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  • MySQL Extremely High Disk Activity (Read Operations)

    - by Jake Schoermer
    I have 1GB Linode VPS with a standard LAMP stack. Apache is tuned fine but for some reason MySQL's disk usage is high. This is causing really slow site load times. RAM and CPU usage are fine. Can anyone give me any pointers on tuning mysql's disk performance? I'm using InnoDB. iotop output is below. Total DISK READ: 38.50 M/s | Total DISK WRITE: 27.20 K/s TID PRIO USER DISK READ> DISK WRITE SWAPIN IO COMMAND 9808 be/4 mysql 22.40 M/s 0.00 B/s 0.00 % 63.75 % mysqld 10045 be/4 mysql 2.06 M/s 0.00 B/s 0.00 % 26.65 % mysqld 9987 be/4 mysql 1694.38 K/s 0.00 B/s 0.00 % 18.33 % mysqld 10015 be/4 mysql 1554.47 K/s 0.00 B/s 0.00 % 12.71 % mysqld 10019 be/4 mysql 1461.21 K/s 0.00 B/s 0.00 % 5.58 % mysqld 9839 be/4 mysql 1383.48 K/s 0.00 B/s 0.00 % 25.69 % mysqld 10031 be/4 mysql 1243.58 K/s 0.00 B/s 0.00 % 5.68 % mysqld 10023 be/4 mysql 1057.04 K/s 0.00 B/s 0.00 % 2.02 % mysqld 10020 be/4 mysql 1025.95 K/s 0.00 B/s 0.00 % 7.05 % mysqld 10001 be/4 mysql 808.33 K/s 683.97 K/s 0.00 % 1.16 % mysqld 10025 be/4 mysql 746.15 K/s 0.00 B/s 0.00 % 3.28 % mysqld 10043 be/4 mysql 715.06 K/s 0.00 B/s 0.00 % 0.48 % mysqld 10044 be/4 mysql 672.31 K/s 0.00 B/s 0.00 % 5.25 % mysqld 10034 be/4 mysql 668.42 K/s 1989.73 K/s 0.00 % 5.31 % mysqld 9985 be/4 mysql 450.80 K/s 124.36 K/s 0.00 % 8.83 % mysqld 9989 be/4 mysql 357.53 K/s 0.00 B/s 0.00 % 5.21 % mysqld 10033 be/4 mysql 186.54 K/s 0.00 B/s 0.00 % 1.59 % mysqld 10021 be/4 mysql 155.45 K/s 435.25 K/s 0.00 % 1.23 % mysqld 10007 be/4 mysql 124.36 K/s 0.00 B/s 0.00 % 0.53 % mysqld 9763 be/4 www-data 38.86 K/s 0.00 B/s 0.00 % 4.56 % apache2 -k start 10027 be/4 mysql 31.09 K/s 0.00 B/s 0.00 % 4.24 % mysqld 1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % init 2 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthreadd] 3 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/0] 4 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/0:0] 5 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/u:0] 6 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/0] 7 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/1]

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  • warning: dict_ldap_lookup: Search error 1: Operations error

