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Search found 134 results on 6 pages for 'piping'.

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  • Pipelining String in Powershell

    - by ChvyVele
    I'm trying to make a simple PowerShell function to have a Linux-style ssh command. Such as: ssh username@url I'm using plink to do this, and this is the function I have written: function ssh { param($usernameAndServer) $myArray = $usernameAndServer.Split("@") $myArray[0] | C:\plink.exe -ssh $myArray[1] } If entered correctly by the user, $myArray[0] is the username and $myArray[1] is the URL. Thus, it connects to the URL and when you're prompted for a username, the username is streamed in using the pipeline. Everything works perfectly, except the pipeline keeps feeding the username ($myArray[0]) and it is entered as the password over and over. Example: PS C:\Users\Mike> ssh xxxxx@yyyyy login as: xxxxx@yyyyy's password: Access denied xxxxx@yyyyy's password: Access denied xxxxx@yyyyy's password: Access denied xxxxx@yyyyy's password: Access denied xxxxx@yyyy's password: Access denied xxxxx@yyyyy's password: FATAL ERROR: Server sent disconnect message type 2 (protocol error): "Too many authentication failures for xxxxx" Where the username has been substituted with xxxxx and the URL has been substituted with yyyyy. Basically, I need to find out how to stop the script from piping in the username ($myArray[0]) after it has been entered once. Any ideas? I've looked all over the internet for a solution and haven't found anything.

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  • free open-source linux screenshot & ocr tool

    - by Gryllida
    I'm looking for a tool which would be able to capture a screen region, pass it to OCR and put the result into clipboard. "import ppm:- | gocr -i - | xclip -selection c" works, but gocr is unreliable: simple text on a webpage has errors. It is a clear font but the OCR tool always misses "r" and replaces it with underscore. "import ppm:- | ocrad -i - | xclip -selection c" says "ocrad: maxval 255 in ppm "P6" file." tesseract needs an image file and does not accept piping input to it. xfce4-screenshooter does not do OCR. ABBYY Screenshot Reader is proprietary. tessnet2 is freeware running on a proprietary platform. Google Docs can OCR screenshots in a batch. But my data is confidential and better not put online. Graphical interface solutions would be acceptable for this question, too. There is a number of existing SuperUser questions about OCR. They fall in several categories. Questions just about OCR without the "screenshot taking" part. Open Source OCR for linux Free OCR for Arabic text Looking for recommendations on OCR problem - tabular numeric data Which has better OCR applications: Ubuntu, or Mac/iPad, or Windows? How can I preform OCR from the command line? OCR solution on linux machine from command line (duplicate) Free OCR software OCR for Sanskrit ( OR devanagari) Copy image and paste to OCR (windows) File processing OCR instead of screenshot. Online OCR website for processing an entire pdf file at one time? Practical OCR solution for converting a large book to a digital format? How to extract text with OCR from a PDF on Linux? Batch-OCR many PDFs OCR Image based PDF Copy image and paste to OCR Extract OCR text from Evernote OCR in Word 2013 Replace (OCR) garbled text in PDF? Process files prior to running OCR. How can I make OCR recognize my documents' text better? Tesseract OCR recognition bilingual document. mistakes tolerance level setup OCR for low quality images How do I get the best quality screenshot for OCR (Optical Character Recognition) and what tool would be the best for screenshots? OCR training. Training Tesseract-OCR for english language fonts None of them answer this question.

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  • With CentOS 6 and LXC, "ifconfig" is unable to see network interface (but busybox "ifconfig" works fine)

