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  • Error while mounting home directory on different logical volume

    - by RCola
    I created RAID 5 form 3 hard drives. Formatted as ext4 this raid array. Created VG0 group and lv_home logical volume in LVM. Then I tried to mount default /home directory on lv_home, while trying to mount logical volume lv_home to folder containing user profiles /home, getting error: mount: wrong fs type, bad option, bad superblock on /dev/mapper/VG0-lv_home next is seems to be symbolic link: # file -s /dev/VG0/lv_home /dev/VG0/lv_home: symbolic link to `../mapper/VG0-lv_home' then # file -s /dev/mapper/VG0-lv_home /dev/mapper/VG0-lv_home: data and lvm> pvs PV VG Fmt Attr PSize PFree /dev/md0 VG0 lvm2 a- 2.02g 68.00m lvm> lvdisplay --- Logical volume --- LV Name /dev/VG0/lv_home VG Name VG0 LV UUID WzJus7-2yV8-yhog-Ju1b-TpWH-IIAI-LIutwe LV Write Access read/write LV Status available # open 0 LV Size 1.17 GiB Current LE 300 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 251:0

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  • How to automatically display relationships in logical diagram?

    - by Cliff Chaney
    Consider a Logical Model where Entity A and Entity B are connected via Relationship Z. If I create a Logical Diagram (note: not another logical MODEL), I am able to drag Entity A and Entity B onto the diagram. Since the Logical Model already "knows" that Entity A and Entity B have a relationship, I would like to be able to easily add it to my logical diagram. I am already aware of the "Show Symbols" option whereby I can select the specific relationship that I want and have it appear. That is not a solution for me. The problem is that I have a LARGE logical model consisting of HUNDREDS of Entities and their various relationships. I then need to create application-specific diagrams consisting of a subset of those entities. I can easily identify and drag the 50+ entities onto a new diagram. But identifying and selecting all the associations is an exercise in frustration. Is there an option or some sort of feature that I'm missing - or any other trick - that would allow me to add only the relationships between selected entities or all entities on a diagram?

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  • How to paste text and variables into a logical expression in R?

    - by Jasper
    I want to paste variables in the logical expression that I am using to subset data, but the subset function does not see them as column names when pasted (either with ot without quotes). I have a dataframe with columns named col1, col2 etc. I want to subset for the rows in which colx < 0.05 This DOES work: subsetdata<-subset(dataframe, col1<0.05) subsetdata<-subset(dataframe, col2<0.05) This does NOT work: for (k in 1:2){ subsetdata<-subset(dataframe, paste("col",k,sep="")<0.05) } for (k in 1:2){ subsetdata<-subset(dataframe, noquote(paste("col",k,sep=""))<0.05) } I can't find the answer; any suggestions?

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  • Cloud Computing - Multiple Physical Computers, One Logical Computer

    - by Koobz
    I know that you can set up multiple virtual machines per physical computer. I'm wondering if it's possible to make multiple physical computers behave as one logical unit? Fundamentally the way I imagine it working is that you can throw 10 computers into a facility one day. You've got one client that requires the equivalent of two computers worth, and 100 others that eat up the remaining 8. As demands change you're just reallocating logical resources, maybe the 2 computer client now requires a third physical system. You just add it to the cloud, and don't worry about sharding the database, or migrating data over to a new server. Can it work this way? If yes, why would anyone ever do things like partition their database servers anymore? Just add more computing resources. You scale horizontally with the hardware, but your server appears to scale vertically. There's no need to modify your application's infrastructure to support multiple databases etc.

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  • Cloud Computing - Multiple Physical Computers, One Logical Computer

    - by bundini
    I know that you can set up multiple virtual machines per physical computer. I'm wondering if it's possible to make multiple physical computers behave as one logical unit? Fundamentally the way I imagine it working is that you can throw 10 computers into a facility one day. You've got one client that requires the equivalent of two computers worth, and 100 others that eat up the remaining 8. As demands change you're just reallocating logical resources, maybe the 2 computer client now requires a third physical system. You just add it to the cloud, and don't worry about sharding the database, or migrating data over to a new server. Can it work this way? If yes, why would anyone ever do things like hand partition their database servers anymore? Just add more computing resources. You scale horizontally with the hardware, but your server appears to scale vertically. There's no need to modify your application's supporting infrastructure to support multiple databases etc.

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  • Changing default logical filename in SQL 2005

    - by Andrew
    I have a issue about creating databases in SQL 2005. I want to be able to change the default logical filename for the mdf file. At the moment the log logical filename ends in _log by default. I want the data logical filename to automatically end with _data for consistency. Is there a way i can set this? Andrew

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  • User reduced LVM logical volume without resizing filesystem

    - by Matthew
    I received an email yesterday that one of our users was trying to make room for a heartbeat/clustering package which requires its own partition to act as a voting disk. To do this, he attempted to reduce the size of the root partition's logical volume, and then create a new logical volume for this purpose. However, he forgot to resize the filesystem first (or include the -r switch in the command). He also forgot to unmount the root partition by running this process from a rescue cd. The system is now refusing to boot into the OS with the following error: Either the superblock or the partition table is likely to be corrupt! Unexpected Inconsistency; run fsck manually. The system them drops the user into single user mode. Is it possible to rescue the filesystem, or is it hosed? Its running ext3.

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  • "reduce" or "apply" using logical functions in Clojure

    - by Alex B
    I cannot use logical functions on a range of booleans in Clojure (1.2). Neither of the following works due to logical functions being macros: (reduce and [... sequence of bools ...]) (apply or [... sequence of bools ...]) The error saying that I "can't take value of a macro: #'clojure.core/and". How to apply these logical functions (macros) without writing boilerplate code?

