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  • How does Apache process several requests at a time?

    - by Vicenç Gascó
    In a short question: If 10 requests hit Apache, does it process them one by one, so when R3 finishes, then it starts to run R4, or does it fire 10 processes/threads/whatever and are resolved simultaneously? Now some background: I have a PHP script that takes up to two minutes to do some processes. My question is: while a client is waiting for this 2 minutes, all the other clients requests are being processed? Or also waiting for this one to end? By the way, if there are simultaneous request, how can I handle them? Let's say put a limit on them. Or a limit on resources consumed. For instance I want the server to use its 80% performance on serving the webapp, and just a 20% for those long operations ... because I have no hurry to end them. Doesn't know if it cares but is all in PHP. Thanks in advance!!

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  • Windows 7 won't recognize my second hard drive after reinstall

    - by Shadur
    I recently suffered a total hardware crash on my windows C: drive. Fortunately, I had a spare disk on hand and set about reinstalling. For some reason, during the install it decided to declare my second windows drive as the booting drive, but once the installation was completed it completely and utterly refuses to acknowledge the filesystem -- I'm not even seeing a drive letter, while it /does/ find the linux partitions on the other two drives (even if it can't read any of them). My first (and most important) question: How can I get windows to re-acknowledge the drive, preferably without losing all the data on it? My second question: How can I tell windows to set up its boot loader on the new C: drive?

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  • In terms of load handling, which is better: one server or two of equivalent power?

    - by seldary
    My goal is to figure out if i'm better off with one strong server, or multiple weaker servers with a load balancer. Does the fact of splitting the load between servers have an effect on the total load my website could take? It's hard to single that out, because there are of course a lot of parameters that affect the results, so some assumptions: Putting failover considerations aside - I know it matters, but for the sake of the question's simplicity, lets assume nothing fails. The servers in the multiple servers option have an accumulated "power" equivalent to the one server option (about the same amount of cores and RAM space). If that is too theoretical, here is a concrete question that could help: Suppose I have several instances of exactly the same server - lets call it S. Suppose that server S can serve a load of up to X calls per time unit. Will two S servers with a load balancer serve 2X calls per time unit? significantly more? significantly less?

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  • Remote Desktop Multi Monitor Connection

    - by user196039
    This question may be a bit unusual but I think it's an interesting angle: Why does a remote desktop connection to my server with all four of my 30 inch (@2560x1600) monitors work, even though the server doesn't have a graphics card installed? I guess the graphics are perhaps not really rendered on the server? What exactly happens there so that this works? Searching for this I mostly found "how to enable multi monitor support" but not an answer to my question yet. Any links/documentation I can read to understand this better? (To get all four monitors working well on my local machine the one graphics card I had wasn't even enough, so I have two graphics cards on the local machine now) The operating systems are Windows 7 home premium and it's a Windows Server 2008 R2.

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  • Apache Connection vs. Request

    - by user101570
    I apologize in advance if this is a basic question, but I am quite confused after reading the Apache documentation and other tutorials. Does a single Apache prefork process serve all HTTP requests for a given client? That's what I thought, but when I reduce maxclients down to a low number, my page load times go to a crawl. This despite the fact I'm the only client on the server in question. This would suggest each process serves a single HTTP request at a time, rather than serving all requests within the TimeOut window. So if a single webpage requires 15 HTTP requests to load fully, do I require 15 prefork Apache processes to optimally serve it?

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  • "Clear Text Credential Access Enabled" field

    - by Dave
    Searching for answers about the "Clear Text Credential Access Enabled" field, I found a question on an oracle forum that was my exactly what I was trying to find out. Thinking that my answer would soon be found, I happily click on the link only to find zero replies. All hope was lost. I am posting the question here, hoping that someone on this site will know the answer. Can somebody please explain the usage of "Clear Text Credential Access Enabled" checkbox under "-Security-Advanced tab for Weblogic 11g? What is the difference if we set or unset this flag? If I dont set this flag I get an exception like "Access to sensitive attribute in clear text is not allowed due to the setting of ClearTextCredentialAccessEnabled attribute in SecurityConfigurationMBean" when I try to set a value for the "Credential" field. But what should be the value for "Credential" field if I dont set the "Clear Text Credential Access Enabled"flag?

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  • How to remove GRUB from dual boot (Debian and Windows XP)

    - by All
    I have a computer witch cannot be boot from CD or USB. I have Debian and Windows XP with dual boot via GRUB. Now I want to uninstall Debian and GRUB and restore the Windows MBR. I can enter boot Debian and Windows OSes, but no boot from CD or USB for recovery. How can I remove GRUb and restore MBR from within Windows XP or Debian? NOTE: I asked this question before, but after accepting the answer, I found that Windows XP does not have fdisk command. However, I think it is too late to continue the discussion there; thus, I asked this brand new question.

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  • Will a `wireless n` network adapter work `wireless g` router?

    - by ShoeLace1291
    I have verizon fios internet service. I believe they use a Wireless G router, but I just have one question. I currently am using a 54mbps wireless pci adapter in my Windows 7 custom build. It drops the internet connection all the time and is starting to get very irritating. I'm thinking about buying a new one, but all the 300mbps cards on newegg are wireless n. So my question is, will a wireless n network adapter make a difference with a wireless g router?

