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  • Option Trading: Getting the most out of the event session options

    - by extended_events
    You can control different aspects of how an event session behaves by setting the event session options as part of the CREATE EVENT SESSION DDL. The default settings for the event session options are designed to handle most of the common event collection situations so I generally recommend that you just use the defaults. Like everything in the real world though, there are going to be a handful of “special cases” that require something different. This post focuses on identifying the special cases and the correct use of the options to accommodate those cases. There is a reason it’s called Default The default session options specify a total event buffer size of 4 MB with a 30 second latency. Translating this into human terms; this means that our default behavior is that the system will start processing events from the event buffer when we reach about 1.3 MB of events or after 30 seconds, which ever comes first. Aside: What’s up with the 1.3 MB, I thought you said the buffer was 4 MB?The Extended Events engine takes the total buffer size specified by MAX_MEMORY (4MB by default) and divides it into 3 equally sized buffers. This is done so that a session can be publishing events to one buffer while other buffers are being processed. There are always at least three buffers; how to get more than three is covered later. Using this configuration, the Extended Events engine can “keep up” with most event sessions on standard workloads. Why is this? The fact is that most events are small, really small; on the order of a couple hundred bytes. Even when you start considering events that carry dynamically sized data (eg. binary, text, etc.) or adding actions that collect additional data, the total size of the event is still likely to be pretty small. This means that each buffer can likely hold thousands of events before it has to be processed. When the event buffers are finally processed there is an economy of scale achieved since most targets support bulk processing of the events so they are processed at the buffer level rather than the individual event level. When all this is working together it’s more likely that a full buffer will be processed and put back into the ready queue before the remaining buffers (remember, there are at least three) are full. I know what you’re going to say: “My server is exceptional! My workload is so massive it defies categorization!” OK, maybe you weren’t going to say that exactly, but you were probably thinking it. The point is that there are situations that won’t be covered by the Default, but that’s a good place to start and this post assumes you’ve started there so that you have something to look at in order to determine if you do have a special case that needs different settings. So let’s get to the special cases… What event just fired?! How about now?! Now?! If you believe the commercial adage from Heinz Ketchup (Heinz Slow Good Ketchup ad on You Tube), some things are worth the wait. This is not a belief held by most DBAs, particularly DBAs who are looking for an answer to a troubleshooting question fast. If you’re one of these anxious DBAs, or maybe just a Program Manager doing a demo, then 30 seconds might be longer than you’re comfortable waiting. If you find yourself in this situation then consider changing the MAX_DISPATCH_LATENCY option for your event session. This option will force the event buffers to be processed based on your time schedule. This option only makes sense for the asynchronous targets since those are the ones where we allow events to build up in the event buffer – if you’re using one of the synchronous targets this option isn’t relevant. Avoid forgotten events by increasing your memory Have you ever had one of those days where you keep forgetting things? That can happen in Extended Events too; we call it dropped events. In order to optimizes for server performance and help ensure that the Extended Events doesn’t block the server if to drop events that can’t be published to a buffer because the buffer is full. You can determine if events are being dropped from a session by querying the dm_xe_sessions DMV and looking at the dropped_event_count field. Aside: Should you care if you’re dropping events?Maybe not – think about why you’re collecting data in the first place and whether you’re really going to miss a few dropped events. For example, if you’re collecting query duration stats over thousands of executions of a query it won’t make a huge difference to miss a couple executions. Use your best judgment. If you find that your session is dropping events it means that the event buffer is not large enough to handle the volume of events that are being published. There are two ways to address this problem. First, you could collect fewer events – examine you session to see if you are over collecting. Do you need all the actions you’ve specified? Could you apply a predicate to be more specific about when you fire the event? Assuming the session is defined correctly, the next option is to change the MAX_MEMORY option to a larger number. Picking the right event buffer size might take some trial and error, but a good place to start is with the number of dropped events compared to the number you’ve collected. Aside: There are three different behaviors for dropping events that you specify using the EVENT_RETENTION_MODE option. The default is to allow single event loss and you should stick with this setting since it is the best choice for keeping the impact on server performance low.You’ll be tempted to use the setting to not lose any events (NO_EVENT_LOSS) – resist this urge since it can result in blocking on the server. If you’re worried that you’re losing events you should be increasing your event buffer memory as described in this section. Some events are too big to fail A less common reason for dropping an event is when an event is so large that it can’t fit into the event buffer. Even though most events are going to be small, you might find a condition that occasionally generates a very large event. You can determine if your session is dropping large events by looking at the dm_xe_sessions DMV once again, this time check the largest_event_dropped_size. If this value is larger than the size of your event buffer [remember, the size of your event buffer, by default, is max_memory / 3] then you need a large event buffer. To specify a large event buffer you set the MAX_EVENT_SIZE option to a value large enough to fit the largest event dropped based on data from the DMV. When you set this option the Extended Events engine will create two buffers of this size to accommodate these large events. As an added bonus (no extra charge) the large event buffer will also be used to store normal events in the cases where the normal event buffers are all full and waiting to be processed. (Note: This is just a side-effect, not the intended use. If you’re dropping many normal events then you should increase your normal event buffer size.) Partitioning: moving your events to a sub-division Earlier I alluded to the fact that you can configure your event session to use more than the standard three event buffers – this is called partitioning and is controlled by the MEMORY_PARTITION_MODE option. The result of setting this option is fairly easy to explain, but knowing when to use it is a bit more art than science. First the science… You can configure partitioning in three ways: None, Per NUMA Node & Per CPU. This specifies the location where sets of event buffers are created with fairly obvious implication. There are rules we follow for sub-dividing the total memory (specified by MAX_MEMORY) between all the event buffers that are specific to the mode used: None: 3 buffers (fixed)Node: 3 * number_of_nodesCPU: 2.5 * number_of_cpus Here are some examples of what this means for different Node/CPU counts: Configuration None Node CPU 2 CPUs, 1 Node 3 buffers 3 buffers 5 buffers 6 CPUs, 2 Node 3 buffers 6 buffers 15 buffers 40 CPUs, 5 Nodes 3 buffers 15 buffers 100 buffers   Aside: Buffer size on multi-processor computersAs the number of Nodes or CPUs increases, the size of the event buffer gets smaller because the total memory is sub-divided into more pieces. The defaults will hold up to this for a while since each buffer set is holding events only from the Node or CPU that it is associated with, but at some point the buffers will get too small and you’ll either see events being dropped or you’ll get an error when you create your session because you’re below the minimum buffer size. Increase the MAX_MEMORY setting to an appropriate number for the configuration. The most likely reason to start partitioning is going to be related to performance. If you notice that running an event session is impacting the performance of your server beyond a reasonably expected level [Yes, there is a reasonably expected level of work required to collect events.] then partitioning might be an answer. Before you partition you might want to check a few other things: Is your event retention set to NO_EVENT_LOSS and causing blocking? (I told you not to do this.) Consider changing your event loss mode or increasing memory. Are you over collecting and causing more work than necessary? Consider adding predicates to events or removing unnecessary events and actions from your session. Are you writing the file target to the same slow disk that you use for TempDB and your other high activity databases? <kidding> <not really> It’s always worth considering the end to end picture – if you’re writing events to a file you can be impacted by I/O, network; all the usual stuff. Assuming you’ve ruled out the obvious (and not so obvious) issues, there are performance conditions that will be addressed by partitioning. For example, it’s possible to have a successful event session (eg. no dropped events) but still see a performance impact because you have many CPUs all attempting to write to the same free buffer and having to wait in line to finish their work. This is a case where partitioning would relieve the contention between the different CPUs and likely reduce the performance impact cause by the event session. There is no DMV you can check to find these conditions – sorry – that’s where the art comes in. This is  largely a matter of experimentation. On the bright side you probably won’t need to to worry about this level of detail all that often. The performance impact of Extended Events is significantly lower than what you may be used to with SQL Trace. You will likely only care about the impact if you are trying to set up a long running event session that will be part of your everyday workload – sessions used for short term troubleshooting will likely fall into the “reasonably expected impact” category. Hey buddy – I think you forgot something OK, there are two options I didn’t cover: STARTUP_STATE & TRACK_CAUSALITY. If you want your event sessions to start automatically when the server starts, set the STARTUP_STATE option to ON. (Now there is only one option I didn’t cover.) I’m going to leave causality for another post since it’s not really related to session behavior, it’s more about event analysis. - Mike Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Option Trading: Getting the most out of the event session options

