run as it did in IE 7 for example using getElementById to return an element by name will work.

Document Modes:

Quirks Mode (e.g IE 5)

This document mode setting will render pages as if there was no doctype specified. This will be the same as if you were using older IE versions such as IE 5.0.

Internet Explorer 7 Standards Mode

This document mode will render pages as they would be displayed in IE 7.0 when a strict doctype was specified.

Internet Explorer 8 Standards Mode (Page Default)

This document mode will render pages in the new IE 8 standards compliant manner. IE 8 apparently adheres to the CSS 2.1 specification and there are numerous changes to be aware of. For instance there is no longer any support for CSS expressions.

For a list of the various changes and potential problems that IE 8 will bring to your development view the following article: http://blogs.msdn.com/ie/archive/2009/03/12/site-compatibility-and-ie8.aspx


How to detect which settings are enabled

If for whatever reason you need to detect client side which of these various settings the user currently has enabled in their browser then you can use a combination of user-agent sniffing and object detection to work out the true browser version and rendering engine. See the following article about how to detect the settings using Javascript.

The new META UA-Compatible tag

Another new feature in IE 8 is the ability to quickly fix any potential problems that all these new document and browser modes may bring by adding a META tag to your existing sites. To force a page to run in IE 8 standards mode we can add the following META tag to pages:

<meta http-equiv="X-UA-Compatible" content="IE=8">

Or if you find that your sites do not currently work in IE 8.0 standards mode you can force them to work as they did in IE 7.0 with the following META tag:

<meta http-equiv="X-UA-Compatible" content="IE=7">

Once you get your site up to scratch you can remove the tags.