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  • Run SSH trough a proxy

    - by Row Minds
    I have a question. How can i run SSH trough a proxy or a SSH Tunneling Protocol? For example i have a computer(Ubuntu) with ip eg. 123.123.123.123 and i want to connect to my server trough a proxy eg. 111.111.111.111 so i can see in lastlog that the last authentication was made from 123.123.123.123 . I need this because i cannot access a certain server at work only with an specified range IP. What i tried so far was http://daniel.haxx.se/docs/sshproxy.html where i used ssh -D 1 [email protected] -p 443 where i had 127.0.0.1 forwarded to a SSH Tunneling Protocol http://www.nixtutor.com/linux/installing-and-configuring-an-ssh-server/ (i configurated listening on port 443 but no result, still no connection (denied) ...) This question may sound simple, but i can't figure it out, can you please help me? Thanks.

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  • Server Design Enquiry [closed]

    - by Brandon Gelfand
    I am really new to this and am having trouble with how I can store information from a website. I am going to be making a site similar to dropbox for my company and there is gonna be around 40 TB of space that we need to be able to access on the go, for instance pull the file up on the phone or off our laptop using the internet. Obviously using an Amazon S3 server is not the most cost effective way of doing this so how can I make my own server to hold all of the info and communicate to it from a website? Please I need as much help as possible, like a blueprint or something. Thanks and sorry for the noobish question but I can't really find an exact answer to my question.

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  • Mirrored servers in data centers nationwide -- how? [closed]

    - by Sysadmin Evstar
    Possible Duplicate: Mirrored servers in data centers nationwide — how? Mirrored servers in data centers nationwide -- how? I flunked my IT interview by getting this question wrong. I thought that in the various metropolitan areas, an "http://google.com" request goes to the ISP's DNS server, which somehow returns an IP address for one of several geographically-nearby http servers, and then something internally rolls over to the next available local Google server. But then, I could not explain where the table of available local Google servers is actually cached, or the details of the IP address rollover. Or how they could manually take some server out of the rotation, from anywhere. So, what should I be reading now so I can ace this question next time? Also, what daemons run on these machines 24/7 to keep all those mirrored database disks synchronized?

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  • Single ipv6 from /64 subnet

    - by PartyPete
    I have a newb question I'd like to ask. We have an dedicated server and we got an ipv6 /64 block. We want to use squid to make proxy and use those IP. And my question now is: Is it possible to use only one IP out of range? for example: let's say I have a range of IPs ffff:ffff::/64, and want to use only one address from it: ffff:ffff::1/128 or ffff:ffff::2/128 but whenever I set squid like this I always get from 'what is my ip' services whole subnet which is again ffff:ffff::. What I want to achieve is to get from those 'what is my ip' services to send me back IP ffff:ffff::1 (or 2 for that matter) Am I doing something wrong?

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  • Roughly, what percentage of users will reach changed DNS?

    - by user3722246
    If my main server go offline for some reason for +1hrs, I'm planning to make a DNS change so users will access secondary server. It is not a perfect solution to decrease downtime but it is simple and would work. I'm not sure about its usefulness. So I have a question. If I'm going to make a DNS change to an A record for my domain (changing from one IP to another), what percentage of users are moved over to the new info in 2hrs? (roughly) I know this is a vague question and there are lots of variables but any input is welcomed because I had painful downtime experiences and don't want to experience it again. Thanks

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  • Administrators: People interaction and Working hours?

    - by sanksjaya
    Do admins get to meet a lot of new people on a daily basis at work? And what kind of people domain do they interact with? Secondly, I've had this myth for a long time that unlike programmers, Network/System/Security Admins get locked-up in a den and juiced up late nights and early mornings. Most of the time they had to slip out of work without being noticed. How true and often does this happen for you? I understand there is no specific answer to this question as it depends on the type of working organization. But just looking out for answers from your experience. Thanks :) Clarification: I've had the question posted on to stackoverflow and they closed it. So I posted it here.

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  • Windows API Error 2 when installing MikTex (Win7)

    - by GreenAsJade
    I am trying to install MikTex 2.9.3927 on Windows 7 x64. Very early in the installation process, I get a MikTex setup wizard error saying: "Windows API Error 2: The system cannot find the file specified Details: C:...\somefile.tpm" The file that results in the error seems to be different every time I try. I have tried many different installation paths, with many different setup options. The same error occurs if I download the ~138MB "Basic MiKTeX 2.9" Installer or if I use the Net Installer to download the entire setup (~1GB). Note that this is a duplicate question - the other copy of this question is closed to users of under 10 rep. I have asked it so that I can provide an updated answer...

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  • How to run script from root as another user (with user PATH)

    - by Sandra
    I would like to have these commands run as the ss user from root mkdir bin cp -r /opt/gitolite . gitolite/install -ln gitolite setup -pk ss.pub mkdir -p .gitolite/hooks/common ln -s /opt/pre-receive .gitolite/hooks/common/ so everything is executed in /home/ss. The 4th line requires $HOME/bin as you can see from the 3rd line. The only way I can get it to work is by adding su -c "command" ss to each line, which is not a nice hack. This is an extension to my previous question, where I wasn't precise enough. Question How do I run all these commands as a script in a practical way?