    - by drecute
    Please I need help with ldap search filter to use to retrieve the user email information from ldap. I'm running postfix_ldap of Ubuntu server 12.04. Everything seems to work fine, except getting the values returned from the search. Version 1 server_host = ldap://samba.example.com search_base = dc=company, dc=example, dc=com query_filter = mail=%s bind = no domain = example.com Version 2 server_host = ldap://samba.example.com search_base = dc=company, dc=example, dc=com query_filter = mail=%s bind_dn = cn=Users,dc=company,dc=example,dc=com domain = example.com mail logs Nov 26 11:13:26 mail postfix/smtpd[19662]: match_string: example.com ~? example.com Nov 26 11:13:26 mail postfix/smtpd[19662]: dict_ldap_lookup: No existing connection for LDAP source /etc/postfix/ldap-aliases.cf, reopening Nov 26 11:13:26 mail postfix/smtpd[19662]: dict_ldap_connect: Connecting to server ldap://samba.example.com Nov 26 11:13:26 mail postfix/smtpd[19662]: dict_ldap_connect: Actual Protocol version used is 3. Nov 26 11:13:26 mail postfix/smtpd[19662]: dict_ldap_connect: Binding to server ldap://samba.example.com with dn cn=Users,dc=company,dc=example,dc=com Nov 26 11:13:26 mail postfix/smtpd[19662]: warning: dict_ldap_connect: Unable to bind to server ldap://samba.example.com with dn cn=Users,dc=company,dc=example,dc=com: 49 (Invalid credentials) Nov 26 11:13:26 mail postfix/smtpd[19662]: warning: ldap:/etc/postfix/ldap-aliases.cf lookup error for "[email protected]" Nov 26 11:13:26 mail postfix/smtpd[19662]: maps_find: virtual_alias_maps: [email protected]: search aborted Nov 26 11:13:26 mail postfix/smtpd[19662]: mail_addr_find: [email protected] -> (try again) Nov 26 11:13:26 mail postfix/smtpd[19662]: NOQUEUE: reject: RCPT from col0-omc3-s2.col0.hotmail.com[65.55.34.140]: 451 4.3.0 <[email protected]>: Temporary lookup failure; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<col0-omc3-s2.col0.hotmail.com> Nov 26 11:13:26 mail postfix/smtpd[19662]: > col0-omc3-s2.col0.hotmail.com[65.55.34.140]: 451 4.3.0 <[email protected]>: Temporary lookup failure here's another log with successful search result but fialed to get the values of the result Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: Using existing connection for LDAP source /etc/postfix/ldap-aliases.cf Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: /etc/postfix/ldap-aliases.cf: Searching with filter [email protected] Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_get_values[1]: Search found 1 match(es) Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_get_values[1]: Leaving dict_ldap_get_values Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: Search returned nothing Nov 26 12:04:56 mail postfix/smtpd[20463]: maps_find: virtual_alias_maps: [email protected]: not found Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: In dict_ldap_lookup Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: /etc/postfix/ldap-aliases.cf: Skipping lookup of key 'tola.akintola': domain mismatch Nov 26 12:04:56 mail postfix/smtpd[20463]: maps_find: virtual_alias_maps: tola.akintola: not found Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: In dict_ldap_lookup Nov 26 12:04:56 mail postfix/smtpd[20463]: dict_ldap_lookup: /etc/postfix/ldap-aliases.cf: Skipping lookup of key '@example.com': domain mismatch Nov 26 12:04:56 mail postfix/smtpd[20463]: maps_find: virtual_alias_maps: @example.com: not found Nov 26 12:04:56 mail postfix/smtpd[20463]: mail_addr_find: [email protected] -> (not found) My refined ldap-aliases.cf looks like this: server_host = ldap://samba.example.com server_port = 3268 search_base = dc=company, dc=example, dc=com query_filter = mail=%s result_attribute = uid bind_dn = cn=Administrator,cn=Users,dc=company,dc=example,dc=com bind_pw = pass domain = example.com So I'll like to know what ldap filter is appropriate to get this to work. Thanks for helping out.

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  • Slow file operations, possible I/O error but chkdsk says OK

    - by mikolajek
    I've recently faced a strange problem. I use Directory Opus file manager that suddenly started to report an I/O error when trying to copy files onto one of my disks. The Windows Explorer did copy those files but it was extremely slow. I run chkdsk on this drive (ca. 300GB) and it took it over two days to complete! However it reported no errors found. I run Hard Disk Sentinel that says the drive is OK. But the files still read and write extremely slow! Can anyone advise me what to do? I have a spare space I am copying my files for backup now but should I get rid of this disk? Or can I try to "heal" it somehow? Many thanks for your ideas!

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  • Diagnosing extremely slow network operations.

    - by Chris Becke
    The network: * A windows 7 PC with 2 NICs - one connected to an old style ethernet hub - the other to the internet - with internet sharing enabled * An Apple iMac connected to the hub, successfully utilizing the ICS to access the internet. My problem: Using the Mac, copying from the internet is fast. However, if I connect to a SMB: share on the Windows 7 PC and try and copy anything a few kb the copy operation is appallingly slow with my network card using the Windows 7 control panel showing ~.1% utilization. The NICs are 100Mbs and show a 10x larger throughput (now ~1%) if I download large files over the internet using the Mac. WTF?

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  • Automated capturing of screen using "Microsoft Expression Encoder Screen Capture" command line operations

    - by gentlesea
    I want to capture screen output automatically from within my TestComplete test program. For this i found the free limited version of "Microsoft Expression Encoder Screen Capture" which I want to automate. Is there a separate command line interface for Microsoft Expression Encoder Screen Capture or do I have to use the command line interface for Expression Studio? I found this options: http://msdn.microsoft.com/en-us/library/cc294683.aspx. But before I dig deeper, I want to know if I am on the right way.