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  • How to recover logical volume deleted with lvremove

    - by John P
    I am on CentOS 5.5 and am running Xen. I have a large volume group that I create logical volumes on using lvcreate. Today I had a customer cancel her account, then change her mind about an hour later. Unfortunately I had already removed the LVM her Xen image resided on. (just using a standard lvremove ). There has been no other LVM activity on this disk since then (nothing else added or deleted). Is it possible to "undo" a lvremove, or recover logical volume? If so, how would I go about it?

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  • Is there a Generic USB TouchScreen Driver 12.04?

    - by lbjoum
    Is there a Generic USB TouchScreen Driver 12.04? Device 03eb:201c I've been looking for 4 days solid (not very skilled) and can't find a solution. I have a generic tablet: C97- Atom N2600 9.7" 2GB 32GB Bluetooth WiFi WebCam Ext.3G Windows 7 Tablet PC Using 12.04 and cannot find a driver. I installed android and the touchscreen works but still lots of other bugs. Oh well, stuck with Windows 7 and not happy about it. Will keep trying, but too much time wasted already. If you have a solution I would love to try it. ubuntu@ubuntu:~$ lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 001 Device 002: ID 0cf2:6238 ENE Technology, Inc. Bus 001 Device 003: ID 1a40:0101 Terminus Technology Inc. 4-Port HUB Bus 001 Device 005: ID 05e1:0100 Syntek Semiconductor Co., Ltd 802.11g + Bluetooth Wireless Adapter Bus 001 Device 006: ID 090c:3731 Silicon Motion, Inc. - Taiwan (formerly Feiya Technology Corp.) Bus 003 Device 002: ID 03eb:201c Atmel Corp. at90usbkey sample firmware (HID mouse) (from Windows: HID\VID_03EB&PID_201C\6&5F38127&0&0000 USB\VID_03EB&PID_201C\5&193ADADC&1&2 ) Bus 001 Device 007: ID 0518:0001 EzKEY Corp. USB to PS2 Adaptor v1.09 Bus 001 Device 008: ID 192f:0916 Avago Technologies, Pte. ubuntu@ubuntu:~$ sudo lsusb -v Bus 003 Device 002: ID 03eb:201c Atmel Corp. at90usbkey sample firmware (HID mouse) Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 32 idVendor 0x03eb Atmel Corp. idProduct 0x201c at90usbkey sample firmware (HID mouse) bcdDevice 45.a2 iManufacturer 1 CDT iProduct 2 9.75 iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 34 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x00 (Missing must-be-set bit!) (Bus Powered) MaxPower 100mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 3 Human Interface Device bInterfaceSubClass 0 No Subclass bInterfaceProtocol 0 None iInterface 0 HID Device Descriptor: bLength 9 bDescriptorType 33 bcdHID 1.11 bCountryCode 0 Not supported bNumDescriptors 1 bDescriptorType 34 Report wDescriptorLength 177 Report Descriptors: ** UNAVAILABLE ** Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 5 Device Status: 0x00fb Self Powered Remote Wakeup Enabled Debug Mode ubuntu@ubuntu:~$ sudo lshw ubuntu description: Notebook product: To be filled by O.E.M. (To be filled by O.E.M.) vendor: To be filled by O.E.M. version: To be filled by O.E.M. serial: To be filled by O.E.M. width: 32 bits capabilities: smbios-2.7 dmi-2.7 smp-1.4 smp configuration: boot=normal chassis=notebook cpus=2 family=To be filled by O.E.M. sku=To be filled by O.E.M. uuid=00020003-0004-0005-0006-000700080009 *-core description: Motherboard product: Tiger Hill vendor: INTEL Corporation physical id: 0 version: To be filled by O.E.M. serial: To be filled by O.E.M. slot: To be filled by O.E.M. *-firmware description: BIOS vendor: American Megatrends Inc. physical id: 0 version: 4.6.5 date: 08/24/2012 size: 64KiB capacity: 960KiB capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer acpi usb biosbootspecification *-cpu:0 description: CPU product: Intel(R) Atom(TM) CPU N2600 @ 1.60GHz vendor: Intel Corp. physical id: 4 bus info: cpu@0 version: 6.6.1 serial: 0003-0661-0000-0000-0000-0000 slot: CPU 1 size: 1600MHz capacity: 1600MHz width: 64 bits clock: 400MHz capabilities: x86-64 boot fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx constant_tsc arch_perfmon pebs bts nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm arat configuration: cores=2 enabledcores=1 id=2 threads=2 *-cache:0 description: L1 cache physical id: 5 slot: L1-Cache size: 24KiB capacity: 24KiB capabilities: internal write-back unified *-cache:1 description: L2 cache physical id: 6 slot: L2-Cache size: 512KiB capacity: 512KiB capabilities: internal varies unified *-logicalcpu:0 description: Logical CPU physical id: 2.1 width: 64 bits capabilities: logical *-logicalcpu:1 description: Logical CPU physical id: 2.2 width: 64 bits capabilities: logical *-logicalcpu:2 description: Logical CPU physical id: 2.3 width: 64 bits capabilities: logical *-logicalcpu:3 description: Logical CPU physical id: 2.4 width: 64 bits capabilities: logical *-memory description: System Memory physical id: 28 slot: System board or motherboard size: 2GiB *-bank:0 description: SODIMM [empty] product: [Empty] vendor: [Empty] physical id: 0 serial: [Empty] slot: DIMM0 *-bank:1 description: SODIMM DDR3 Synchronous 800 MHz (1.2 ns) vendor: 69 physical id: 1 serial: 00000210 slot: DIMM1 size: 2GiB width: 64 bits clock: 800MHz (1.2ns) *-cpu:1 physical id: 1 bus info: cpu@1 version: 6.6.1 serial: 0003-0661-0000-0000-0000-0000 size: 1600MHz capabilities: ht configuration: id=2 *-logicalcpu:0 description: Logical CPU physical id: 2.1 capabilities: logical *-logicalcpu:1 description: Logical CPU physical id: 2.2 capabilities: logical *-logicalcpu:2 description: Logical CPU physical id: 2.3 capabilities: logical *-logicalcpu:3 description: Logical CPU physical id: 2.4 capabilities: logical *-pci description: Host bridge product: Atom Processor D2xxx/N2xxx DRAM Controller vendor: Intel Corporation physical id: 100 bus info: pci@0000:00:00.0 version: 03 width: 32 bits clock: 33MHz *-display UNCLAIMED description: VGA compatible controller product: Atom Processor D2xxx/N2xxx Integrated Graphics Controller vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 09 width: 32 bits clock: 33MHz capabilities: pm msi vga_controller bus_master cap_list configuration: latency=0 resources: memory:dfe00000-dfefffff ioport:f100(size=8) *-multimedia description: Audio device product: N10/ICH 7 Family High Definition Audio Controller vendor: Intel Corporation physical id: 1b bus info: pci@0000:00:1b.0 version: 02 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: driver=snd_hda_intel latency=0 resources: irq:42 memory:dff00000-dff03fff *-pci:0 description: PCI bridge product: N10/ICH 7 Family PCI Express Port 1 vendor: Intel Corporation physical id: 1c bus info: pci@0000:00:1c.0 version: 02 width: 32 bits clock: 33MHz capabilities: pci pciexpress msi pm normal_decode bus_master cap_list configuration: driver=pcieport resources: irq:40 ioport:2000(size=4096) memory:80000000-801fffff ioport:80200000(size=2097152) *-usb:0 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #1 vendor: Intel Corporation physical id: 1d bus info: pci@0000:00:1d.0 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:23 ioport:f0a0(size=32) *-usb:1 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #2 vendor: Intel Corporation physical id: 1d.1 bus info: pci@0000:00:1d.1 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:19 ioport:f080(size=32) *-usb:2 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #3 vendor: Intel Corporation physical id: 1d.2 bus info: pci@0000:00:1d.2 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:18 ioport:f060(size=32) *-usb:3 description: USB controller product: N10/ICH 7 Family USB UHCI Controller #4 vendor: Intel Corporation physical id: 1d.3 bus info: pci@0000:00:1d.3 version: 02 width: 32 bits clock: 33MHz capabilities: uhci bus_master configuration: driver=uhci_hcd latency=0 resources: irq:16 ioport:f040(size=32) *-usb:4 description: USB controller product: N10/ICH 7 Family USB2 EHCI Controller vendor: Intel Corporation physical id: 1d.7 bus info: pci@0000:00:1d.7 version: 02 width: 32 bits clock: 33MHz capabilities: pm debug ehci bus_master cap_list configuration: driver=ehci_hcd latency=0 resources: irq:23 memory:dff05000-dff053ff *-pci:1 description: PCI bridge product: 82801 Mobile PCI Bridge vendor: Intel Corporation physical id: 1e bus info: pci@0000:00:1e.0 version: e2 width: 32 bits clock: 33MHz capabilities: pci subtractive_decode bus_master cap_list *-isa description: ISA bridge product: NM10 Family LPC Controller vendor: Intel Corporation physical id: 1f bus info: pci@0000:00:1f.0 version: 02 width: 32 bits clock: 33MHz capabilities: isa bus_master cap_list configuration: latency=0 *-storage description: SATA controller product: N10/ICH7 Family SATA Controller [AHCI mode] vendor: Intel Corporation physical id: 1f.2 bus info: pci@0000:00:1f.2 logical name: scsi0 version: 02 width: 32 bits clock: 66MHz capabilities: storage msi pm ahci_1.0 bus_master cap_list emulated configuration: driver=ahci latency=0 resources: irq:41 ioport:f0f0(size=8) ioport:f0e0(size=4) ioport:f0d0(size=8) ioport:f0c0(size=4) ioport:f020(size=16) memory:dff04000-dff043ff *-disk description: ATA Disk product: BIWIN SSD physical id: 0.0.0 bus info: scsi@0:0.0.0 logical name: /dev/sda version: 1206 serial: 123403501060 size: 29GiB (32GB) capabilities: partitioned partitioned:dos configuration: ansiversion=5 signature=8fbe402b *-volume:0 description: Windows NTFS volume physical id: 1 bus info: scsi@0:0.0.0,1 logical name: /dev/sda1 version: 3.1 serial: 249bde5d-8246-9a40-88c7-2d5e3bcaf692 size: 19GiB capacity: 19GiB capabilities: primary bootable ntfs initialized configuration: clustersize=4096 created=2011-04-04 02:27:51 filesystem=ntfs state=clean *-volume:1 description: Windows NTFS volume physical id: 2 bus info: scsi@0:0.0.0,2 logical name: /dev/sda2 version: 3.1 serial: de12d40f-d5ca-8642-b306-acd9349fda1a size: 10231MiB capacity: 10GiB capabilities: primary ntfs initialized configuration: clustersize=4096 created=2011-04-04 01:52:26 filesystem=ntfs state=clean *-serial UNCLAIMED description: SMBus product: N10/ICH 7 Family SMBus Controller vendor: Intel Corporation physical id: 1f.3 bus info: pci@0000:00:1f.3 version: 02 width: 32 bits clock: 33MHz configuration: latency=0 resources: ioport:f000(size=32) *-scsi:0 physical id: 2 bus info: usb@1:1 logical name: scsi4 capabilities: emulated scsi-host configuration: driver=usb-storage *-disk description: SCSI Disk physical id: 0.0.0 bus info: scsi@4:0.0.0 logical name: /dev/sdb size: 29GiB (31GB) capabilities: partitioned partitioned:dos configuration: signature=00017463 *-volume description: Windows FAT volume vendor: mkdosfs physical id: 1 bus info: scsi@4:0.0.0,1 logical name: /dev/sdb1 logical name: /cdrom version: FAT32 serial: 129b-4f87 size: 29GiB capacity: 29GiB capabilities: primary bootable fat initialized configuration: FATs=2 filesystem=fat mount.fstype=vfat mount.options=rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro state=mounted *-scsi:1 physical id: 3 bus info: usb@1:3.1 logical name: scsi6 capabilities: emulated scsi-host configuration: driver=usb-storage *-disk description: SCSI Disk physical id: 0.0.0 bus info: scsi@6:0.0.0 logical name: /dev/sdc size: 7400MiB (7759MB) capabilities: partitioned partitioned:dos configuration: signature=c3072e18 *-volume description: Windows FAT volume vendor: mkdosfs physical id: 1 bus info: scsi@6:0.0.0,1 logical name: /dev/sdc1 logical name: /media/JOUM8G version: FAT32 serial: e676-9311 size: 7394MiB capacity: 7394MiB capabilities: primary bootable fat initialized configuration: FATs=2 filesystem=fat label=Android mount.fstype=vfat mount.options=rw,nosuid,nodev,relatime,uid=999,gid=999,fmask=0022,dmask=0077,codepage=cp437,iocharset=iso8859-1,shortname=mixed,showexec,utf8,flush,errors=remount-ro state=mounted ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ xinput list ? Virtual core pointer id=2 [master pointer (3)] ? ? Virtual core XTEST pointer id=4 [slave pointer (2)] ? ? Plus More Enterprise LTD. USB-compliant keyboard id=10 [slave pointer (2)] ? ? USB Optical Mouse id=11 [slave pointer (2)] ? Virtual core keyboard id=3 [master keyboard (2)] ? Virtual core XTEST keyboard id=5 [slave keyboard (3)] ? Power Button id=6 [slave keyboard (3)] ? Power Button id=7 [slave keyboard (3)] ? Sleep Button id=8 [slave keyboard (3)] ? Plus More Enterprise LTD. USB-compliant keyboard id=9 [slave keyboard (3)] ? USB 2.0 Webcam - Front id=12 [slave keyboard (3)] ? AT Translated Set 2 keyboard id=13 [slave keyboard (3)] ubuntu@ubuntu:~$