    - by larsks
    I've just started working with LXC under CentOS 6 (via the libvirt adapter). If I create an LXC container, I'm unable to see any network interfaces when using the native system tools: # ifconfig -a # The behavior is very odd; specifying an interface by names yields neither the expected output nor an error message. This is true even for clearly invalid interface names, like this: # ifconfig foo # The ip command exhibits the same behavior. On the other hand, if I use "ifconfig" provided by busybox, everything works as expected: # busybox ifconfig -a eth0 Link encap:Ethernet HWaddr 52:54:00:E0:12:C8 inet6 addr: fe80::5054:ff:fee0:12c8/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:268 errors:0 dropped:0 overruns:0 frame:0 TX packets:6 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:17814 (17.3 KiB) TX bytes:552 (552.0 B) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) So...what does busybox know that the native tools don't? The libvirt config for this environment is pretty standard; the network definition looks like this: <interface type='network'> <mac address='52:54:00:e0:12:c8'/> <source network='default'/> <target dev='veth0'/> </interface> The full configuration is here if you think it might help. I'm running: lxc-0.7.2-2.el6.x86_64 kernel-2.6.32-71.29.1.el6.x86_64 EDIT Weirder and weirder...it's a display issue, not a functionality issue. I can see the output of ifconfig if I pipe it into anything, so for example: # ifconfig eth0 | cat eth0 Link encap:Ethernet HWaddr 52:54:00:E0:12:C8 inet addr:192.168.10.10 Bcast:192.168.10.255 Mask:255.255.255.0 inet6 addr: fe80::5054:ff:fee0:12c8/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:573 errors:0 dropped:0 overruns:0 frame:0 TX packets:6 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:37914 (37.0 KiB) TX bytes:552 (552.0 b) And in fact even when not piping the output, strace shows that ifconfig is in fact writing the output to file descriptor 1 (aka stdout), so it's not clear why no output is actually showing up. This could be either an LXC or a virsh issue, I guess.

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  • find words in a hashset or treeset?

    - by icelated
    I am piping in a file and storing it into a treeset. I am trying to count unique words.. I am placing words that i dont want into a hashset. "a","the", "and" I want to check to see if the file contains those words, before i place them into the TreeSet.. i know i need some sort of if(word == find) ? i just dont know how to do it.. Sorry about formatting. its hard to get it correct after you paste. this is what i have.. import java.util.Scanner; import java.util.ArrayList; import java.util.TreeSet; import java.util.Iterator; import java.util.HashSet; public class Project1 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String word; String grab; int count = 0; int count2 =0; int count3 =0; int count4 =0; int number; TreeSet<String> a = new TreeSet<String>(); HashSet<String> find = new HashSet<String>(); System.out.println("Project 1\n"); find.add("a"); find.add("and"); find.add("the"); while (sc.hasNext()) { word = sc.next(); word = word.toLowerCase(); for(int i = 0; i < word.length(); i++ ) { if(Character.isDigit(word.charAt(i))) { count3++; } } //if( a.contains("a") ) //|| word.matches("and") || word.matches("the")|| word.contains("$")) //{ // count2++; // } a.add(word); if (word.equals("---")) { break; } } System.out.println("a size"); System.out.println(a.size()); // count = count2 - count; System.out.println("unique words"); System.out.println(a.size() - count2 - count3); System.out.println("\nbye..."); } }

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  • Modify audio pitch of recorded clip (m4v)

    - by devcube
    I'm writing an app in which I'm trying to change the pitch of the audio when I'm recording a movie (.m4v). Or by modifying the audio pitch of the movie afterwards. I want the end result to be a movie (.m4v) that has the original length (i.e. same visual as original) but with modified sound pitch, e.g. a "chipmunk voice". A realtime conversion is to prefer if possible. I've read alot about changing audio pitch in iOS but most examples focus on playback, i.e. playing the sound with a different pitch. In my app I'm recording a movie (.m4v / AVFileTypeQuickTimeMovie) and saving it using standard AVAssetWriter. When saving the movie I have access to the following elements where I've tried to manipulate the audio (e.g. modify the pitch): audio buffer (CMSampleBufferRef) audio input writer (AVAssetWriterAudioInput) audio input writer options (e.g. AVNumberOfChannelsKey, AVSampleRateKey, AVChannelLayoutKey) asset writer (AVAssetWriter) I've tried to hook into the above objects to modify the audio pitch, but without success. I've also tried with Dirac as described here: Real Time Pitch Change In iPhone Using Dirac And OpenAL with AL_PITCH as described here: Piping output from OpenAL into a buffer And the "BASS" library from un4seen: Change Pitch/Tempo In Realtime I haven't found success with any of the above libs, most likely because I don't really know how to use them, and where to hook them into the audio saving code. There seems to be alot of librarys that have similar effects but focuses on playback or custom recording code. I want to manipulate the audio stream I've already got (AVAssetWriterAudioInput) or modify the saved movie clip (.m4v). I want the video to be unmodifed visually, i.e. played at the same speed. But I want the audio to go faster (like a chipmunk) or slower (like a ... monster? :)). Do you have any suggestions how I can modify the pitch in either real time (when recording the movie) or afterwards by converting the entire movie (.m4v file)? Should I look further into Dirac, OpenAL, SoundTouch, BASS or some other library? I want to be able to share the movie to others with modified audio, that's the reason I can't rely on modifying the pitch for playback only. Any help is appreciated, thanks!