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  • My KDE very slow in certain operations

    - by Pietro
    I have a problem with my Linux installation. It seems that the KDE code that deals with directory windows is extremely slow (on both Dolphin and Konqueror). This happens both when I click on a directory icon and when I want to open/save a file from many KDE applications. The time the window takes to open can be one minute or more. The same happens when I right click on an icon. Looking at the CPU usage, this is very low (less than 10%). Am I the only one with this problem, or is it well known and maybe already fixed? Consider that I cannot update to a more recent version of OpenSuse. Thank you, Pietro Configuration: Linux version: OpenSuse 11.4 KDE 4.6.0 System: DELL Precision T3500 - Intel Xeon Home directory mounted on a remote drive. <-- could this be the reason?

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  • Good software to record desktop/screen operations [closed]

    - by juanmaflyer
    Possible Duplicate: What is the best software for desktop recording? Hi superuser's. I would like to record some tasks in a program (i want to make a video where i will be explaining how to use a particular program) and i haven't found a good software to do it yet... I have just tested camStudio but when i hit the Record Button the computer starts working very slowly (even when recording in a small area... so i wouldn't imagine how slow it will run if recording full screen). So i want you to recommend me some good software to record the screen on a fast way... Thanks a lot. Juan

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  • Boot to VHD backup plan

    - by Josh Barker
    I have a machine that I just reinstalled Windows and all of my applications onto... what a chore that is. I want to totally and completely avoid this from now on by creating an image. My first thought was to see if it possible to copy a VHD file when you are booted into it since I am using Windows 7 Ultimate as boot-to-vhd (without a parent machine). Is this possible and if so, how could I accomplish this? Keep in mind, this is my personal machine and I'm trying to keep things inexpensive (a good script would work). Thanks, Josh

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  • Logfile software for making querys, extracting and other operations

    - by Juw
    I have written an app that connects to a server IIS 6 to retrieve information. When doing this i have collected data (phone model etc) and send it to the server with a regular GET HTTP call like this: http://www.myserver.com/getData.php?phonemodel=userphone&appversion=2&id=20 This is logged in the IIS logfiles. I thought of writing my own parser for log files. But why invent the wheel? I´m looking for a software that can read the IIS 6 logfiles. I would like it to be able to do: Extraction - Extract all lines that contains: www.myserver.com/getData Filtering - View all lines where http-code is not 200 Queries - View all lines where phonemodel=iphone Any tips on free software that can help me with this? Thanx in advance!

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  • Clone a Red Hat RAID as part of a disaster recovery plan

    - by Campo
    I am looking for recommendations to clone a Red Hat mirrored raid to a single hard drive located in the same machine. The idea is if the servers hardware ever has an issue we have a similar hardware machine ready to go. All we would have to do is pop in the cloned drive. If the servers RAID ever failed we could just switch to the single drive to maintain uptime and restore the original configuration on the spare server with a backup. This is a restaurant and they are open 7 days a week. We do have time from 12:am to 9:00am to perform the necessary steps for a clone and we talking about under 10 Gigs of information. There is a database on the server. I have looked into Rsync and Clonezilla. But I am just not confident either is capable of completing the task I want. Looking for some suggestions and possibly a step by step if you could be so kind.

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  • Setting up IIS7 to mimic a GoDaddy shared hosting plan

    - by NerdFury
    I host multiple domains on a GoDaddy shared hosting account. I would like to setup a website locally in IIS 7 that mimics the setup of my hosted account so that I can test and debug applications locally before deploying, as debugging after deploying, or discovering there are issues after deploying is frustrating. I have created a folder WebRoot, at put my main application in that folder. I created a website in IIS 7 and pointed it at that folder. I setup bindings with a fake domain, and created a matching entry in my hosts file to make the fake domain point at my 127.0.0.1. I then created a folder www.otherdomain.com under webroot. I then created an application underneath my website, and pointed it at this folder. I can't find how I can add bindings to the web application to have it referenced as a different fake domain, rather than a subdirectory under my root domain. What would be the proper way to setup IIS to best simulate the environment on the GoDaddy servers.

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  • ESXi disaster recovery plan

    - by Marlin
    I have a Vmware infrastructure where I am using the free version of Esxi 5 . I cannot as a result use vmotion and the other cool features that come with a paid ESXI. I am using snapshots for the backups but they are stored on local hard drive. I need a better backup scenario where I can recover in the event of a harddrive failure. I tried openfiler but could not get it right. What backup method can I try given my situation?

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  • Encrypted directory makes file operations for whole disk very slow

    - by user1566277
    I am running an arm GNU/Linux and I have a SD-Card with three partitions on it. On one of the Partition I create an encfs file and then mount it on a directory which is in another partition to make that directory encrypted. Works fine. But now the writing speed on all the partitions are reduced drastically. I can understand that it should be slow for encrypted directory but why the its reducing write speed for all the partitions. E.g., if do not mount the encrypted directory 20MB is transferred in 2 Sec. roughly but with the encrypted directory mounted its like 20 Seconds for same file. I am using LUKS and all the partitons are ext3 except for the directory where /dev/mapper/encfs is mounted as type ext2. Any hints?