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  • convert a logical partition to a primary partition

    - by ant2009
    Hello, Fedora 14 xfce I have the following partition setup. I would like to know how can I convert the logical partition sda6 to a primary partition. Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x1707a8a5 Device Boot Start End Blocks Id System /dev/sda1 2048 1026047 512000 83 Linux /dev/sda2 1026048 205844479 102409216 83 Linux /dev/sda3 205844480 214228991 4192256 82 Linux swap / Solaris /dev/sda4 214228992 625141759 205456384 5 Extended /dev/sda5 214231040 573562879 179665920 83 Linux /dev/sda6 573564928 625141759 25788416 7 HPFS/NTFS Filesystem Size Used Avail Use% Mounted on /dev/sda2 97G 5.0G 91G 6% / tmpfs 494M 176K 494M 1% /dev/shm /dev/sda1 485M 68M 392M 15% /boot /dev/sda5 169G 26G 135G 16% /home # partition table of /dev/sda unit: sectors /dev/sda1 : start= 2048, size= 1024000, Id=83 /dev/sda2 : start= 1026048, size=204818432, Id=83 /dev/sda3 : start=205844480, size= 8384512, Id=82 /dev/sda4 : start=214228992, size=410912768, Id= 5 /dev/sda5 : start=214231040, size=359331840, Id=83 /dev/sda6 : start=573564928, size= 51576832, Id= 7 I would like to convert sda6 to a primary partition, the reason for this it to install windows 7 starter. Many thanks for any suggestions,

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  • Creating a Logical network diagram

    - by user273284
    Im a student and I have been assigned the task of creating a logical network diagram for the following scenario There are 2 buildings, the first is the head office and the second is the branch. The data centre is in the head office, it contains domain controller, mail server, file server and a web server. it provides wired and wireless access to the staff. the branch building is new and it does not have a network. The two buildings must be connected using a VPN connection. The branch building will not have any servers but just network devices that will provide the connectivity, the users in the branch building will be connected to the head office over the VPN. I had created a diagram based on this scenario, but my teacher rejected it saying that it does not follow Cisco hierarchical Model and the servers were not placed correctly in the diagram. I just wanted some help in this matter so that I Can create my network diagram correctly. If anyone could upload a picture of how the logical diagram should be for this scenario will be helpful, any other resources would also be great.

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  • Advanced TSQL Tuning: Why Internals Knowledge Matters