    - by extended_events
    You can control different aspects of how an event session behaves by setting the event session options as part of the CREATE EVENT SESSION DDL. The default settings for the event session options are designed to handle most of the common event collection situations so I generally recommend that you just use the defaults. Like everything in the real world though, there are going to be a handful of “special cases” that require something different. This post focuses on identifying the special cases and the correct use of the options to accommodate those cases. There is a reason it’s called Default The default session options specify a total event buffer size of 4 MB with a 30 second latency. Translating this into human terms; this means that our default behavior is that the system will start processing events from the event buffer when we reach about 1.3 MB of events or after 30 seconds, which ever comes first. Aside: What’s up with the 1.3 MB, I thought you said the buffer was 4 MB?The Extended Events engine takes the total buffer size specified by MAX_MEMORY (4MB by default) and divides it into 3 equally sized buffers. This is done so that a session can be publishing events to one buffer while other buffers are being processed. There are always at least three buffers; how to get more than three is covered later. Using this configuration, the Extended Events engine can “keep up” with most event sessions on standard workloads. Why is this? The fact is that most events are small, really small; on the order of a couple hundred bytes. Even when you start considering events that carry dynamically sized data (eg. binary, text, etc.) or adding actions that collect additional data, the total size of the event is still likely to be pretty small. This means that each buffer can likely hold thousands of events before it has to be processed. When the event buffers are finally processed there is an economy of scale achieved since most targets support bulk processing of the events so they are processed at the buffer level rather than the individual event level. When all this is working together it’s more likely that a full buffer will be processed and put back into the ready queue before the remaining buffers (remember, there are at least three) are full. I know what you’re going to say: “My server is exceptional! My workload is so massive it defies categorization!” OK, maybe you weren’t going to say that exactly, but you were probably thinking it. The point is that there are situations that won’t be covered by the Default, but that’s a good place to start and this post assumes you’ve started there so that you have something to look at in order to determine if you do have a special case that needs different settings. So let’s get to the special cases… What event just fired?! How about now?! Now?! If you believe the commercial adage from Heinz Ketchup (Heinz Slow Good Ketchup ad on You Tube), some things are worth the wait. This is not a belief held by most DBAs, particularly DBAs who are looking for an answer to a troubleshooting question fast. If you’re one of these anxious DBAs, or maybe just a Program Manager doing a demo, then 30 seconds might be longer than you’re comfortable waiting. If you find yourself in this situation then consider changing the MAX_DISPATCH_LATENCY option for your event session. This option will force the event buffers to be processed based on your time schedule. This option only makes sense for the asynchronous targets since those are the ones where we allow events to build up in the event buffer – if you’re using one of the synchronous targets this option isn’t relevant. Avoid forgotten events by increasing your memory Have you ever had one of those days where you keep forgetting things? That can happen in Extended Events too; we call it dropped events. In order to optimizes for server performance and help ensure that the Extended Events doesn’t block the server if to drop events that can’t be published to a buffer because the buffer is full. You can determine if events are being dropped from a session by querying the dm_xe_sessions DMV and looking at the dropped_event_count field. Aside: Should you care if you’re dropping events?Maybe not – think about why you’re collecting data in the first place and whether you’re really going to miss a few dropped events. For example, if you’re collecting query duration stats over thousands of executions of a query it won’t make a huge difference to miss a couple executions. Use your best judgment. If you find that your session is dropping events it means that the event buffer is not large enough to handle the volume of events that are being published. There are two ways to address this problem. First, you could collect fewer events – examine you session to see if you are over collecting. Do you need all the actions you’ve specified? Could you apply a predicate to be more specific about when you fire the event? Assuming the session is defined correctly, the next option is to change the MAX_MEMORY option to a larger number. Picking the right event buffer size might take some trial and error, but a good place to start is with the number of dropped events compared to the number you’ve collected. Aside: There are three different behaviors for dropping events that you specify using the EVENT_RETENTION_MODE option. The default is to allow single event loss and you should stick with this setting since it is the best choice for keeping the impact on server performance low.You’ll be tempted to use the setting to not lose any events (NO_EVENT_LOSS) – resist this urge since it can result in blocking on the server. If you’re worried that you’re losing events you should be increasing your event buffer memory as described in this section. Some events are too big to fail A less common reason for dropping an event is when an event is so large that it can’t fit into the event buffer. Even though most events are going to be small, you might find a condition that occasionally generates a very large event. You can determine if your session is dropping large events by looking at the dm_xe_sessions DMV once again, this time check the largest_event_dropped_size. If this value is larger than the size of your event buffer [remember, the size of your event buffer, by default, is max_memory / 3] then you need a large event buffer. To specify a large event buffer you set the MAX_EVENT_SIZE option to a value large enough to fit the largest event dropped based on data from the DMV. When you set this option the Extended Events engine will create two buffers of this size to accommodate these large events. As an added bonus (no extra charge) the large event buffer will also be used to store normal events in the cases where the normal event buffers are all full and waiting to be processed. (Note: This is just a side-effect, not the intended use. If you’re dropping many normal events then you should increase your normal event buffer size.) Partitioning: moving your events to a sub-division Earlier I alluded to the fact that you can configure your event session to use more than the standard three event buffers – this is called partitioning and is controlled by the MEMORY_PARTITION_MODE option. The result of setting this option is fairly easy to explain, but knowing when to use it is a bit more art than science. First the science… You can configure partitioning in three ways: None, Per NUMA Node & Per CPU. This specifies the location where sets of event buffers are created with fairly obvious implication. There are rules we follow for sub-dividing the total memory (specified by MAX_MEMORY) between all the event buffers that are specific to the mode used: None: 3 buffers (fixed)Node: 3 * number_of_nodesCPU: 2.5 * number_of_cpus Here are some examples of what this means for different Node/CPU counts: Configuration None Node CPU 2 CPUs, 1 Node 3 buffers 3 buffers 5 buffers 6 CPUs, 2 Node 3 buffers 6 buffers 15 buffers 40 CPUs, 5 Nodes 3 buffers 15 buffers 100 buffers   Aside: Buffer size on multi-processor computersAs the number of Nodes or CPUs increases, the size of the event buffer gets smaller because the total memory is sub-divided into more pieces. The defaults will hold up to this for a while since each buffer set is holding events only from the Node or CPU that it is associated with, but at some point the buffers will get too small and you’ll either see events being dropped or you’ll get an error when you create your session because you’re below the minimum buffer size. Increase the MAX_MEMORY setting to an appropriate number for the configuration. The most likely reason to start partitioning is going to be related to performance. If you notice that running an event session is impacting the performance of your server beyond a reasonably expected level [Yes, there is a reasonably expected level of work required to collect events.] then partitioning might be an answer. Before you partition you might want to check a few other things: Is your event retention set to NO_EVENT_LOSS and causing blocking? (I told you not to do this.) Consider changing your event loss mode or increasing memory. Are you over collecting and causing more work than necessary? Consider adding predicates to events or removing unnecessary events and actions from your session. Are you writing the file target to the same slow disk that you use for TempDB and your other high activity databases? <kidding> <not really> It’s always worth considering the end to end picture – if you’re writing events to a file you can be impacted by I/O, network; all the usual stuff. Assuming you’ve ruled out the obvious (and not so obvious) issues, there are performance conditions that will be addressed by partitioning. For example, it’s possible to have a successful event session (eg. no dropped events) but still see a performance impact because you have many CPUs all attempting to write to the same free buffer and having to wait in line to finish their work. This is a case where partitioning would relieve the contention between the different CPUs and likely reduce the performance impact cause by the event session. There is no DMV you can check to find these conditions – sorry – that’s where the art comes in. This is  largely a matter of experimentation. On the bright side you probably won’t need to to worry about this level of detail all that often. The performance impact of Extended Events is significantly lower than what you may be used to with SQL Trace. You will likely only care about the impact if you are trying to set up a long running event session that will be part of your everyday workload – sessions used for short term troubleshooting will likely fall into the “reasonably expected impact” category. Hey buddy – I think you forgot something OK, there are two options I didn’t cover: STARTUP_STATE & TRACK_CAUSALITY. If you want your event sessions to start automatically when the server starts, set the STARTUP_STATE option to ON. (Now there is only one option I didn’t cover.) I’m going to leave causality for another post since it’s not really related to session behavior, it’s more about event analysis. - Mike Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Data Virtualization: Federated and Hybrid