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  • Server Cabinet/Room Cooling

    - by user37226
    Hello all. I currently have two desktops and three servers in my office sitting on the floor (I know this is bad). With that many servers the ambient temperature in the room goes up quickly. I am located in Dallas, TX so during the winter, if the heat is kept low, it is not a problem, but during the summer it easily jumps the room +10 degrees. I have decided and found a free 42U server cabinet that a hosting company was throwing away to house all of these systems in. One server is in a rack mount case while the other four servers are housed in mid-tower cases. I have purchased shelves for each computer and plan to lay the towers side ways on these shelves (as replacing the cases costs a heck of a lot of money). I like the idea of housing all of these systems in the cabinet because it will save a lot of room and clean up all of the cabling currently laying all over the office floor. When putting this setup together over the next couple of weeks, I want to address issues with dust and cooling. The server cabinet has a fan on top, front plexiglass door and a rear metal door with vent wholes on the bottom. First the cooling issues. I know I am going to want to have cool air enter the bottom of the cabinet and exit the top. I do not want the room heating up though as this will make my work area hot and then make the servers warmer as the air eventually reenters the cabinet. I had an idea to fix this problem, but am unsure if it will work. I was thinking of taking flexible piping and adapting it to the back fans of the computer having the other end of the pipe at the top close to the cabinet's top mounted fan. I was then thinking of creating a duct around the top fan into the attic. Now I am very concerned that the attic will cause issues with this type of setup because during July/August time frame, the attic is easily 120 degrees F. I could also use the flexible pipe to take it to an attic exhaust vent if it would be better to vent it into the 100 degree air outside (at least there may be wind. The other option would be to buy a small portable air conditioner. This may be a possibility, but do I want to spend the extra money on power? I bet this increases the noise. Plus they are around $250 on Amazon. What would you all recommend? Depending on the solution I end up running with above, I would also like to limit the dust that gets into the cabinet. If I were to cut a whole and mount a second cabinet fan on the bottom of the rear door, could I possibly mount a standard home air filter on the other side of that whole? Thanks in advance for your recommendations. I look forward to reading your interesting ideas.

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  • Server Cabinet/Room Cooling

    - by user37226
    Hello all. I currently have two desktops and three servers in my office sitting on the floor (I know this is bad). With that many servers the ambient temperature in the room goes up quickly. I am located in Dallas, TX so during the winter, if the heat is kept low, it is not a problem, but during the summer it easily jumps the room +10 degrees. I have decided and found a free 42U server cabinet that a hosting company was throwing away to house all of these systems in. One server is in a rack mount case while the other four servers are housed in mid-tower cases. I have purchased shelves for each computer and plan to lay the towers side ways on these shelves (as replacing the cases costs a heck of a lot of money). I like the idea of housing all of these systems in the cabinet because it will save a lot of room and clean up all of the cabling currently laying all over the office floor. When putting this setup together over the next couple of weeks, I want to address issues with dust and cooling. The server cabinet has a fan on top, front plexiglass door and a rear metal door with vent wholes on the bottom. First the cooling issues. I know I am going to want to have cool air enter the bottom of the cabinet and exit the top. I do not want the room heating up though as this will make my work area hot and then make the servers warmer as the air eventually reenters the cabinet. I had an idea to fix this problem, but am unsure if it will work. I was thinking of taking flexible piping and adapting it to the back fans of the computer having the other end of the pipe at the top close to the cabinet's top mounted fan. I was then thinking of creating a duct around the top fan into the attic. Now I am very concerned that the attic will cause issues with this type of setup because during July/August time frame, the attic is easily 120 degrees F. I could also use the flexible pipe to take it to an attic exhaust vent if it would be better to vent it into the 100 degree air outside (at least there may be wind. The other option would be to buy a small portable air conditioner. This may be a possibility, but do I want to spend the extra money on power? I bet this increases the noise. Plus they are around $250 on Amazon. What would you all recommend? Depending on the solution I end up running with above, I would also like to limit the dust that gets into the cabinet. If I were to cut a whole and mount a second cabinet fan on the bottom of the rear door, could I possibly mount a standard home air filter on the other side of that whole? Thanks in advance for your recommendations. I look forward to reading your interesting ideas.