    - by Paul White
    There is much more to query tuning than reducing logical reads and adding covering nonclustered indexes.  Query tuning is not complete as soon as the query returns results quickly in the development or test environments.  In production, your query will compete for memory, CPU, locks, I/O and other resources on the server.  Today’s entry looks at some tuning considerations that are often overlooked, and shows how deep internals knowledge can help you write better TSQL. As always, we’ll need some example data.  In fact, we are going to use three tables today, each of which is structured like this: Each table has 50,000 rows made up of an INTEGER id column and a padding column containing 3,999 characters in every row.  The only difference between the three tables is in the type of the padding column: the first table uses CHAR(3999), the second uses VARCHAR(MAX), and the third uses the deprecated TEXT type.  A script to create a database with the three tables and load the sample data follows: USE master; GO IF DB_ID('SortTest') IS NOT NULL DROP DATABASE SortTest; GO CREATE DATABASE SortTest COLLATE LATIN1_GENERAL_BIN; GO ALTER DATABASE SortTest MODIFY FILE ( NAME = 'SortTest', SIZE = 3GB, MAXSIZE = 3GB ); GO ALTER DATABASE SortTest MODIFY FILE ( NAME = 'SortTest_log', SIZE = 256MB, MAXSIZE = 1GB, FILEGROWTH = 128MB ); GO ALTER DATABASE SortTest SET ALLOW_SNAPSHOT_ISOLATION OFF ; ALTER DATABASE SortTest SET AUTO_CLOSE OFF ; ALTER DATABASE SortTest SET AUTO_CREATE_STATISTICS ON ; ALTER DATABASE SortTest SET AUTO_SHRINK OFF ; ALTER DATABASE SortTest SET AUTO_UPDATE_STATISTICS ON ; ALTER DATABASE SortTest SET AUTO_UPDATE_STATISTICS_ASYNC ON ; ALTER DATABASE SortTest SET PARAMETERIZATION SIMPLE ; ALTER DATABASE SortTest SET READ_COMMITTED_SNAPSHOT OFF ; ALTER DATABASE SortTest SET MULTI_USER ; ALTER DATABASE SortTest SET RECOVERY SIMPLE ; USE SortTest; GO CREATE TABLE dbo.TestCHAR ( id INTEGER IDENTITY (1,1) NOT NULL, padding CHAR(3999) NOT NULL,   CONSTRAINT [PK dbo.TestCHAR (id)] PRIMARY KEY CLUSTERED (id), ) ; CREATE TABLE dbo.TestMAX ( id INTEGER IDENTITY (1,1) NOT NULL, padding VARCHAR(MAX) NOT NULL,   CONSTRAINT [PK dbo.TestMAX (id)] PRIMARY KEY CLUSTERED (id), ) ; CREATE TABLE dbo.TestTEXT ( id INTEGER IDENTITY (1,1) NOT NULL, padding TEXT NOT NULL,   CONSTRAINT [PK dbo.TestTEXT (id)] PRIMARY KEY CLUSTERED (id), ) ; -- ============= -- Load TestCHAR (about 3s) -- ============= INSERT INTO dbo.TestCHAR WITH (TABLOCKX) ( padding ) SELECT padding = REPLICATE(CHAR(65 + (Data.n % 26)), 3999) FROM ( SELECT TOP (50000) n = ROW_NUMBER() OVER (ORDER BY (SELECT 0)) - 1 FROM master.sys.columns C1, master.sys.columns C2, master.sys.columns C3 ORDER BY n ASC ) AS Data ORDER BY Data.n ASC ; -- ============ -- Load TestMAX (about 3s) -- ============ INSERT INTO dbo.TestMAX WITH (TABLOCKX) ( padding ) SELECT CONVERT(VARCHAR(MAX), padding) FROM dbo.TestCHAR ORDER BY id ; -- ============= -- Load TestTEXT (about 5s) -- ============= INSERT INTO dbo.TestTEXT WITH (TABLOCKX) ( padding ) SELECT CONVERT(TEXT, padding) FROM dbo.TestCHAR ORDER BY id ; -- ========== -- Space used -- ========== -- EXECUTE sys.sp_spaceused @objname = 'dbo.TestCHAR'; EXECUTE sys.sp_spaceused @objname = 'dbo.TestMAX'; EXECUTE sys.sp_spaceused @objname = 'dbo.TestTEXT'; ; CHECKPOINT ; That takes around 15 seconds to run, and shows the space allocated to each table in its output: To illustrate the points I want to make today, the example task we are going to set ourselves is to return a random set of 150 rows from each table.  The basic shape of the test query is the same for each of the three test tables: SELECT TOP (150) T.id, T.padding FROM dbo.Test AS T ORDER BY NEWID() OPTION (MAXDOP 1) ; Test 1 – CHAR(3999) Running the template query shown above using the TestCHAR table as the target, we find that the query takes around 5 seconds to return its results.  This seems slow, considering that the table only has 50,000 rows.  Working on the assumption that generating a GUID for each row is a CPU-intensive operation, we might try enabling parallelism to see if that speeds up the response time.  Running the query again (but without the MAXDOP 1 hint) on a machine with eight logical processors, the query now takes 10 seconds to execute – twice as long as when run serially. Rather than attempting further guesses at the cause of the slowness, let’s go back to serial execution and add some monitoring.  The script below monitors STATISTICS IO output and the amount of tempdb used by the test query.  We will also run a Profiler trace to capture any warnings generated during query execution. DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TC.id, TC.padding FROM dbo.TestCHAR AS TC ORDER BY NEWID() OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; Let’s take a closer look at the statistics and query plan generated from this: Following the flow of the data from right to left, we see the expected 50,000 rows emerging from the Clustered Index Scan, with a total estimated size of around 191MB.  The Compute Scalar adds a column containing a random GUID (generated from the NEWID() function call) for each row.  With this extra column in place, the size of the data arriving at the Sort operator is estimated to be 192MB. Sort is a blocking operator – it has to examine all of the rows on its input before it can produce its first row of output (the last row received might sort first).  This characteristic means that Sort requires a memory grant – memory allocated for the query’s use by SQL Server just before execution starts.  In this case, the Sort is the only memory-consuming operator in the plan, so it has access to the full 243MB (248,696KB) of memory reserved by SQL Server for this query execution. Notice that the memory grant is significantly larger than the expected size of the data to be sorted.  SQL Server uses a number of techniques to speed up sorting, some of which sacrifice size for comparison speed.  Sorts typically require a very large number of comparisons, so this is usually a very effective optimization.  One of the drawbacks is that it is not possible to exactly predict the sort space needed, as it depends on the data itself.  SQL Server takes an educated guess based on data types, sizes, and the number of rows expected, but the algorithm is not perfect. In spite of the large memory grant, the Profiler trace shows a Sort Warning event (indicating that the sort ran out of memory), and the tempdb usage monitor shows that 195MB of tempdb space was used – all of that for system use.  The 195MB represents physical write activity on tempdb, because SQL Server strictly enforces memory grants – a query cannot ‘cheat’ and effectively gain extra memory by spilling to tempdb pages that reside in memory.  Anyway, the key point here is that it takes a while to write 195MB to disk, and this is the main reason that the query takes 5 seconds overall. If you are wondering why using parallelism made the problem worse, consider that eight threads of execution result in eight concurrent partial sorts, each receiving one eighth of the memory grant.  