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  • Creating a multi-tenant application using PostgreSQL's schemas and Rails

    - by ramon.tayag
    Stuff I've already figured out I'm learning how to create a multi-tenant application in Rails that serves data from different schemas based on what domain or subdomain is used to view the application. I already have a few concerns answered: How can you get subdomain-fu to work with domains as well? Here's someone that asked the same question which leads you to this blog. What database, and how will it be structured? Here's an excellent talk by Guy Naor, and good question about PostgreSQL and schemas. I already know my schemas will all have the same structure. They will differ in the data they hold. So, how can you run migrations for all schemas? Here's an answer. Those three points cover a lot of the general stuff I need to know. However, in the next steps I seem to have many ways of implementing things. I'm hoping that there's a better, easier way. Finally, to my question When a new user signs up, I can easily create the schema. However, what would be the best and easiest way to load the structure that the rest of the schemas already have? Here are some questions/scenarios that might give you a better idea. Should I pass it on to a shell script that dumps the public schema into a temporary one, and imports it back to my main database (pretty much like what Guy Naor says in his video)? Here's a quick summary/script I got from the helpful #postgres on freenode. While this will probably work, I'm gonna have to do a lot of stuff outside of Rails, which makes me a bit uncomfortable.. which also brings me to the next question. Is there a way to do this straight from Ruby on Rails? Like create a PostgreSQL schema, then just load the Rails database schema (schema.rb - I know, it's confusing) into that PostgreSQL schema. Is there a gem/plugin that has these things already? Methods like "create_pg_schema_and_load_rails_schema(the_new_schema_name)". If there's none, I'll probably work at making one, but I'm doubtful about how well tested it'll be with all the moving parts (especially if I end up using a shell script to create and manage new PostgreSQL schemas). Thanks, and I hope that wasn't too long! UPDATE May 11, 2010 11:26 GMT+8 Since last night I've been able to get a method to work that creates a new schema and loads schema.rb into it. Not sure if what I'm doing is correct (seems to work fine, so far) but it's a step closer at least. If there's a better way please let me know. module SchemaUtils def self.add_schema_to_path(schema) conn = ActiveRecord::Base.connection conn.execute "SET search_path TO #{schema}, #{conn.schema_search_path}" end def self.reset_search_path conn = ActiveRecord::Base.connection conn.execute "SET search_path TO #{conn.schema_search_path}" end def self.create_and_migrate_schema(schema_name) conn = ActiveRecord::Base.connection schemas = conn.select_values("select * from pg_namespace where nspname != 'information_schema' AND nspname NOT LIKE 'pg%'") if schemas.include?(schema_name) tables = conn.tables Rails.logger.info "#{schema_name} exists already with these tables #{tables.inspect}" else Rails.logger.info "About to create #{schema_name}" conn.execute "create schema #{schema_name}" end # Save the old search path so we can set it back at the end of this method old_search_path = conn.schema_search_path # Tried to set the search path like in the methods above (from Guy Naor) # conn.execute "SET search_path TO #{schema_name}" # But the connection itself seems to remember the old search path. # If set this way, it works. conn.schema_search_path = schema_name # Directly from databases.rake. # In Rails 2.3.5 databases.rake can be found in railties/lib/tasks/databases.rake file = "#{Rails.root}/db/schema.rb" if File.exists?(file) Rails.logger.info "About to load the schema #{file}" load(file) else abort %{#{file} doesn't exist yet. It's possible that you just ran a migration!} end Rails.logger.info "About to set search path back to #{old_search_path}." conn.schema_search_path = old_search_path end end

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  • How does this decorator make a call to the 'register' method?