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  • Oracle Buys BigMachines - Adds Leading Configure, Price and Quote (CPQ) Cloud to the Oracle Cloud to Enable Smarter Selling

    - by Richard Lefebvre
    News Facts Oracle today announced that it has entered into an agreement to acquire BigMachines, a leading cloud-based Configure, Price and Quote (CPQ) solution provider. BigMachines’ CPQ Cloud accelerates the conversion of sales opportunities into revenue by automating the sales order process with guided selling, dynamic pricing, and an easy-to-use workflow approval process, accessible anywhere, on any device. Companies that use sales automation technology often rely on manual, cumbersome and disconnected processes to convert opportunities into orders. This creates errors, adds costs, delays revenue, and degrades the customer experience. BigMachines’ CPQ cloud extends sales automation to include the creation of an optimal quote, which enables sales personnel to easily configure and price complex products, select the best options, promotions and deal terms, and include up sell and renewals, all using automated workflows. In combination with Oracle’s enterprise-grade cloud solutions, including Marketing, Sales, Social, Commerce and Service Clouds, Oracle and BigMachines will create an end-to-end smarter selling cloud solution so sales personnel are more productive, customers are more satisfied, and companies grow revenue faster. More information on this announcement can be found at http://www.oracle.com/bigmachines Supporting Quotes “The fundamental goals of smarter selling are to provide sales teams with the information, access, and insights they need to maximize revenue opportunities and execute on all phases of the sales cycle,” said Thomas Kurian, Executive Vice President, Oracle Development. “By adding BigMachines’ CPQ Cloud to the Oracle Cloud, companies will be able to drive more revenue and increase customer satisfaction with a seamlessly integrated process across marketing and sales, pricing and quoting, and fulfillment and service.” “BigMachines has developed leading CPQ solutions that serve companies of all sizes across multiple industries,” said David Bonnette, BigMachines’ CEO. “Together with Oracle, we expect to provide a complete cloud solution to manage sales processes and deliver exceptional customer experiences.” Supporting Resources About Oracle and BigMachines General Presentation Customer and Partner Letter FAQ

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  • CSG operations on implicit surfaces with marching cubes [SOLVED]

    - by Mads Elvheim
    I render isosurfaces with marching cubes, (or perhaps marching squares as this is 2D) and I want to do set operations like set difference, intersection and union. I thought this was easy to implement, by simply choosing between two vertex scalars from two different implicit surfaces, but it is not. For my initial testing, I tried with two spheres circles, and the set operation difference. i.e A - B. One circle is moving and the other one is stationary. Here's the approach I tried when picking vertex scalars and when classifying corner vertices as inside or outside. The code is written in C++. OpenGL is used for rendering, but that's not important. Normal rendering without any CSG operations does give the expected result. void march(const vec2& cmin, //min x and y for the grid cell const vec2& cmax, //max x and y for the grid cell std::vector<vec2>& tri, float iso, float (*cmp1)(const vec2&), //distance from stationary circle float (*cmp2)(const vec2&) //distance from moving circle ) { unsigned int squareindex = 0; float scalar[4]; vec2 verts[8]; /* initial setup of the grid cell */ verts[0] = vec2(cmax.x, cmax.y); verts[2] = vec2(cmin.x, cmax.y); verts[4] = vec2(cmin.x, cmin.y); verts[6] = vec2(cmax.x, cmin.y); float s1,s2; /********************************** ********For-loop of interest****** *******Set difference between **** *******two implicit surfaces****** **********************************/ for(int i=0,j=0; i<4; ++i, j+=2){ s1 = cmp1(verts[j]); s2 = cmp2(verts[j]); if((s1 < iso)){ //if inside circle1 if((s2 < iso)){ //if inside circle2 scalar[i] = s2; //then set the scalar to the moving circle } else { scalar[i] = s1; //only inside circle1 squareindex |= (1<<i); //mark as inside } } else { scalar[i] = s1; //inside neither circle } } if(squareindex == 0) return; /* Usual interpolation between edge points to compute the new intersection points */ verts[1] = mix(iso, verts[0], verts[2], scalar[0], scalar[1]); verts[3] = mix(iso, verts[2], verts[4], scalar[1], scalar[2]); verts[5] = mix(iso, verts[4], verts[6], scalar[2], scalar[3]); verts[7] = mix(iso, verts[6], verts[0], scalar[3], scalar[0]); for(int i=0; i<10; ++i){ //10 = maxmimum 3 triangles, + one end token int index = triTable[squareindex][i]; //look up our indices for triangulation if(index == -1) break; tri.push_back(verts[index]); } } This gives me weird jaggies: It looks like the CSG operation is done without interpolation. It just "discards" the whole triangle. Do I need to interpolate in some other way, or combine the vertex scalar values? I'd love some help with this. A full testcase can be downloaded HERE EDIT: Basically, my implementation of marching squares works fine. It is my scalar field which is broken, and I wonder what the correct way would look like. Preferably I'm looking for a general approach to implement the three set operations I discussed above, for the usual primitives (circle, rectangle/square, plane)