The eight sorts all spilled to tempdb, resulting in inefficiencies as the spilled sorts competed for disk resources.  More importantly, there are specific problems at the point where the eight partial results are combined, but I’ll cover that in a future post. CHAR(3999) Performance Summary: 5 seconds elapsed time 243MB memory grant 195MB tempdb usage 192MB estimated sort set 25,043 logical reads Sort Warning Test 2 – VARCHAR(MAX) We’ll now run exactly the same test (with the additional monitoring) on the table using a VARCHAR(MAX) padding column: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TM.id, TM.padding FROM dbo.TestMAX AS TM ORDER BY NEWID() OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; This time the query takes around 8 seconds to complete (3 seconds longer than Test 1).  Notice that the estimated row and data sizes are very slightly larger, and the overall memory grant has also increased very slightly to 245MB.  The most marked difference is in the amount of tempdb space used – this query wrote almost 391MB of sort run data to the physical tempdb file.  Don’t draw any general conclusions about VARCHAR(MAX) versus CHAR from this – I chose the length of the data specifically to expose this edge case.  In most cases, VARCHAR(MAX) performs very similarly to CHAR – I just wanted to make test 2 a bit more exciting. MAX Performance Summary: 8 seconds elapsed time 245MB memory grant 391MB tempdb usage 193MB estimated sort set 25,043 logical reads Sort warning Test 3 – TEXT The same test again, but using the deprecated TEXT data type for the padding column: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) TT.id, TT.padding FROM dbo.TestTEXT AS TT ORDER BY NEWID() OPTION (MAXDOP 1, RECOMPILE) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; This time the query runs in 500ms.  If you look at the metrics we have been checking so far, it’s not hard to understand why: TEXT Performance Summary: 0.5 seconds elapsed time 9MB memory grant 5MB tempdb usage 5MB estimated sort set 207 logical reads 596 LOB logical reads Sort warning SQL Server’s memory grant algorithm still underestimates the memory needed to perform the sorting operation, but the size of the data to sort is so much smaller (5MB versus 193MB previously) that the spilled sort doesn’t matter very much.  Why is the data size so much smaller?  The query still produces the correct results – including the large amount of data held in the padding column – so what magic is being performed here? TEXT versus MAX Storage The answer lies in how columns of the TEXT data type are stored.  By default, TEXT data is stored off-row in separate LOB pages – which explains why this is the first query we have seen that records LOB logical reads in its STATISTICS IO output.  You may recall from my last post that LOB data leaves an in-row pointer to the separate storage structure holding the LOB data. SQL Server can see that the full LOB value is not required by the query plan until results are returned, so instead of passing the full LOB value down the plan from the Clustered Index Scan, it passes the small in-row structure instead.  SQL Server estimates that each row coming from the scan will be 79 bytes long – 11 bytes for row overhead, 4 bytes for the integer id column, and 64 bytes for the LOB pointer (in fact the pointer is rather smaller – usually 16 bytes – but the details of that don’t really matter right now). OK, so this query is much more efficient because it is sorting a very much smaller data set – SQL Server delays retrieving the LOB data itself until after the Sort starts producing its 150 rows.  The question that normally arises at this point is: Why doesn’t SQL Server use the same trick when the padding column is defined as VARCHAR(MAX)? The answer is connected with the fact that if the actual size of the VARCHAR(MAX) data is 8000 bytes or less, it is usually stored in-row in exactly the same way as for a VARCHAR(8000) column – MAX data only moves off-row into LOB storage when it exceeds 8000 bytes.  The default behaviour of the TEXT type is to be stored off-row by default, unless the ‘text in row’ table option is set suitably and there is room on the page.  There is an analogous (but opposite) setting to control the storage of MAX data – the ‘large value types out of row’ table option.  By enabling this option for a table, MAX data will be stored off-row (in a LOB structure) instead of in-row.  SQL Server Books Online has good coverage of both options in the topic In Row Data. The MAXOOR Table The essential difference, then, is that MAX defaults to in-row storage, and TEXT defaults to off-row (LOB) storage.  You might be thinking that we could get the same benefits seen for the TEXT data type by storing the VARCHAR(MAX) values off row – so let’s look at that option now.  This script creates a fourth table, with the VARCHAR(MAX) data stored off-row in LOB pages: CREATE TABLE dbo.TestMAXOOR ( id INTEGER IDENTITY (1,1) NOT NULL, padding VARCHAR(MAX) NOT NULL,   CONSTRAINT [PK dbo.TestMAXOOR (id)] PRIMARY KEY CLUSTERED (id), ) ; EXECUTE sys.sp_tableoption @TableNamePattern = N'dbo.TestMAXOOR', @OptionName = 'large value types out of row', @OptionValue = 'true' ; SELECT large_value_types_out_of_row FROM sys.tables WHERE [schema_id] = SCHEMA_ID(N'dbo') AND name = N'TestMAXOOR' ; INSERT INTO dbo.TestMAXOOR WITH (TABLOCKX) ( padding ) SELECT SPACE(0) FROM dbo.TestCHAR ORDER BY id ; UPDATE TM WITH (TABLOCK) SET padding.WRITE (TC.padding, NULL, NULL) FROM dbo.TestMAXOOR AS TM JOIN dbo.TestCHAR AS TC ON TC.id = TM.id ; EXECUTE sys.sp_spaceused @objname = 'dbo.TestMAXOOR' ; CHECKPOINT ; Test 4 – MAXOOR We can now re-run our test on the MAXOOR (MAX out of row) table: DECLARE @read BIGINT, @write BIGINT ; SELECT @read = SUM(num_of_bytes_read), @write = SUM(num_of_bytes_written) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; SET STATISTICS IO ON ; SELECT TOP (150) MO.id, MO.padding FROM dbo.TestMAXOOR AS MO ORDER BY NEWID() OPTION (MAXDOP 1, RECOMPILE) ; SET STATISTICS IO OFF ; SELECT tempdb_read_MB = (SUM(num_of_bytes_read) - @read) / 1024. / 1024., tempdb_write_MB = (SUM(num_of_bytes_written) - @write) / 1024. / 1024., internal_use_MB = ( SELECT internal_objects_alloc_page_count / 128.0 FROM sys.dm_db_task_space_usage WHERE session_id = @@SPID ) FROM tempdb.sys.database_files AS DBF JOIN sys.dm_io_virtual_file_stats(2, NULL) AS FS ON FS.file_id = DBF.file_id WHERE DBF.type_desc = 'ROWS' ; TEXT Performance Summary: 0.3 seconds elapsed time 245MB memory grant 0MB tempdb usage 193MB estimated sort set 207 logical reads 446 LOB logical reads No sort warning The query runs very quickly – slightly faster than Test 3, and without spilling the sort to tempdb (there is no sort warning in the trace, and the monitoring query shows zero tempdb usage by this query).  SQL Server is passing the in-row pointer structure down the plan and only looking up the LOB value on the output side of the sort. The Hidden Problem There is still a huge problem with this query though – it requires a 245MB memory grant.  