    - by BryanWheelock
    I'm trying to understand what is going on in the decorator @not_authenticated. The next step in the TraceRoute is to the method 'register' which is also located in django_authopenid/views.py which I just don't understand because I don't see anywhere that register is even mentioned in signin() How is the method 'register' called? def not_authenticated(func): """ decorator that redirect user to next page if he is already logged.""" def decorated(request, *args, **kwargs): if request.user.is_authenticated(): next = request.GET.get("next", "/") return HttpResponseRedirect(next) return func(request, *args, **kwargs) return decorated @not_authenticated def signin(request,newquestion=False,newanswer=False): """ signin page. It manage the legacy authentification (user/password) and authentification with openid. url: /signin/ template : authopenid/signin.htm """ request.encoding = 'UTF-8' on_failure = signin_failure next = clean_next(request.GET.get('next')) form_signin = OpenidSigninForm(initial={'next':next}) form_auth = OpenidAuthForm(initial={'next':next}) if request.POST: if 'bsignin' in request.POST.keys() or 'openid_username' in request.POST.keys(): form_signin = OpenidSigninForm(request.POST) if form_signin.is_valid(): next = clean_next(form_signin.cleaned_data.get('next')) sreg_req = sreg.SRegRequest(optional=['nickname', 'email']) redirect_to = "%s%s?%s" % ( get_url_host(request), reverse('user_complete_signin'), urllib.urlencode({'next':next}) ) return ask_openid(request, form_signin.cleaned_data['openid_url'], redirect_to, on_failure=signin_failure, sreg_request=sreg_req) elif 'blogin' in request.POST.keys(): # perform normal django authentification form_auth = OpenidAuthForm(request.POST) if form_auth.is_valid(): user_ = form_auth.get_user() login(request, user_) next = clean_next(form_auth.cleaned_data.get('next')) return HttpResponseRedirect(next) question = None if newquestion == True: from forum.models import AnonymousQuestion as AQ session_key = request.session.session_key qlist = AQ.objects.filter(session_key=session_key).order_by('-added_at') if len(qlist) > 0: question = qlist[0] answer = None if newanswer == True: from forum.models import AnonymousAnswer as AA session_key = request.session.session_key alist = AA.objects.filter(session_key=session_key).order_by('-added_at') if len(alist) > 0: answer = alist[0] return render('authopenid/signin.html', { 'question':question, 'answer':answer, 'form1': form_auth, 'form2': form_signin, 'msg': request.GET.get('msg',''), 'sendpw_url': reverse('user_sendpw'), }, context_instance=RequestContext(request)) Looking at the request, it seems that account/register/ does reference the register method with 'PATH_INFO': u'/account/register/' Here is the request: <WSGIRequest GET:<QueryDict: {}>, POST:<QueryDict: {u'username': [u'BryanWheelock'], u'email': [u'[email protected]'], u'bnewaccount': [u'Signup']}>, COOKIES:{'__utma': '127460431.1218630960.1266769637.1266769637.1266864494.2', '__utmb': '127460431.3.10.1266864494', '__utmc': '127460431', '__utmz': '127460431.1266769637.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)', 'sessionid': 'fb15ee538320170a22d3a3a324aad968'}, META:{'CONTENT_LENGTH': '74', 'CONTENT_TYPE': 'application/x-www-form-urlencoded', 'DOCUMENT_ROOT': '/usr/local/apache2/htdocs', 'GATEWAY_INTERFACE': 'CGI/1.1', 'HTTP_ACCEPT': 'application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5', 'HTTP_ACCEPT_CHARSET': 'ISO-8859-1,utf-8;q=0.7,*;q=0.3', 'HTTP_ACCEPT_ENCODING': 'gzip,deflate,sdch', 'HTTP_ACCEPT_LANGUAGE': 'en-US,en;q=0.8', 'HTTP_CACHE_CONTROL': 'max-age=0', 'HTTP_CONNECTION': 'close', 'HTTP_COOKIE': '__utmz=127460431.1266769637.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=127460431.1218630960.1266769637.1266769637.1266864494.2; __utmc=127460431; __utmb=127460431.3.10.1266864494; sessionid=fb15ee538320170a22d3a3a324aad968', 'HTTP_HOST': 'workproject.com', 'HTTP_ORIGIN': 'http://workproject.com', 'HTTP_REFERER': 'http://workproject.com/account/signin/complete/?next=%2F&janrain_nonce=2010-02-22T18%3A49%3A53ZG2KXci&openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0&openid.mode=id_res&openid.op_endpoint=https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2Fud&openid.response_nonce=2010-02-22T18%3A49%3A53Znxxxxxxxxxw&openid.return_to=http%3A%2F%2Fworkproject.com%2Faccount%2Fsignin%2Fcomplete%2F%3Fnext%3D%252F%26janrain_nonce%3D2010-02-22T18%253A49%253A53ZG2KXci&openid.assoc_handle=AOQobUepU4xs-kGg5LiyLzfN3RYv0I0Jocgjf_1odT4RR9zfMFpQVpMg&openid.signed=op_endpoint%2Cclaimed_id%2Cidentity%2Creturn_to%2Cresponse_nonce%2Cassoc_handle&openid.sig=Jf76i2RNhqpLTJMjeQ0nnQz6fgA%3D&openid.identity=https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2Fid%3Fid%3DAItxxxxxxxxxs9CxHQ3PrHw_N5_3j1HM&openid.claimed_id=https%3A%2F%2Fwww.google.com%2Faccounts%2Fo8%2Fid%3Fid%3DAItOaxxxxxxxxxxx4s9CxHQ3PrHw_N5_3j1HM', 'HTTP_USER_AGENT': 'Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_5_8; en-US) AppleWebKit/532.9 (KHTML, like Gecko) Chrome/5.0.307.7 Safari/532.9', 'HTTP_X_FORWARDED_FOR': '96.8.31.235', 'PATH': '/usr/bin:/bin', 'PATH_INFO': u'/account/register/', 'PATH_TRANSLATED': '/home/spirituality/webapps/work/spirit_app.wsgi/account/register/', 'QUERY_STRING': '', 'REMOTE_ADDR': '127.0.0.1', 'REMOTE_PORT': '59956', 'REQUEST_METHOD': 'POST', 'REQUEST_URI': '/account/register/', 'SCRIPT_FILENAME': '/home/spirituality/webapps/spirituality/spirit_app.wsgi', 'SCRIPT_NAME': u'', 'SERVER_ADDR': '127.0.0.1', 'SERVER_ADMIN': '[no address given]', 'SERVER_NAME': 'workproject.com', 'SERVER_PORT': '80', 'SERVER_PROTOCOL': 'HTTP/1.0', 'SERVER_SIGNATURE': '', 'SERVER_SOFTWARE': 'Apache/2.2.12 (Unix) mod_wsgi/2.5 Python/2.5.4', 'mod_wsgi.application_group': 'www.workProject.com|', 'mod_wsgi.callable_object': 'application', 'mod_wsgi.listener_host': '', 'mod_wsgi.listener_port': '25931', 'mod_wsgi.process_group': '', 'mod_wsgi.reload_mechanism': '0', 'mod_wsgi.script_reloading': '1', 'mod_wsgi.version': (2, 5), 'wsgi.errors': <mod_wsgi.Log object at 0xb7ce0038>, 'wsgi.file_wrapper': <built-in method file_wrapper of mod_wsgi.Adapter object at 0xb7e94b18>, 'wsgi.input': <mod_wsgi.Input object at 0x999cc78>, 'wsgi.multiprocess': True, 'wsgi.multithread': False, 'wsgi.run_once': False, 'wsgi.url_scheme': 'http', 'wsgi.version': (1, 0)}>