    - by Krishnamoorthy
    Data becomes useful when it can be leveraged at the right time. Not only enterprises application stores operate on large volume, velocity and variety of data. Mobile and social computing are in the need of operating in foresaid data. Replicating and transferring large swaths of data is one challenge faced in the field of data integration. However, smaller chunks of data aggregated from a variety of sources presents and even more interesting challenge in the industry. Over the past few decades, technology trends focused on best user experience, operating systems, high performance computing, high performance web sites, analysis of warehouse data, service oriented architecture, social computing, cloud computing, and big data. Operating on the ‘dark data’ becomes mandatory in the future technology trend, although, no solution can make dark data useful data in a single day. Useful data can be quantified by the facts of contextual, personalized and on time delivery. In most cases, data from a single source may not be complete the picture. Data has to be combined and computed from various sources, where data may be captured as hybrid data, meaning the combination of structured and unstructured data. Since related data is often found across disparate sources, effectively integrating these sources determines how useful this data ultimately becomes. Technology trends in 2013 are expected to focus on big data and private cloud. Consumers are not merely interested in where data is located or how data is retrieved and computed. Consumers are interested in how quick and how the data can be leveraged. In many cases, data virtualization is the right solution, and is expected to play a foundational role for SOA, Cloud integration, and Big Data. The Oracle Data Integration portfolio includes a data virtualization product called ODSI (Oracle Data Service Integrator). Unlike other data virtualization solutions, ODSI can perform both read and write operations on federated/hybrid data (RDBMS, Webservices,  delimited file and XML). The ODSI Engine is built on XQuery, hence ODSI user can perform computations on data either using XQuery or SQL. Built in data and query caching features, which reduces latency in repetitive calls. Rightly positioning ODSI, can results in a highly scalable model, reducing spend on additional hardware infrastructure.