No wonder the sort doesn’t spill to tempdb now – 245MB is about 20 times more memory than this query actually requires to sort 50,000 records containing LOB data pointers.  Notice that the estimated row and data sizes in the plan are the same as in test 2 (where the MAX data was stored in-row). The optimizer assumes that MAX data is stored in-row, regardless of the sp_tableoption setting ‘large value types out of row’.  Why?  Because this option is dynamic – changing it does not immediately force all MAX data in the table in-row or off-row, only when data is added or actually changed.  SQL Server does not keep statistics to show how much MAX or TEXT data is currently in-row, and how much is stored in LOB pages.  This is an annoying limitation, and one which I hope will be addressed in a future version of the product. So why should we worry about this?  Excessive memory grants reduce concurrency and may result in queries waiting on the RESOURCE_SEMAPHORE wait type while they wait for memory they do not need.  245MB is an awful lot of memory, especially on 32-bit versions where memory grants cannot use AWE-mapped memory.  Even on a 64-bit server with plenty of memory, do you really want a single query to consume 0.25GB of memory unnecessarily?  That’s 32,000 8KB pages that might be put to much better use. The Solution The answer is not to use the TEXT data type for the padding column.  That solution happens to have better performance characteristics for this specific query, but it still results in a spilled sort, and it is hard to recommend the use of a data type which is scheduled for removal.  I hope it is clear to you that the fundamental problem here is that SQL Server sorts the whole set arriving at a Sort operator.  Clearly, it is not efficient to sort the whole table in memory just to return 150 rows in a random order. The TEXT example was more efficient because it dramatically reduced the size of the set that needed to be sorted.  We can do the same thing by selecting 150 unique keys from the table at random (sorting by NEWID() for example) and only then retrieving the large padding column values for just the 150 rows we need.  The following script implements that idea for all four tables: SET STATISTICS IO ON ; WITH TestTable AS ( SELECT * FROM dbo.TestCHAR ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id = ANY (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestMAX ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestTEXT ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; WITH TestTable AS ( SELECT * FROM dbo.TestMAXOOR ), TopKeys AS ( SELECT TOP (150) id FROM TestTable ORDER BY NEWID() ) SELECT T1.id, T1.padding FROM TestTable AS T1 WHERE T1.id IN (SELECT id FROM TopKeys) OPTION (MAXDOP 1) ; SET STATISTICS IO OFF ; All four queries now return results in much less than a second, with memory grants between 6 and 12MB, and without spilling to tempdb.  The small remaining inefficiency is in reading the id column values from the clustered primary key index.  As a clustered index, it contains all the in-row data at its leaf.  The CHAR and VARCHAR(MAX) tables store the padding column in-row, so id values are separated by a 3999-character column, plus row overhead.  The TEXT and MAXOOR tables store the padding values off-row, so id values in the clustered index leaf are separated by the much-smaller off-row pointer structure.  This difference is reflected in the number of logical page reads performed by the four queries: Table 'TestCHAR' logical reads 25511 lob logical reads 000 Table 'TestMAX'. logical reads 25511 lob logical reads 000 Table 'TestTEXT' logical reads 00412 lob logical reads 597 Table 'TestMAXOOR' logical reads 00413 lob logical reads 446 We can increase the density of the id values by creating a separate nonclustered index on the id column only.  This is the same key as the clustered index, of course, but the nonclustered index will not include the rest of the in-row column data. CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestCHAR (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestMAX (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestTEXT (id); CREATE UNIQUE NONCLUSTERED INDEX uq1 ON dbo.TestMAXOOR (id); The four queries can now use the very dense nonclustered index to quickly scan the id values, sort them by NEWID(), select the 150 ids we want, and then look up the padding data.  The logical reads with the new indexes in place are: Table 'TestCHAR' logical reads 835 lob logical reads 0 Table 'TestMAX' logical reads 835 lob logical reads 0 Table 'TestTEXT' logical reads 686 lob logical reads 597 Table 'TestMAXOOR' logical reads 686 lob logical reads 448 With the new index, all four queries use the same query plan (click to enlarge): Performance Summary: 0.3 seconds elapsed time 6MB memory grant 0MB tempdb usage 1MB sort set 835 logical reads (CHAR, MAX) 686 logical reads (TEXT, MAXOOR) 597 LOB logical reads (TEXT) 448 LOB logical reads (MAXOOR) No sort warning I’ll leave it as an exercise for the reader to work out why trying to eliminate the Key Lookup by adding the padding column to the new nonclustered indexes would be a daft idea Conclusion This post is not about tuning queries that access columns containing big strings.  It isn’t about the internal differences between TEXT and MAX data types either.  It isn’t even about the cool use of UPDATE .WRITE used in the MAXOOR table load.  No, this post is about something else: Many developers might not have tuned our starting example query at all – 5 seconds isn’t that bad, and the original query plan looks reasonable at first glance.  Perhaps the NEWID() function would have been blamed for ‘just being slow’ – who knows.  5 seconds isn’t awful – unless your users expect sub-second responses – but using 250MB of memory and writing 200MB to tempdb certainly is!  If ten sessions ran that query at the same time in production that’s 2.5GB of memory usage and 2GB hitting tempdb.  Of course, not all queries can be rewritten to avoid large memory grants and sort spills using the key-lookup technique in this post, but that’s not the point either. The point of this post is that a basic understanding of execution plans is not enough.  Tuning for logical reads and adding covering indexes is not enough.  If you want to produce high-quality, scalable TSQL that won’t get you paged as soon as it hits production, you need a deep understanding of execution plans, and as much accurate, deep knowledge about SQL Server as you can lay your hands on.  The advanced database developer has a wide range of tools to use in writing queries that perform well in a range of circumstances. By the way, the examples in this post were written for SQL Server 2008.  They will run on 2005 and demonstrate the same principles, but you won’t get the same figures I did because 2005 had a rather nasty bug in the Top N Sort operator.  Fair warning: if you do decide to run the scripts on a 2005 instance (particularly the parallel query) do it before you head out for lunch… This post is dedicated to the people of Christchurch, New Zealand. © 2011 Paul White email: @[email protected] twitter: @SQL_Kiwi