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  • Specifying a Postfix Instance to send outbound email

    - by Catherine Jefferson
    I have a CentOS 6.5 server running Postfix 2.6x (the default distribution) with five public IPv4 IPs bound to it. Each IP has DNS and rDNS set separately. Each uses a different hostname at a different domain. I have five Postfix instances, one bound to each IP, like this example: 192.168.34.104 red.example.com /etc/postfix 192.168.36.48 green.example.net /etc/postfix-green 192.168.36.49 pink.example.org /etc/postfix-pink 192.168.36.50 orange.example.info /etc/postfix-orange 192.168.36.51 blue.example.us /etc/postfix-blue I've tested each IP by telneting to port 25. Postfix answers and banners properly with the correct hostname. Email is received on all of these instances with no problems and is routed to the correct place. This setup, minus the final instance, has existed for a couple of years and works. I never bothered to set up outbound email to go through any but the main instance, however; there was no need. Now I need to send email from blue.example.us that actually leaves from that interface and IP, such that the Received headers show blue.example.us as the sending mailhost, so that SPF and DKIM validate, etc etc. The email that will be sent from blue.example.com is a feedback loop sent by a single shell account on the server (account5), an account that is dedicated to sending this email. The account receives the feedback loop emails from servers on other networks, saves the bodies of those emails, and then generates a new outbound email header, appends the saved body, and sends the email. It's sending by piping each email to sendmail -oi -t. We're doing it this way to mask the identities of the initial servers. The procmail script that processes these emails works correctly. However, I cannot configure this account to send email through the proper Postfix instance/IP/interface. The exact same account and script sends email through the main Postfix instance /etc/postfix without any issues. When I change MAIL_CONFIG to point to /etc/postfix-blue in either .bash_profile or the Procmail script that handles this email, though, I get this error: sendmail: fatal: User account5(###) is not allowed to submit mail I've read the manuals on Postfix.org, searched Google, and tried the suggestions in three previous answers here on ServerFault.com: Postfix - specify interface to deliver outbound mail on Postfix user is not allowed to submit mail Postfix rejects php mails I have been careful to stop and restart Postfix after each configuration change, and tested the results. Nothing has worked. The main postfix instance happily accepts outbound email from account5. The postfix-blue instance continues to reject email from account5 with the sendmail error above. As tempting as it is to blame machine hostility, I know that I must be missing something or doing something wrong. Does anybody have any suggestions as to what it might be? Please feel free to ask for further information about my setup if you need it. =-=-=-=-=-=-=-=-=-= At the request of the responder, here are main.cf and master.cf for a) the main postfix instance ("red.example.com") and b) the FBL instance ("blue.example.us") [NOTE: All parameters not specified below were left at the default Postfix 2.6 settings] MAIN: master.cf smtp inet n - n - - smtpd main.cf myhostname = red.example.com mydomain = example.com inet_interfaces = $myhostname, localhost inet_protocols = all lmtp_host_lookup = native smtp_host_lookup = native ignore_mx_lookup_error = yes mydestination = $myhostname, localhost.$mydomain, localhost local_recipient_maps = mynetworks = 192.168.34.104/32 relay_domains = example.com, example.info, example.net, example.org, example.us relayhost = [192.168.34.102] # Separate physical server, main mailserver. relay_recipient_maps = hash:/etc/postfix/relay_recipients alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases smtpd_banner = $myhostname ESMTP $mail_name multi_instance_wrapper = ${command_directory}/postmulti -p -- multi_instance_enable = yes multi_instance_directories = /etc/postfix-green /etc/postfix-pink /etc/postfix-orange /etc/postfix-blue FBL: master.cf 184.173.119.103:25 inet n - n - - smtpd main.cf myhostname = blue.example.us mydomain = blue.example.us <= Deliberately set to subdomain only. myorigin = $mydomain inet_interfaces = $myhostname lmtp_host_lookup = native smtp_host_lookup = native ignore_mx_lookup_error = yes mydestination = $myhostname local_recipient_maps = unix:passwd.byname $alias_maps $virtual_alias_maps mynetworks = 192.168.36.51/32, 192.168.35.20/31 <= Second IP is backup MX servers relay_domains = $mydestination recipient_canonical_maps = hash:/etc/postfix-blue/canonical virtual_alias_maps = hash:/etc/postfix-fbl/virtual alias_maps = hash:/etc/aliases, hash:/etc/postfix-blue/canonical alias_maps = hash:/etc/aliases, hash:/etc/postfix-blue/canonical mailbox_command = /usr/bin/procmail -a "$EXTENSION" DEFAULT=$HOME/Mail/ MAILDIR=$HOME/Mail smtpd_banner = $myhostname ESMTP $mail_name authorized_submit_users = multi_instance_name = postfix-blue multi_instance_enable = yes