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  • Should I choose KVM/XEN over OpenVZ or use them together?

    - by Krystian
    I've got a dual xeon e5504 server, with [for now] only 8GB of ram. Storage is'n impressive either: 3x 146GB sas in raid5 + 500GB sata drives. Currently it works as a development server, but it's over speced for our needs and since our development methods changed through last 2 years we decided it will work as a production system for some of our applications + we would like to have a separate system for testing/research. Our apps are mainly web apps deployed on tomcats [plural as some of the apps require older versions] and connected to Postgres. I would like to have a production system, where only httpd+tomcat+db are setup and nothing else runs there. Sterile system. Apart from that, I would like a test system, where I can play with different JVM settings, deploy my test apps, play with tomcat/httpd settings and restart them without interfering with the production system. Apart from that, I would like to be able to play with different linux flavors, with newer kernels to test how they work etc. I know, this is not possible with OpenVZ and I would have to choose KVM for that. I am thinking about merging the two, and setting up a KVM to be able to work with different systems [linux only to be frank] + use openVZ to setup separate machines for my development needs. I would simply go with that, but reading here and there about the performance impact full virtualization has over containers and looking at the specs of my server makes me think twice about it. I don't want to loose too much performance, especially because of the nature of my apps [few JVMs running at the same time]. It will be my first time with virtualization, apart from using desktop virtualbox/vmserver. Although I am a fast learner I don't want to mess with the main system so much that it will break the production apps or make them crawl. Although they are more or less internal apps and they don't produce much load, they need to be stable. I've read, that KVM host is a normal linux installation and it allows to run normal processes on it. If that is so, does it allow to run openVZ as well? I mean... can I have KVM and OpenVZ running on the same system/kernel? Or do I have to setup another system to run OpenVZ containers? How much performance impact can this have for me? Will my hardware suffice? oh and one more thing... unfortunately I'm quite limited with the funds... I'm looking for a free solution only :/

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  • Google Chrome: JavaScript associative arrays, evaluated out of sequence

    - by Jerry
    Ok, so on a web page, I've got a JavaScript object which I'm using as an associative array. This exists statically in a script block when the page loads: var salesWeeks = { "200911" : ["11 / 2009", "Fiscal 2009"], "200910" : ["10 / 2009", "Fiscal 2009"], "200909" : ["09 / 2009", "Fiscal 2009"], "200908" : ["08 / 2009", "Fiscal 2009"], "200907" : ["07 / 2009", "Fiscal 2009"], "200906" : ["06 / 2009", "Fiscal 2009"], "200905" : ["05 / 2009", "Fiscal 2009"], "200904" : ["04 / 2009", "Fiscal 2009"], "200903" : ["03 / 2009", "Fiscal 2009"], "200902" : ["02 / 2009", "Fiscal 2009"], "200901" : ["01 / 2009", "Fiscal 2009"], "200852" : ["52 / 2008", "Fiscal 2009"], "200851" : ["51 / 2008", "Fiscal 2009"] }; The order of the key/value pairs is intentional, as I'm turning the object into an HTML select box such as this: <select id="ddl_sw" name="ddl_sw"> <option value="">== SELECT WEEK ==</option> <option value="200911">11 / 2009 (Fiscal 2009)</option> <option value="200910">10 / 2009 (Fiscal 2009)</option> <option value="200909">09 / 2009 (Fiscal 2009)</option> <option value="200908">08 / 2009 (Fiscal 2009)</option> <option value="200907">07 / 2009 (Fiscal 2009)</option> <option value="200906">06 / 2009 (Fiscal 2009)</option> <option value="200905">05 / 2009 (Fiscal 2009)</option> <option value="200904">04 / 2009 (Fiscal 2009)</option> <option value="200903">03 / 2009 (Fiscal 2009)</option> <option value="200902">02 / 2009 (Fiscal 2009)</option> <option value="200901">01 / 2009 (Fiscal 2009)</option> <option value="200852">52 / 2008 (Fiscal 2009)</option> <option value="200851">51 / 2008 (Fiscal 2009)</option> </select> ...with code that looks like this (snipped from a function): var arr = []; arr.push( "<select id=\"ddl_sw\" name=\"ddl_sw\">" + "<option value=\"\">== SELECT WEEK ==</option>" ); for(var key in salesWeeks) { arr.push( "<option value=\"" + key + "\">" + salesWeeks[key][0] + " (" + salesWeeks[key][1] + ")" + "<\/option>" ); } arr.push("<\/select>"); return arr.join(""); This all works fine in IE, FireFox and Opera. However in Chrome, the order comes out all weird: <select id="ddl_sw" name="ddl_sw"> <option value="">== SELECT WEEK ==</option> <option value="200852">52 / 2008 (Fiscal 2009)</option> <option value="200908">08 / 2009 (Fiscal 2009)</option> <option value="200906">06 / 2009 (Fiscal 2009)</option> <option value="200902">02 / 2009 (Fiscal 2009)</option> <option value="200907">07 / 2009 (Fiscal 2009)</option> <option value="200904">04 / 2009 (Fiscal 2009)</option> <option value="200909">09 / 2009 (Fiscal 2009)</option> <option value="200903">03 / 2009 (Fiscal 2009)</option> <option value="200905">05 / 2009 (Fiscal 2009)</option> <option value="200901">01 / 2009 (Fiscal 2009)</option> <option value="200910">10 / 2009 (Fiscal 2009)</option> <option value="200911">11 / 2009 (Fiscal 2009)</option> <option value="200851">51 / 2008 (Fiscal 2009)</option> </select> NOTE: This order, though weird, does not change on subsequent refreshes. It's always in this order. So, what is Chrome doing? Some optimization in how it processes the loop? In the first place, am I wrong to rely on the order that the key/value pairs are declared in any associative array? I never questioned it before, I just assumed the order would hold because this technique has always worked for me in the other browsers. But I suppose I've never seen it stated anywhere that the order is guaranteed. Maybe it's not? Any insight would be awesome. Thanks.