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  • Slow queries in Rails- not sure if my indexes are being used.

    - by Max Williams
    I'm doing a quite complicated find with lots of includes, which rails is splitting into a sequence of discrete queries rather than do a single big join. The queries are really slow - my dataset isn't massive, with none of the tables having more than a few thousand records. I have indexed all of the fields which are examined in the queries but i'm worried that the indexes aren't helping for some reason: i installed a plugin called "query_reviewer" which looks at the queries used to build a page, and lists problems with them. This states that indexes AREN'T being used, and it features the results of calling 'explain' on the query, which lists various problems. Here's an example find call: Question.paginate(:all, {:page=>1, :include=>[:answers, :quizzes, :subject, {:taggings=>:tag}, {:gradings=>[:age_group, :difficulty]}], :conditions=>["((questions.subject_id = ?) or (questions.subject_id = ? and tags.name = ?))", "1", 19, "English"], :order=>"subjects.name, (gradings.difficulty_id is null), gradings.age_group_id, gradings.difficulty_id", :per_page=>30}) And here are the generated sql queries: SELECT DISTINCT `questions`.id FROM `questions` LEFT OUTER JOIN `taggings` ON `taggings`.taggable_id = `questions`.id AND `taggings`.taggable_type = 'Question' LEFT OUTER JOIN `tags` ON `tags`.id = `taggings`.tag_id LEFT OUTER JOIN `subjects` ON `subjects`.id = `questions`.subject_id LEFT OUTER JOIN `gradings` ON gradings.question_id = questions.id WHERE (((questions.subject_id = '1') or (questions.subject_id = 19 and tags.name = 'English'))) ORDER BY subjects.name, (gradings.difficulty_id is null), gradings.age_group_id, gradings.difficulty_id LIMIT 0, 30 SELECT `questions`.`id` AS t0_r0 <..etc...> FROM `questions` LEFT OUTER JOIN `answers` ON answers.question_id = questions.id LEFT OUTER JOIN `quiz_questions` ON (`questions`.`id` = `quiz_questions`.`question_id`) LEFT OUTER JOIN `quizzes` ON (`quizzes`.`id` = `quiz_questions`.`quiz_id`) LEFT OUTER JOIN `subjects` ON `subjects`.id = `questions`.subject_id LEFT OUTER JOIN `taggings` ON `taggings`.taggable_id = `questions`.id AND `taggings`.taggable_type = 'Question' LEFT OUTER JOIN `tags` ON `tags`.id = `taggings`.tag_id LEFT OUTER JOIN `gradings` ON gradings.question_id = questions.id LEFT OUTER JOIN `age_groups` ON `age_groups`.id = `gradings`.age_group_id LEFT OUTER JOIN `difficulties` ON `difficulties`.id = `gradings`.difficulty_id WHERE (((questions.subject_id = '1') or (questions.subject_id = 19 and tags.name = 'English'))) AND `questions`.id IN (602, 634, 666, 698, 730, 762, 613, 645, 677, 709, 741, 592, 624, 656, 688, 720, 752, 603, 635, 667, 699, 731, 763, 614, 646, 678, 710, 742, 593, 625) ORDER BY subjects.name, (gradings.difficulty_id is null), gradings.age_group_id, gradings.difficulty_id SELECT count(DISTINCT `questions`.id) AS count_all FROM `questions` LEFT OUTER JOIN `answers` ON answers.question_id = questions.id LEFT OUTER JOIN `quiz_questions` ON (`questions`.`id` = `quiz_questions`.`question_id`) LEFT OUTER JOIN `quizzes` ON (`quizzes`.`id` = `quiz_questions`.`quiz_id`) LEFT OUTER JOIN `subjects` ON `subjects`.id = `questions`.subject_id LEFT OUTER JOIN `taggings` ON `taggings`.taggable_id = `questions`.id AND `taggings`.taggable_type = 'Question' LEFT OUTER JOIN `tags` ON `tags`.id = `taggings`.tag_id LEFT OUTER JOIN `gradings` ON gradings.question_id = questions.id LEFT OUTER JOIN `age_groups` ON `age_groups`.id = `gradings`.age_group_id LEFT OUTER JOIN `difficulties` ON `difficulties`.id = `gradings`.difficulty_id WHERE (((questions.subject_id = '1') or (questions.subject_id = 19 and tags.name = 'English'))) Actually, looking at these all nicely formatted here, there's a crazy amount of joining going on here. This can't be optimal surely. Anyway, it looks like i have two questions. 1) I have an index on each of the ids and foreign key fields referred to here. The second of the above queries is the slowest, and calling explain on it (doing it directly in mysql) gives me the following: +----+-------------+----------------+--------+---------------------------------------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+--------+---------------------------------------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------+------+----------------------------------------------+ | 1 | SIMPLE | questions | range | PRIMARY,index_questions_on_subject_id | PRIMARY | 4 | NULL | 30 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | answers | ref | index_answers_on_question_id | index_answers_on_question_id | 5 | millionaire_development.questions.id | 2 | | | 1 | SIMPLE | quiz_questions | ref | index_quiz_questions_on_question_id | index_quiz_questions_on_question_id | 5 | millionaire_development.questions.id | 1 | | | 1 | SIMPLE | quizzes | eq_ref | PRIMARY | PRIMARY | 4 | millionaire_development.quiz_questions.quiz_id | 1 | | | 1 | SIMPLE | subjects | eq_ref | PRIMARY | PRIMARY | 4 | millionaire_development.questions.subject_id | 1 | | | 1 | SIMPLE | taggings | ref | index_taggings_on_taggable_id_and_taggable_type,index_taggings_on_taggable_type | index_taggings_on_taggable_id_and_taggable_type | 263 | millionaire_development.questions.id,const | 1 | | | 1 | SIMPLE | tags | eq_ref | PRIMARY | PRIMARY | 4 | millionaire_development.taggings.tag_id | 1 | Using where | | 1 | SIMPLE | gradings | ref | index_gradings_on_question_id | index_gradings_on_question_id | 5 | millionaire_development.questions.id | 2 | | | 1 | SIMPLE | age_groups | eq_ref | PRIMARY | PRIMARY | 4 | millionaire_development.gradings.age_group_id | 1 | | | 1 | SIMPLE | difficulties | eq_ref | PRIMARY | PRIMARY | 4 | millionaire_development.gradings.difficulty_id | 1 | | +----+-------------+----------------+--------+---------------------------------------------------------------------------------+-------------------------------------------------+---------+------------------------------------------------+------+----------------------------------------------+ The query_reviewer plugin has this to say about it - it lists several problems: Table questions: Using temporary table, Long key length (263), Using filesort MySQL must do an extra pass to find out how to retrieve the rows in sorted order. To resolve the query, MySQL needs to create a temporary table to hold the result. The key used for the index was rather long, potentially affecting indices in memory 2) It looks like rails isn't splitting this find up in a very optimal way. Is it, do you think? Am i better off doing several find queries manually rather than one big combined one? Grateful for any advice, max