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  • Hello Operator, My Switch Is Bored

    - by Paul White
    This is a post for T-SQL Tuesday #43 hosted by my good friend Rob Farley. The topic this month is Plan Operators. I haven’t taken part in T-SQL Tuesday before, but I do like to write about execution plans, so this seemed like a good time to start. This post is in two parts. The first part is primarily an excuse to use a pretty bad play on words in the title of this blog post (if you’re too young to know what a telephone operator or a switchboard is, I hate you). The second part of the post looks at an invisible query plan operator (so to speak). 1. My Switch Is Bored Allow me to present the rare and interesting execution plan operator, Switch: Books Online has this to say about Switch: Following that description, I had a go at producing a Fast Forward Cursor plan that used the TOP operator, but had no luck. That may be due to my lack of skill with cursors, I’m not too sure. The only application of Switch in SQL Server 2012 that I am familiar with requires a local partitioned view: CREATE TABLE dbo.T1 (c1 int NOT NULL CHECK (c1 BETWEEN 00 AND 24)); CREATE TABLE dbo.T2 (c1 int NOT NULL CHECK (c1 BETWEEN 25 AND 49)); CREATE TABLE dbo.T3 (c1 int NOT NULL CHECK (c1 BETWEEN 50 AND 74)); CREATE TABLE dbo.T4 (c1 int NOT NULL CHECK (c1 BETWEEN 75 AND 99)); GO CREATE VIEW V1 AS SELECT c1 FROM dbo.T1 UNION ALL SELECT c1 FROM dbo.T2 UNION ALL SELECT c1 FROM dbo.T3 UNION ALL SELECT c1 FROM dbo.T4; Not only that, but it needs an updatable local partitioned view. We’ll need some primary keys to meet that requirement: ALTER TABLE dbo.T1 ADD CONSTRAINT PK_T1 PRIMARY KEY (c1);   ALTER TABLE dbo.T2 ADD CONSTRAINT PK_T2 PRIMARY KEY (c1);   ALTER TABLE dbo.T3 ADD CONSTRAINT PK_T3 PRIMARY KEY (c1);   ALTER TABLE dbo.T4 ADD CONSTRAINT PK_T4 PRIMARY KEY (c1); We also need an INSERT statement that references the view. Even more specifically, to see a Switch operator, we need to perform a single-row insert (multi-row inserts use a different plan shape): INSERT dbo.V1 (c1) VALUES (1); And now…the execution plan: The Constant Scan manufactures a single row with no columns. The Compute Scalar works out which partition of the view the new value should go in. The Assert checks that the computed partition number is not null (if it is, an error is returned). The Nested Loops Join executes exactly once, with the partition id as an outer reference (correlated parameter). The Switch operator checks the value of the parameter and executes the corresponding input only. If the partition id is 0, the uppermost Clustered Index Insert is executed, adding a row to table T1. If the partition id is 1, the next lower Clustered Index Insert is executed, adding a row to table T2…and so on. In case you were wondering, here’s a query and execution plan for a multi-row insert to the view: INSERT dbo.V1 (c1) VALUES (1), (2); Yuck! An Eager Table Spool and four Filters! I prefer the Switch plan. My guess is that almost all the old strategies that used a Switch operator have been replaced over time, using things like a regular Concatenation Union All combined with Start-Up Filters on its inputs. Other new (relative to the Switch operator) features like table partitioning have specific execution plan support that doesn’t need the Switch operator either. This feels like a bit of a shame, but perhaps it is just nostalgia on my part, it’s hard to know. Please do let me know if you encounter a query that can still use the Switch operator in 2012 – it must be very bored if this is the only possible modern usage! 2. Invisible Plan Operators The second part of this post uses an example based on a question Dave Ballantyne asked using the SQL Sentry Plan Explorer plan upload facility. If you haven’t tried that yet, make sure you’re on the latest version of the (free) Plan Explorer software, and then click the Post to SQLPerformance.com button. That will create a site question with the query plan attached (which can be anonymized if the plan contains sensitive information). Aaron Bertrand and I keep a close eye on questions there, so if you have ever wanted to ask a query plan question of either of us, that’s a good way to do it. The problem The issue I want to talk about revolves around a query issued against a calendar table. The script below creates a simplified version and adds 100 years of per-day information to it: USE tempdb; GO CREATE TABLE dbo.Calendar ( dt date NOT NULL, isWeekday bit NOT NULL, theYear smallint NOT NULL,   CONSTRAINT PK__dbo_Calendar_dt PRIMARY KEY CLUSTERED (dt) ); GO -- Monday is the first day of the week for me SET DATEFIRST 1;   -- Add 100 years of data INSERT dbo.Calendar WITH (TABLOCKX) (dt, isWeekday, theYear) SELECT CA.dt, isWeekday = CASE WHEN DATEPART(WEEKDAY, CA.dt) IN (6, 7) THEN 0 ELSE 1 END, theYear = YEAR(CA.dt) FROM Sandpit.dbo.Numbers AS N CROSS APPLY ( VALUES (DATEADD(DAY, N.n - 1, CONVERT(date, '01 Jan 2000', 113))) ) AS CA (dt) WHERE N.n BETWEEN 1 AND 36525; The following query counts the number of weekend days in 2013: SELECT Days = COUNT_BIG(*) FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; It returns the correct result (104) using the following execution plan: The query optimizer has managed to estimate the number of rows returned from the table exactly, based purely on the default statistics created separately on the two columns referenced in the query’s WHERE clause. (Well, almost exactly, the unrounded estimate is 104.289 rows.) There is already an invisible operator in this query plan – a Filter operator used to apply the WHERE clause predicates. We can see it by re-running the query with the enormously useful (but undocumented) trace flag 9130 enabled: Now we can see the full picture. The whole table is scanned, returning all 36,525 rows, before the Filter narrows that down to just the 104 we want. Without the trace flag, the Filter is incorporated in the Clustered Index Scan as a residual predicate. It is a little bit more efficient than using a separate operator, but residual predicates are still something you will want to