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  • Bridging: Loosing WLAN network connection with 4addr on option - Why?

    - by WitchCraft
    Question: For use with my Xen VM, I need to create a virtual network interface (vif) that is bridged to wlan0. If in /etc/network/interfaces I add auto xenbr0 iface xenbr0 inet dhcp And then later do brctl addif xenbr0 wlan0 I get this error message. can't add wlan0 to bridge xenbr0: Operation not supported I found out that Linux won't let you bridge a wireless interface in managed mode at all unless you enable the 4addr option (needed to recompile iw): iw dev wlan0 set 4addr on Afterwards brctl addif xenbr0 wlan0 works, and brctl show shows xenbr0 as bridged to wlan0. Unfortunately, as soon as I execute iw dev wlan0 set 4addr on my entire network connection is gone (no connection). As soon as then I execute iw dev wlan0 set 4addr off I reconnect and it works again. If I re-execute 4addr on, it breaks again, if I execute 4addr off, it works again. Unfortunately, I can't just turn 4addr on, activate the bridge and then turn it back off (error: device not ready). Does anybody know why I loose my connection ?

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  • What jQuery is triggered when a user selects a "drop down list" option

    - by Ankur
    I want to display a different form for different selections of this drop down list: <label> <select name="type" id="type"> <option value="object" selected="selected">Object</option> <option value="number">Number</option> <option value="text">Text</option> <option value="date">Date</option> <option value="time">Time</option> <option value="geo">Geospatial</option> <option value="currency">Currency</option> </select> </label> What would be the jQuery event that is triggered when a user selects one of these options. Would the .click() event be triggered in this case as well?

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  • Hover image - part of forms appears untill hover another How?