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  • how to get the result query one by one in jsp and mysql

    - by user261002
    I am trying to implement as Online Mock exam in JSP, but I have a problem to get the questions one by one, it get connceted for the first time, and show me the first question and answers, but when I click on "next" again, it still show me the first question, I think by clicking on "next" it start querying again. please help me. this is my bean : database.SQLSelectStatement sqlselect; database.SQLSelectStatement sqlselect2; static ResultSet questions; static ResultSetMetaData rsm; static ResultSet answers; public void setConnection() throws SQLException { if (database.DatabaseManager.getInstance().connectionOK()) { sqlselect = new database.SQLSelectStatement("question", "question", "0"); sqlselect2 = new database.SQLSelectStatement("answers", "question_id", "0"); questions = sqlselect.executeWithNoCondition(); } } public int i=0; public String getQuestions() throws SQLException { String result = ""; rsm = questions.getMetaData(); for (int i = 0; i < rsm.getColumnCount(); i++) { result += "<th>" + rsm.getColumnName(i + 1) + "</th>"; } if (!questions.isLast()) { questions.next(); System.out.println(i+1); result += "<tr>"; result += "<td>" + questions.getInt(1) + "</td>"; result += "<td>" + questions.getString(2) + "</td>"; result += "</tr>"; result += "<tr>"; sqlselect2.setValue(String.valueOf(questions.getInt(1))); answers = sqlselect2.Execute(); while (answers.next()) { result += "<tr> <td colspan='2'><input type='radio' name='answer' value='" + answers.getString(2) + "'> " + answers.getString(2) + "</td></tr>"; } result += "</tr>"; answers.close(); } return result; } this is the HTML: <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>JSP Page</title> </head> <body> <h1>JSP Page</h1> <jsp:useBean id="exam" class="exam.ExamQuestions"></jsp:useBean> <% exam.setConnection(); %> <form method="post"> <table > <%=exam.getQuestions()%> </table> <input type="submit" name="action" value="next"/> </form> <% String action = request.getParameter("action"); if ("next".equals(action)) { out.println(request.getParameter("answer")); } %> </body> </html>

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  • Round-twice error in .NET's Double.ToString method

