What is the practical used of nolock in sql server -


i going around document in msdn , said "no shared locks issued prevent other transactions modifying data read current transaction".

so in lay man term(i.e mine) cause problem of dirty read. dangerous, if why used it?

does knows practical scenario used.

in our case (previous job) used getting ballpark numbers. example table holds millions of e-mails sent in given day, if @ 5:00 want see "where are" can say:

select count(*) dbo.messagetable (nolock)   campaignid = x , customerid = y;

a lot of people suggest using count(*) no where clause. argue if you're willing accept inaccuracy in count(*) may do:

select sum(rows) sys.partitions   [object_id] = object_id('dbo.tablename')   , index_id in (0,1);

this number inaccurate due in-flight transactions, doesn't have scan table, far more efficient. our case use subsets: filtered index in place (for other purposes) query sys.partitions use index_id of filtered index.

in cases, though, using nolock may feel turbo button, inaccuracy may cause worth it. unless system heavily tempdb-bound, should consider read_committed_snapshot current nolock scenarios instead. see pros , cons of read_committed_snapshot


Comments

Post a Comment

Popular posts from this blog

java - Play! framework 2.0: How to display multiple image? -

i need display gallery of photos. here template: @(photos: list[photo]) @title = { <bold>gallery</bold> } @main(title,"photo"){ <ul class="thumbnails"> @for(photo <- photos) { <li class="span3"> <a href="#" class="thumbnail"> <img src="@photo.path" alt=""> </a> </li> } </ul> } and here controller method: public static result getphotos() { return ok(views.html.photo.gallery.render(photo.get())); } and here photo bean : @entity public class photo extends model { @id public long id; @required public string label; public string path; public photo(string path, string label) { this.path = path; this.label = label; } private static finder<long, photo> find = new finder<long, photo>( long.class, photo.class); public static list<phot...
Read more

gmail - Is there any documentation for read-only access to the Google Contacts API? -

i want read-only access user's google contacts. there stackoverflow member wanted this, , received following answer : yes, there is, use https://www.googleapis.com/auth/contacts.readonly scope , "view contacts". this exchange reference read-only access google contacts can find using google. simply using access token obtained attempt read usual google contacts api (i.e. https://www.google.com/m8/feeds ) fails insufficient permissions. similarly, using google contacts api on new target fails 404 errors (for example https://www.googleapis.com/auth/contacts.readonly/default/full ). is there documentation anywhere on how use api, or permissible way access google contacts api full read-write access?
Read more

php - Controller/JToolBar not working in Joomla 2.5 -

relevant code: jtoolbarhelper::custom('savecategories', 'save', '', 'save', false, false); ... <input type="hidden" name="controller" value="easyblogcontroller"> according can dig docs , own previous questions, should call savecategories() function in easyblogcontroller . i've tried setting value easyblog , easyblog.php (file name) current easyblogcontroller (class name). clicking on save button refreshes page. not redirect, echo or var_dump test code put in savecategories() function. var_dump ing jrequest::getvar('controller') , 'task' return correct values. creating controller object , using $controller->execute('task'); works. the values going depend on location of controller trying call, , have couple options here. typically there controller in base folder of component (likely components/com_easyblog) in file called controller.php , class name inside ...
Read more