    - by Mac
    Im trying to make part of my form/questionnaire appears when hover on image and stay active untill hover another image next to it. and repeat it on 7 images. Of course I need the cheched checkboxes to stay after they'll be hidden so you can come back to them by hover the image and for ex. correct answers and so on.. I was using a j code: <script type="text/javascript"> $("#Oobj51").hover(function(){ $('#Oobj58').show(); },function(){ $('#Oobj58').hide(); }); </script> it works to another elements on my page but not to the form. how can i do it maybe with css class or another j code. Thanks! Parts of html: (let's say I want to hover on "Oobj56" and make "Oobj58" appears and stay as I said before...) <div id="Oobj56"> <button type="submit" class="przed6" onmouseover="this.className='po6'" onmouseout="this.className='przed6'" /> </div> <div id="Oobj57"> <button type="submit" class="przed7" onmouseover="this.className='po7'" onmouseout="this.className='przed7'" /> </div> <div id="Oobj60"> <form action="mailto:" method="post" enctype="text/plain"> <div id="Oobj59"> <input type="text" input size="8" name="imie" placeholder="imie"> <input type="text" input size="11" name="numer" placeholder="numer telefonu"> <br><br> <select name="miasto"> <option selected="Miasto">Miasto</option> <option>Wroclaw</option> <option>Warszawa</option> <option>Kraków</option> <option>Trójmiasto</option> <option>Poznan</option> <option>Szczecin</option> <option>Torun</option> <option>Lódz</option> <option>Bydgoszcz</option> <option>Lublin</option> <option>Katowice</option> </select> <select name="wiek"> <option selected="selected">Wiek</option> <option> <15 </option> <option>15-19</option> <option>20-24</option> <option>25-29</option> <option>30-34</option> <option>35-39</option> <option>40-44</option> <option>45-49</option> <option>50-54</option> <option>55-59</option> <option>60-64</option> <option>65-69</option> <option>70-74</option> <option> >75 </option> </select> <select name="plec"> <option selected="selected">Plec</option> <option>Mezczyzna</option> <option>Kobieta</option> </select></div> <div id="Oobj58"> <script language="JavaScript"> function toggle(source) { checkboxes = document.getElementsByName('sport'); for(var i=0, n=checkboxes.length;i<n;i++) { checkboxes[i].checked = source.checked; } } </script> <input type="checkbox" onClick="toggle(this)" /><br> <input type="checkbox" name="sport" value="gym" />silownia<br /> <input type="checkbox" name="sport" value="fitness" />fitness<br /> <input type="checkbox" name="sport" value="noga" />pilka nozna<br /> <input type="checkbox" name="sport" value="kosz" />koszykówka<br /> <input type="checkbox" name="sport" value="siata" />siatkówka<br /> <input type="checkbox" name="sport" value="ameryka" />football amerykanski<br /> <input type="checkbox" name="sport" value="konie" />jezdziectwo konne<br /> <input type="checkbox" name="sport" value="basen" />basen/sporty wodne<br /> <input type="checkbox" name="sport" value="zima" />sporty zimowe<br /> </div> <div id="Oobj15"> <input type="submit" style="font-family: Open Sans;" value="Wyslij" class="wyslij" /> </div></form> </div>

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  • How to makesure VM is in Para virtualization mode on XEN?

    - by ananthan
    I am having a server running XEN,with ubuntu 12.04 as Domain 0. Intel VT is turned on by default and i dont want to run any Windows OS as VM. So 1. how can i makesure that all the created VM will be in paravirtualized mode even with VT enabled? I have heard that in Full Virtualization hypervisor needs to work hard for emulating all the underlying hardware,which may reduce performance for too much i/o specific applications when compared to para mode. 2.Since i am running only Linux VMs do i really need to enable VT support? 3.Can i be able to run Linux VM in para mode with VT enabled? 4.Will simply turning on VT support changes virtualization from para to full virtualization?? 5.Will there be any performance improvement for VM running Linux OS if VT is enabled?

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  • Should the virtualization host be allowed to run any service?

    - by Giordano
    I recently setup a virtualization server for the small company I'm running. This server runs few virtual machines that are used for development, testing, etc... My business partner works from a remote location, thus I also installed a vpn server on the virtualization host to make it possible for him to safely reach the company services. Moreover, again on the virtualization host, I installed bacula to perform the backup of the data. Is it advisable/good practice to do so or should I create one more virtual machine to do backups and VPN? Is it a bad idea to run these services on the host itself? If yes, why? Thanks in advance!

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  • How to use JQuery to set the value of 2 html form select elements depending on the value of another