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  • Spooling in SQL execution plans

    - by Rob Farley
    Sewing has never been my thing. I barely even know the terminology, and when discussing this with American friends, I even found out that half the words that Americans use are different to the words that English and Australian people use. That said – let’s talk about spools! In particular, the Spool operators that you find in some SQL execution plans. This post is for T-SQL Tuesday, hosted this month by me! I’ve chosen to write about spools because they seem to get a bad rap (even in my song I used the line “There’s spooling from a CTE, they’ve got recursion needlessly”). I figured it was worth covering some of what spools are about, and hopefully explain why they are remarkably necessary, and generally very useful. If you have a look at the Books Online page about Plan Operators, at http://msdn.microsoft.com/en-us/library/ms191158.aspx, and do a search for the word ‘spool’, you’ll notice it says there are 46 matches. 46! Yeah, that’s what I thought too... Spooling is mentioned in several operators: Eager Spool, Lazy Spool, Index Spool (sometimes called a Nonclustered Index Spool), Row Count Spool, Spool, Table Spool, and Window Spool (oh, and Cache, which is a special kind of spool for a single row, but as it isn’t used in SQL 2012, I won’t describe it any further here). Spool, Table Spool, Index Spool, Window Spool and Row Count Spool are all physical operators, whereas Eager Spool and Lazy Spool are logical operators, describing the way that the other spools work. For example, you might see a Table Spool which is either Eager or Lazy. A Window Spool can actually act as both, as I’ll mention in a moment. In sewing, cotton is put onto a spool to make it more useful. You might buy it in bulk on a cone, but if you’re going to be using a sewing machine, then you quite probably want to have it on a spool or bobbin, which allows it to be used in a more effective way. This is the picture that I want you to think about in relation to your data. I’m sure you use spools every time you use your sewing machine. I know I do. I can’t think of a time when I’ve got out my sewing machine to do some sewing and haven’t used a spool. However, I often run SQL queries that don’t use spools. You see, the data that is consumed by my query is typically in a useful state without a spool. It’s like I can just sew with my cotton despite it not being on a spool! Many of my favourite features in T-SQL do like to use spools though. This looks like a very similar query to before, but includes an OVER clause to return a column telling me the number of rows in my data set. I’ll describe what’s going on in a few paragraphs’ time. So what does a Spool operator actually do? The spool operator consumes a set of data, and stores it in a temporary structure, in the tempdb database. This structure is typically either a Table (ie, a heap), or an Index (ie, a b-tree). If no data is actually needed from it, then it could also be a Row Count spool, which only stores the number of rows that the spool operator consumes. A Window Spool is another option if the data being consumed is tightly linked to windows of data, such as when the ROWS/RANGE clause of the OVER clause is being used. You could maybe think about the type of spool being like whether the cotton is going onto a small bobbin to fit in the base of the sewing machine, or whether it’s a larger spool for the top. A Table or Index Spool is either Eager or Lazy in nature. Eager and Lazy are Logical operators, which talk more about the behaviour, rather than the physical operation. If I’m sewing, I can either be all enthusiastic and get all my cotton onto the spool before I start, or I can do it as I need it. “Lazy” might not the be the best word to describe a person – in the SQL world it describes the idea of either fetching all the rows to build up the whole spool when the operator is called (Eager), or populating the spool only as it’s needed (Lazy). Window Spools are both physical and logical. They’re eager on a per-window basis, but lazy between windows. And when is it needed? The way I see it, spools are needed for two reasons. 1 – When data is going to be needed AGAIN. 2 – When data needs to be kept away from the original source. If you’re someone that writes long stored procedures, you are probably quite aware of the second scenario. I see plenty of stored procedures being written this way – where the query writer populates a temporary table, so that they can make updates to it without risking the original table. SQL does this too. Imagine I’m updating my contact list, and some of my changes move data to later in the book. If I’m not careful, I might update the same row a second time (or even enter an infinite loop, updating it over and over). A spool can make sure that I don’t, by using a copy of the data. This problem is known as the Halloween Effect (not because it’s spooky, but because it was discovered in late October one year). As I’m sure you can imagine, the kind of spool you’d need to protect against the Halloween Effect would be eager, because if you’re only handling one row at a time, then you’re not providing the protection... An eager spool will block the flow of data, waiting until it has fetched all the