    - by Jeppe Stig Nielsen
    Mathematically, consider for this question the rational number 8725724278030350 / 2**48 where ** in the denominator denotes exponentiation, i.e. the denominator is 2 to the 48th power. (The fraction is not in lowest terms, reducible by 2.) This number is exactly representable as a System.Double. Its decimal expansion is 31.0000000000000'49'73799150320701301097869873046875 (exact) where the apostrophes do not represent missing digits but merely mark the boudaries where rounding to 15 resp. 17 digits is to be performed. Note the following: If this number is rounded to 15 digits, the result will be 31 (followed by thirteen 0s) because the next digits (49...) begin with a 4 (meaning round down). But if the number is first rounded to 17 digits and then rounded to 15 digits, the result could be 31.0000000000001. This is because the first rounding rounds up by increasing the 49... digits to 50 (terminates) (next digits were 73...), and the second rounding might then round up again (when the midpoint-rounding rule says "round away from zero"). (There are many more numbers with the above characteristics, of course.) Now, it turns out that .NET's standard string representation of this number is "31.0000000000001". The question: Isn't this a bug? By standard string representation we mean the String produced by the parameterles Double.ToString() instance method which is of course identical to what is produced by ToString("G"). An interesting thing to note is that if you cast the above number to System.Decimal then you get a decimal that is 31 exactly! See this Stack Overflow question for a discussion of the surprising fact that casting a Double to Decimal involves first rounding to 15 digits. This means that casting to Decimal makes a correct round to 15 digits, whereas calling ToSting() makes an incorrect one. To sum up, we have a floating-point number that, when output to the user, is 31.0000000000001, but when converted to Decimal (where 29 digits are available), becomes 31 exactly. This is unfortunate. Here's some C# code for you to verify the problem: static void Main() { const double evil = 31.0000000000000497; string exactString = DoubleConverter.ToExactString(evil); // Jon Skeet, http://csharpindepth.com/Articles/General/FloatingPoint.aspx Console.WriteLine("Exact value (Jon Skeet): {0}", exactString); // writes 31.00000000000004973799150320701301097869873046875 Console.WriteLine("General format (G): {0}", evil); // writes 31.0000000000001 Console.WriteLine("Round-trip format (R): {0:R}", evil); // writes 31.00000000000005 Console.WriteLine(); Console.WriteLine("Binary repr.: {0}", String.Join(", ", BitConverter.GetBytes(evil).Select(b => "0x" + b.ToString("X2")))); Console.WriteLine(); decimal converted = (decimal)evil; Console.WriteLine("Decimal version: {0}", converted); // writes 31 decimal preciseDecimal = decimal.Parse(exactString, CultureInfo.InvariantCulture); Console.WriteLine("Better decimal: {0}", preciseDecimal); // writes 31.000000000000049737991503207 } The above code uses Skeet's ToExactString method. If you don't want to use his stuff (can be found through the URL), just delete the code lines above dependent on exactString. You can still see how the Double in question (evil) is rounded and cast.

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  • Get mutually and non mutually existening Fields in same table in Two columns

    - by ranabra
    This is a question similar to another question I posted here but is a little different. I am trying to get a list of all instances of mutual and non-mutual existing Users. What I mean is that the returned result from the query will return a list of users along with their co-worker. It is similar to the question here, but the difference is that non mutual users will be returned too and with out the "duplicity" mutually existing users return in the list (See image below in-order simplify it all). I took the original answer from Thomas (Thanx again Thomas) Select D1.u_username, U1.Permission, U1.Grade, D1.f_username, U2.Permission, U2.Gradefrom tblDynamicUserList As D1    Join tblDynamicUserList As D2        On D2.u_username = D1.f_username            And D2.f_username = D1.u_username    Join tblUsers As U1        On U1.u_username = D1.u_username    Join tblUsers As U2        On U2.u_username = D2.u_username and after some several trials I commented out 2 lines (Below). The returned result are exactly as described in the beginning of this question, but with the "duplicity" returned by mutually existing users in the table. How can I eliminate this duplicity? Select D1.u_username, U1.Permission, U1.Grade, D1.f_username, U2.Permission, U2.Gradefrom tblDynamicUserList As D1    Join tblDynamicUserList As D2        On D2.u_username = D1.f_username            /* And D2.f_username = D1.u_username */    Join tblUsers As U1        On U1.u_username = D1.u_username    Join tblUsers As U2        On U2.u_username = D2.u_username /* WHERE D1.U_userName < D1.f_username */ *Screenshot that hopefully helps explain it all. Database is SQL 2005. Many thanx in advance

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  • Is there a way to delay compilation of a stored procedure's execution plan?