avoid where possible. The estimates are still spot on though: Anyway, looking to improve the performance of this query, Dave added the following filtered index to the Calendar table: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear) WHERE isWeekday = 0; The original query now produces a much more efficient plan: Unfortunately, the estimated number of rows produced by the seek is now wrong (365 instead of 104): What’s going on? The estimate was spot on before we added the index! Explanation You might want to grab a coffee for this bit. Using another trace flag or two (8606 and 8612) we can see that the cardinality estimates were exactly right initially: The highlighted information shows the initial cardinality estimates for the base table (36,525 rows), the result of applying the two relational selects in our WHERE clause (104 rows), and after performing the COUNT_BIG(*) group by aggregate (1 row). All of these are correct, but that was before cost-based optimization got involved :) Cost-based optimization When cost-based optimization starts up, the logical tree above is copied into a structure (the ‘memo’) that has one group per logical operation (roughly speaking). The logical read of the base table (LogOp_Get) ends up in group 7; the two predicates (LogOp_Select) end up in group 8 (with the details of the selections in subgroups 0-6). These two groups still have the correct cardinalities as trace flag 8608 output (initial memo contents) shows: During cost-based optimization, a rule called SelToIdxStrategy runs on group 8. It’s job is to match logical selections to indexable expressions (SARGs). It successfully matches the selections (theYear = 2013, is Weekday = 0) to the filtered index, and writes a new alternative into the memo structure. The new alternative is entered into group 8 as option 1 (option 0 was the original LogOp_Select): The new alternative is to do nothing (PhyOp_NOP = no operation), but to instead follow the new logical instructions listed below the NOP. The LogOp_GetIdx (full read of an index) goes into group 21, and the LogOp_SelectIdx (selection on an index) is placed in group 22, operating on the result of group 21. The definition of the comparison ‘the Year = 2013’ (ScaOp_Comp downwards) was already present in the memo starting at group 2, so no new memo groups are created for that. New Cardinality Estimates The new memo groups require two new cardinality estimates to be derived. First, LogOp_Idx (full read of the index) gets a predicted cardinality of 10,436. This number comes from the filtered index statistics: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH STAT_HEADER; The second new cardinality derivation is for the LogOp_SelectIdx applying the predicate (theYear = 2013). To get a number for this, the cardinality estimator uses statistics for the column ‘theYear’, producing an estimate of 365 rows (there are 365 days in 2013!): DBCC SHOW_STATISTICS (Calendar, theYear) WITH HISTOGRAM; This is where the mistake happens. Cardinality estimation should have used the filtered index statistics here, to get an estimate of 104 rows: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH HISTOGRAM; Unfortunately, the logic has lost sight of the link between the read of the filtered index (LogOp_GetIdx) in group 22, and the selection on that index (LogOp_SelectIdx) that it is deriving a cardinality estimate for, in group 21. The correct cardinality estimate (104 rows) is still present in the memo, attached to group 8, but that group now has a PhyOp_NOP implementation. Skipping over the rest of cost-based optimization (in a belated attempt at brevity) we can see the optimizer’s final output using trace flag 8607: This output shows the (incorrect, but understandable) 365 row estimate for the index range operation, and the correct 104 estimate still attached to its PhyOp_NOP. This tree still has to go through a few post-optimizer rewrites and ‘copy out’ from the memo structure into a tree suitable for the execution engine. One step in this process removes PhyOp_NOP, discarding its 104-row cardinality estimate as it does so. To finish this section on a more positive note, consider what happens if we add an OVER clause to the query aggregate. This isn’t intended to be a ‘fix’ of any sort, I just want to show you that the 104 estimate can survive and be used if later cardinality estimation needs it: SELECT Days = COUNT_BIG(*) OVER () FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; The estimated execution plan is: Note the 365 estimate at the Index Seek, but the 104 lives again at the Segment! We can imagine the lost predicate ‘isWeekday = 0’ as sitting between the seek and the segment in an invisible Filter operator that drops the estimate from 365 to 104. Even though the NOP group is removed after optimization (so we don’t see it in the execution plan) bear in mind that all cost-based choices were made with the 104-row memo group present, so although things look a bit odd, it shouldn’t affect the optimizer’s plan selection. I should also mention that we can work around the estimation issue by including the index’s filtering columns in the index key: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear, isWeekday) WHERE isWeekday = 0 WITH (DROP_EXISTING = ON); There are some downsides to doing this, including that changes to the isWeekday column may now require Halloween Protection, but that is unlikely to be a big problem for a static calendar table ;)  With the updated index in place, the original query produces an execution plan with the correct cardinality estimation showing at the Index Seek: That’s all for today, remember to let me know about any Switch plans you come across on a modern instance of SQL Server! Finally, here are some other posts of mine that cover other plan operators: Segment and Sequence Project Common Subexpression Spools Why Plan Operators Run Backwards Row Goals and the Top Operator Hash Match Flow Distinct Top N Sort Index Spools and Page Splits Singleton and Range Seeks Bitmaps Hash Join Performance Compute Scalar © 2013 Paul White – All Rights Reserved Twitter: @SQL_Kiwi