    - by Chris Stevenson
    My Javascript and JQuery skills are poor at best and this is ** I have the following three elements in a form : <select name="event_time_start_hours"> <option value="blank" disabled="disabled">Hours</option> <option value="blank" disabled="disabled">&nbsp;</option> <option value="01">1</option> <option value="02">2</option> <option value="03">3</option> <option value="04">4</option> <option value="05">5</option> <option value="06">6</option> <option value="07">7</option> <option value="08">8</option> <option value="09">9</option> <option value="10">10</option> <option value="11">11</option> <option value="12">12</option> <option value="midnight">Midnight</option> <option value="midday">Midday</option> </select> <select name="event_time_start_minutes"> <option value="blank" disabled="disabled">Minutes</option> <option value="blank" disabled="disabled">&nbsp;</option> <option value="00">00</option> <option value="15">15</option> <option value="30">30</option> <option value="45">45</option> </select> <select name="event_time_start_ampm"> <option value="blank" disabled="disabled">AM / PM</option> <option value="blank" disabled="disabled">&nbsp;</option> <option value="am">AM</option> <option value="pm">PM</option> </select> Quite simply, when either 'midnight' or 'midday' is selected in "event_time_start_hours", I want the values of "event_time_start_minutes" and "event_time_start_ampm" to change to "00" and "am" respectively. My VERY poor piece of Javascript says this so far : $(document).ready(function() { $('#event_time_start_hours').change(function() { if($('#event_time_start_hours').val('midnight')) { $('#event_time_start_minutes').val('00'); } }); }); ... and whilst I'm not terribly surprised it doesn't work, I'm at a loss as to what to do next. I want to do this purely for visual reasons for the user as when the form submits I ignore the "minutes" and "am/pm". I'm trying to decide whether it would be best to change the selected values, change the selected values and then disable the element or hide them altogether. However, without any success in getting anything to happen at all I haven't been able to try the different approaches to see what feels right. I've ruled out the obvious things like a duplicate element ID or simply not linking to JQuery. Thank you.

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  • How to simplify my country select menu PHP/mysql

    - by user342391
    I have a select menu that displays countries. It looks at the DB and judging by the value in the db shows the option as selected. Is there a simpler way off doing this than: if ($country == 'AG') {echo '<option value="AG" selected="selected">Antigua</option>';} else {echo '<option value="AG">Antigua</option>';}; if ($country == 'AR') {echo '<option value="AR" selected="selected">Argentina</option>';} else {echo '<option value="AR">Argentina</option>';}; if ($country == 'AM') {echo '<option value="AM" selected="selected">Armenia</option>';} else {echo '<option value="AM">Armenia</option>';}; if ($country == 'AW') {echo '<option value="AW" selected="selected">Aruba</option>';} else {echo '<option value="AW">Aruba</option>';}; if ($country == 'AU') {echo '<option value="AU" selected="selected">Australia</option>';} else {echo '<option value="AU">Australia</option >';}; if ($country == 'AT') {echo '<option value="AT" selected="selected">Austria</option>';} else {echo '<option value="AT">Austria</option>';}; if ($country == 'AZ') {echo '<option value="AZ" selected="selected">Azerbaijan</option>';} else {echo '<option value="AZ">Azerbaijan</option>';}; if ($country == 'BS') {echo '<option value="BS" selected="selected">Bahamas</option>';} else {echo '<option value="BS">Bahamas</option>';}; if ($country == 'BH') {echo '<option value="BH" selected="selected">Bahrain</option>';} else {echo '<option value="BH">Bahrain</option>';}; There are a lot of countries and doing this would be madness wouldn't it????

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  • How is application virtualization implemented?

    - by noob_lurker
    I am trying to understand how software like App-V and sandboxie (http://www.sandboxie.com/) work. But for the life of me, I can't think of anything that could make this possible. How do they intercept API calls and trick the target software? If someone would say that it's just magic and pixie dust, I would believe them. Seriously though, are there any white papers that discuss solutions to this problem? If this is possible on the CLR level then that would be good but I'm willing to go native if I have to.

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  • JQuery get id or class, not value

    - by Celia Tan
    I'm new at JQuery, what I wanted to ask is how to select an option, then another option will automatic selected that have property of first option. I've given code like this: <select name="kendaraan"> <option value="" selected>pilih kendaraan!</option> <option value="B 2011 DR" class="B2011DR">B 2011 DR</option> <option value="R 3333 OKI" class="R3333OKI">R 3333 OKI</option> <option value="k03">jazz</option> <option value="k04">innova</option> </select> <select name="driver"> <option value="" selected>pilih kendaraan!</option> <option value="s02" car="B2011DR" style="display:none">jojon</option> <option value="s01" car="B2011DR" style="display:none">mamat</option> <option value="s04" car="R3333OKI" style="display:none">tukul</option> <option value="s03" car="R3333OKI" style="display:none">mamat</option> <option value="s07" car="k03" style="display:none">bejo</option> <option value="s05" car="k03" style="display:none">mamat</option> <option value="s06" car="k03" style="display:none">tukul</option> <option value="s08" car="k04" style="display:none">budi</option> <option value="s09" car="">komeng</option> </select> $('select[name=kendaraan]').change(function() { //hide all option $('select[name=driver] option').css('display','none'); //display option only for matched driver var isCar = $('select[name=driver] option[car='+$(this).val()+']'); isCar.css('display','block'); //auto select first matched diriver $('select[name=driver]').val( $(isCar[0]).val() ) }) But the jquery code is for getting the value of "kendaraan", how to match it with the class, not the value?

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