    - by Ian Henry
    (At first glance this may look like a duplicate of http://stackoverflow.com/questions/421275 or http://stackoverflow.com/questions/414336, but my actual question is a bit different) Alright, this one's had me stumped for a few hours. My example here is ridiculously abstracted, so I doubt it will be possible to recreate locally, but it provides context for my question (Also, I'm running SQL Server 2005). I have a stored procedure with basically two steps, constructing a temp table, populating it with very few rows, and then querying a very large table joining against that temp table. It has multiple parameters, but the most relevant is a datetime "@MinDate." Essentially: create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @MinDate If I just execute this as a normal query, by declaring @MinDate as a local variable and running that, it produces an optimal execution plan that executes very quickly (first joins on #smallTable and then only considers a very small subset of rows from aGiantTable while doing other operations). It seems to realize that #smallTable is tiny, so it would be efficient to start with it. This is good. However, if I make that a stored procedure with @MinDate as a parameter, it produces a completely inefficient execution plan. (I am recompiling it each time, so it's not a bad cached plan...at least, I sure hope it's not) But here's where it gets weird. If I change the proc to the following: declare @LocalMinDate datetime set @LocalMinDate = @MinDate --where @MinDate is still a parameter create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @LocalMinDate Then it gives me the efficient plan! So my theory is this: when executing as a plain query (not as a stored procedure), it waits to construct the execution plan for the expensive query until the last minute, so the query optimizer knows that #smallTable is small and uses that information to give the efficient plan. But when executing as a stored procedure, it creates the entire execution plan at once, thus it can't use this bit of information to optimize the plan. But why does using the locally declared variables change this? Why does that delay the creation of the execution plan? Is that actually what's happening? If so, is there a way to force delayed compilation (if that indeed is what's going on here) even when not using local variables in this way? More generally, does anyone have sources on when the execution plan is created for each step of a stored procedure? Googling hasn't provided any helpful information, but I don't think I'm looking for the right thing. Or is my theory just completely unfounded? Edit: Since posting, I've learned of parameter sniffing, and I assume this is what's causing the execution plan to compile prematurely (unless stored procedures indeed compile all at once), so my question remains -- can you force the delay? Or disable the sniffing entirely? The question is academic, since I can force a more efficient plan by replacing the select * from aGiantTable with select * from (select * from aGiantTable where ID in (select ID from #smallTable)) as aGiantTable Or just sucking it up and masking the parameters, but still, this inconsistency has me pretty curious.

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  • Android Alert Dialog Extract User Choice Radio Button?

    - by kel196
    Apologies for any coding ignorance, I am a beginner and am still learning! I am creating a quiz app which reads questions off a SQL database and plots them as points on a google map. As the user clicks each point, an alert dialog appears with radio buttons to answer some question. My radiobuttons are in CustomItemizedOverlay file and when I click submit, I want to be able to send the user choice back to the database, save it and return to the user if their answer is correct. My question is this, how do I pass the user choice out once the submit button has been clicked? I tried making a global variable to read what was selected to no avail. Any suggestions would be appreciated! If I need to post any other code, please ask and I will do so ASAP! package uk.ac.ucl.cege.cegeg077.uceskkw; import java.util.ArrayList; import android.app.AlertDialog; import android.content.Context; import android.content.DialogInterface; import android.graphics.drawable.Drawable; import android.widget.Toast; import com.google.android.maps.ItemizedOverlay; import com.google.android.maps.OverlayItem; public class CustomItemizedOverlay2 extends ItemizedOverlay<OverlayItem> { private ArrayList<OverlayItem> mapOverlays = new ArrayList<OverlayItem>(); private Context context; public CustomItemizedOverlay2(Drawable defaultMarker) { super(boundCenterBottom(defaultMarker)); } public CustomItemizedOverlay2(Drawable defaultMarker, Context context) { this(defaultMarker); this.context = context; } @Override protected OverlayItem createItem(int i) { return mapOverlays.get(i); } @Override public int size() { return mapOverlays.size(); } @Override protected boolean onTap(int index) { OverlayItem item = mapOverlays.get(index); // gets the snippet from ParseKMLAndDisplayOnMap and splits it back into // a string. final CharSequence allanswers[] = item.getSnippet().split("::"); AlertDialog.Builder dialog = new AlertDialog.Builder(context); dialog.setIcon(R.drawable.easterbunnyegg); dialog.setTitle(item.getTitle()); dialog.setSingleChoiceItems(allanswers, -1, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(context, "You have selected " + allanswers[whichButton], Toast.LENGTH_SHORT).show(); } }); dialog.setPositiveButton(R.string.button_submit, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { dialog.dismiss(); // int selectedPosition = ((AlertDialog) // dialog).getListView().getCheckedItemPosition(); Toast.makeText(context, "hi!", Toast.LENGTH_SHORT) .show(); } }); dialog.setNegativeButton(R.string.button_close, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { dialog.dismiss(); // on cancel button action } }); AlertDialog question = dialog.create(); question.show(); return true; } public void addOverlay(OverlayItem overlay) { mapOverlays.add(overlay); this.populate(); } }

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  • Has Javascript developed beyond what it was originally designed to do?

    - by Elliot Bonneville
    I've been talking with a friend about the purpose of Javascript, when and how it should be used, etc. He quoted that: JavaScript was designed to add interactivity to HTML pages [...] JavaScript gives HTML designers a programming tool HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages JavaScript can react to events A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element JavaScript can read and write HTML elements A JavaScript can read and change the content of an HTML element JavaScript can be used to validate data A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser. JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer. However, it seems like Javascript's getting used to do a lot more than these days. My friend also advocates against using Javascript's OOP functionality, claiming that "you shouldn't be processing data, merely validating." Is Javascript really limited to validating data and making flashy graphics on a web page? He goes on to claim "you shouldn't be attempting to access databases through javascript" and also says " in general you don't want to be doing your heavy lifting in javascript". I can't say I agree with his opinion, but I'd like to get some more input on this. So, my question: Has Javascript evolved from the definition above to something more powerful, has the way we use it changed, or am I just plain wrong? While I realize this is a subjective question, I can't find any more information on it, so a few links would be good, if nothing else. I'm not looking for a debate, just an answer.

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