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  • Manipulating matrix operations (transpose, negation, addition, and mutiplication) using functions in

    - by user292489
    I was trying to manipulate matrices in my input file using functions. My input file is: A 3 3 1 2 3 4 5 6 7 8 9 B 3 3 1 0 0 0 1 0 0 0 1 C 2 3 3 5 8 -1 -2 -3 D 3 5 0 0 0 1 0 1 0 1 0 1 0 1 0 0 1 E 1 1 10 F 3 10 1 0 2 0 3 0 4 0 5 0 0 2 3 -1 -3 -4 -3 8 3 7 0 0 0 4 6 5 8 2 -1 10 I am having trouble in implementing the functions that I declared. I assumed my program will perform those operations: transpose, negate, add, and multiply matices according to the users choice: /* once this program is compiled and executed, it will perform the basic matrix * operations: negation, transpose, addition, and multiplication. */ #include <stdio.h> #include <stdlib.h> #define MAX 10 int readmatrix(FILE *input, char martixname[6],int , mat[10][10], int i, int j); void printmatrix(char matrixname[6], int mat[10][10], int i, int j); void Negate(char matrixname[6], int mat[10][10], int i, int j); void add(char matrixname[6], int mat[10][10],int i, int k); void multiply(char matrixname[], int mat[][10], char A[], int i, int k); void transpose (char matrixname[], int mat[][10], char A[], int); void printT(int mat[][10], int); int selctoption(); char selectmatrix(); int main(int argc, char *argv[]) { char matrixtype[6]; int mat[][10]; FILE *filein; int size; int optionop; int matrixop; int option; if (argc != 2) { printf("Usage: executable input.\n"); exit(0); } filein = fopen(argv[1], "r"); if (!filein) { printf("ERROR: input file not found.\n"); exit (0); } size = readmatrix (filein, matrixtype); printmatrix(matrix[][10], size); option = selectoption(); matrixtype = selectmatrix(); //printf("You have: %5.2f ", deposit); optionop = readmatrix(option, matrix[][10], size); if (choiceop == 6) { printf("Thanks for using the matrix operation program.\n"); exit(0); } printf("Please select from the following matrix operations:\n") printf("\t1. Print matrix\n"); printf("\t2. Negate matrix\n"); printf("\t3. Transpose matrix\n"); printf("\t4. Add matrices\n"); printf("\t5. Multiply matrices\n"); printf("\t6. Quit\n"); fclose(filein); return 0; } do { printf("Please select option(1-%d):", optionop); scanf("%d", &matrixop); } while(matrixop <= 0 || matrixop > optionop); void readmatrix (FILE *in, int mat[][10], char A[], int i, int j) { int i=0,j = 0; while (fscanf(in, "%d", &mat[i][j]) != EOF) return 0; } // I would appreciate anyone's feedback.