data before serving it up to the operator that called it. In the query below I’m forcing the Query Optimizer to use an index which would be upset if the Name column values got changed, and we see that before any data is fetched, a spool is created to load the data into. This doesn’t stop the index being maintained, but it does mean that the index is protected from the changes that are being done. There are plenty of times, though, when you need data repeatedly. Consider the query I put above. A simple join, but then counting the number of rows that came through. The way that this has executed (be it ideal or not), is to ask that a Table Spool be populated. That’s the Table Spool operator on the top row. That spool can produce the same set of rows repeatedly. This is the behaviour that we see in the bottom half of the plan. In the bottom half of the plan, we see that the a join is being done between the rows that are being sourced from the spool – one being aggregated and one not – producing the columns that we need for the query. Table v Index When considering whether to use a Table Spool or an Index Spool, the question that the Query Optimizer needs to answer is whether there is sufficient benefit to storing the data in a b-tree. The idea of having data in indexes is great, but of course there is a cost to maintaining them. Here we’re creating a temporary structure for data, and there is a cost associated with populating each row into its correct position according to a b-tree, as opposed to simply adding it to the end of the list of rows in a heap. Using a b-tree could even result in page-splits as the b-tree is populated, so there had better be a reason to use that kind of structure. That all depends on how the data is going to be used in other parts of the plan. If you’ve ever thought that you could use a temporary index for a particular query, well this is it – and the Query Optimizer can do that if it thinks it’s worthwhile. It’s worth noting that just because a Spool is populated using an Index Spool, it can still be fetched using a Table Spool. The details about whether or not a Spool used as a source shows as a Table Spool or an Index Spool is more about whether a Seek predicate is used, rather than on the underlying structure. Recursive CTE I’ve already shown you an example of spooling when the OVER clause is used. You might see them being used whenever you have data that is needed multiple times, and CTEs are quite common here. With the definition of a set of data described in a CTE, if the query writer is leveraging this by referring to the CTE multiple times, and there’s no simplification to be leveraged, a spool could theoretically be used to avoid reapplying the CTE’s logic. Annoyingly, this doesn’t happen. Consider this query, which really looks like it’s using the same data twice. I’m creating a set of data (which is completely deterministic, by the way), and then joining it back to itself. There seems to be no reason why it shouldn’t use a spool for the set described by the CTE, but it doesn’t. On the other hand, if we don’t pull as many columns back, we might see a very different plan. You see, CTEs, like all sub-queries, are simplified out to figure out the best way of executing the whole query. My example is somewhat contrived, and although there are plenty of cases when it’s nice to give the Query Optimizer hints about how to execute queries, it usually doesn’t do a bad job, even without spooling (and you can always use a temporary table). When recursion is used, though, spooling should be expected. Consider what we’re asking for in a recursive CTE. We’re telling the system to construct a set of data using an initial query, and then use set as a source for another query, piping this back into the same set and back around. It’s very much a spool. The analogy of cotton is long gone here, as the idea of having a continual loop of cotton feeding onto a spool and off again doesn’t quite fit, but that’s what we have here. Data is being fed onto the spool, and getting pulled out a second time when the spool is used as a source. (This query is running on AdventureWorks, which has a ManagerID column in HumanResources.Employee, not AdventureWorks2012) The Index Spool operator is sucking rows into it – lazily. It has to be lazy, because at the start, there’s only one row to be had. However, as rows get populated onto the spool, the Table Spool operator on the right can return rows when asked, ending up with more rows (potentially) getting back onto the spool, ready for the next round. (The Assert operator is merely checking to see if we’ve reached the MAXRECURSION point – it vanishes if you use OPTION (MAXRECURSION 0), which you can try yourself if you like). Spools are useful. Don’t lose sight of that. Every time you use temporary tables or table variables in a stored procedure, you’re essentially doing the same – don’t get upset at the Query Optimizer for doing so, even if you think the spool looks like an expensive part of the query. I hope you’re enjoying this T-SQL Tuesday. Why not head over to my post that is hosting it this month to read about some other plan operators? At some point I’ll write a summary post – once I have you should find a comment below pointing at it. @rob_farley

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