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  • Is it possible to implement bitwise operators using integer arithmetic?

    - by Statement
    Hello World! I am facing a rather peculiar problem. I am working on a compiler for an architecture that doesn't support bitwise operations. However, it handles signed 16 bit integer arithmetics and I was wondering if it would be possible to implement bitwise operations using only: Addition (c = a + b) Subtraction (c = a - b) Division (c = a / b) Multiplication (c = a * b) Modulus (c = a % b) Minimum (c = min(a, b)) Maximum (c = max(a, b)) Comparisons (c = (a < b), c = (a == b), c = (a <= b), et.c.) Jumps (goto, for, et.c.) The bitwise operations I want to be able to support are: Or (c = a | b) And (c = a & b) Xor (c = a ^ b) Left Shift (c = a << b) Right Shift (c = a b) (All integers are signed so this is a problem) Signed Shift (c = a b) One's Complement (a = ~b) (Already found a solution, see below) Normally the problem is the other way around; how to achieve arithmetic optimizations using bitwise hacks. However not in this case. Writable memory is very scarce on this architecture, hence the need for bitwise operations. The bitwise functions themselves should not use a lot of temporary variables. However, constant read-only data & instruction memory is abundant. A side note here also is that jumps and branches are not expensive and all data is readily cached. Jumps cost half the cycles as arithmetic (including load/store) instructions do. On other words, all of the above supported functions cost twice the cycles of a single jump. Some thoughts that might help: I figured out that you can do one's complement (negate bits) with the following code: // Bitwise one's complement b = ~a; // Arithmetic one's complement b = -1 - a; I also remember the old shift hack when dividing with a power of two so the bitwise shift can be expressed as: // Bitwise left shift b = a << 4; // Arithmetic left shift b = a * 16; // 2^4 = 16 // Signed right shift b = a >>> 4; // Arithmetic right shift b = a / 16; For the rest of the bitwise operations I am slightly clueless. I wish the architects of this architecture would have supplied bit-operations. I would also like to know if there is a fast/easy way of computing the power of two (for shift operations) without using a memory data table. A naive solution would be to jump into a field of multiplications: b = 1; switch (a) { case 15: b = b * 2; case 14: b = b * 2; // ... exploting fallthrough (instruction memory is magnitudes larger) case 2: b = b * 2; case 1: b = b * 2; } Or a Set & Jump approach: switch (a) { case 15: b = 32768; break; case 14: b = 16384; break; // ... exploiting the fact that a jump is faster than one additional mul // at the cost of doubling the instruction memory footprint. case 2: b = 4; break; case 1: b = 2; break; }

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  • 48-bit bitwise operations in Javascript?

    - by randomhelp
    I've been given the task of porting Java's Java.util.Random() to JavaScript, and I've run across a huge performance hit/inaccuracy using bitwise operators in Javascript on sufficiently large numbers. Some cursory research states that "bitwise operators in JavaScript are inherently slow," because internally it appears that JavaScript will cast all of its double values into signed 32-bit integers to do the bitwise operations (see https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Operators/Bitwise_Operators for more on this.) Because of this, I can't do a direct port of the Java random number generator, and I need to get the same numeric results as Java.util.Random(). Writing something like this.next = function(bits) { if (!bits) { bits = 48; } this.seed = (this.seed * 25214903917 + 11) & ((1 << 48) - 1); return this.seed >>> (48 - bits); }; (which is an almost-direct port of the Java.util.Random()) code won't work properly, since Javascript can't do bitwise operations on an integer that size.) I've figured out that I can just make a seedable random number generator in 32-bit space using the Lehmer algorithm, but the trick is that I need to get the same values as I would with Java.util.Random(). What should I do to make a faster, functional port?

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