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  • Data Modeling Resources

    - by Dejan Sarka
    You can find many different data modeling resources. It is impossible to list all of them. I selected only the most valuable ones for me, and, of course, the ones I contributed to. Books Chris J. Date: An Introduction to Database Systems – IMO a “must” to understand the relational model correctly. Terry Halpin, Tony Morgan: Information Modeling and Relational Databases – meet the object-role modeling leaders. Chris J. Date, Nikos Lorentzos and Hugh Darwen: Time and Relational Theory, Second Edition: Temporal Databases in the Relational Model and SQL – all theory needed to manage temporal data. Louis Davidson, Jessica M. Moss: Pro SQL Server 2012 Relational Database Design and Implementation – the best SQL Server focused data modeling book I know by two of my friends. Dejan Sarka, et al.: MCITP Self-Paced Training Kit (Exam 70-441): Designing Database Solutions by Using Microsoft® SQL Server™ 2005 – SQL Server 2005 data modeling training kit. Most of the text is still valid for SQL Server 2008, 2008 R2, 2012 and 2014. Itzik Ben-Gan, Lubor Kollar, Dejan Sarka, Steve Kass: Inside Microsoft SQL Server 2008 T-SQL Querying – Steve wrote a chapter with mathematical background, and I added a chapter with theoretical introduction to the relational model. Itzik Ben-Gan, Dejan Sarka, Roger Wolter, Greg Low, Ed Katibah, Isaac Kunen: Inside Microsoft SQL Server 2008 T-SQL Programming – I added three chapters with theoretical introduction and practical solutions for the user-defined data types, dynamic schema and temporal data. Dejan Sarka, Matija Lah, Grega Jerkic: Training Kit (Exam 70-463): Implementing a Data Warehouse with Microsoft SQL Server 2012 – my first two chapters are about data warehouse design and implementation. Courses Data Modeling Essentials – I wrote a 3-day course for SolidQ. If you are interested in this course, which I could also deliver in a shorter seminar way, you can contact your closes SolidQ subsidiary, or, of course, me directly on addresses [email protected] or [email protected]. This course could also complement the existing courseware portfolio of training providers, which are welcome to contact me as well. Logical and Physical Modeling for Analytical Applications – online course I wrote for Pluralsight. Working with Temporal data in SQL Server – my latest Pluralsight course, where besides theory and implementation I introduce many original ways how to optimize temporal queries. Forthcoming presentations SQL Bits 12, July 17th – 19th, Telford, UK – I have a full-day pre-conference seminar Advanced Data Modeling Topics there.

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  • Different block sizes for partition and underlying logical disk on HP Raid Controller (Linux)

    - by Wawrzek
    Following links collected in this thread I started to check blockdev and found the following output indicating different sizes for partition c0d9p1 and the underlying device (c0d9): [root@machine ~]# blockdev --report /dev/cciss/c0d9 RO RA SSZ BSZ StartSec Size Device rw 256 512 4096 0 3906963632 /dev/cciss/c0d9 [root@machine ~]# blockdev --report /dev/cciss/c0d9p1 RO RA SSZ BSZ StartSec Size Device rw 256 512 2048 1 3906959039 /dev/cciss/c0d9p1 We have a lot of small files, so yes the block size is smaller than normal. The device is a logical driver on an HP P410 raid controller, simple disk without any raid - RAID 0 on one disk to be precise. (Please note that above configuration is a feature not a bug). Therefore, I have the following questions. Can the above discrepancy in the block size affect disk performance? Can I control the block size using hpacucli?

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  • Impossible remove Logical Volumes or Volume Group LVM2

    - by abkrim
    After a disk crash part of a LVM group, I can't use LVM2 properly. If like delete a Logical Volume impossible (Error on SATA Volumen) lvscan Couldn't find device with uuid vxHO8W-FPbL-9d5N-GUVb-Lo8d-D9WZ-1RY3Bx. inactive '/dev/sata/isos' [100.00 GiB] inherit inactive '/dev/sata/vm-999-disk-1' [10.00 GiB] inherit inactive '/dev/sata/vm-300-disk-1' [51.00 GiB] inherit ACTIVE '/dev/pve/vm-103-disk-1' [200.00 GiB] inherit lvremove /dev/sata/isos Couldn't find device with uuid vxHO8W-FPbL-9d5N-GUVb-Lo8d-D9WZ-1RY3Bx. Segmentation fault dmsetup remove --force sata device-mapper: table ioctl on sata failed: No such device or address device-mapper: reload ioctl on sata failed: No such device or address device-mapper: remove ioctl on sata failed: No such device or address Command failed Try also, vgreduce --removemissing, and other commands for delete ALL on SATA Volumen and start form 0. PVE volumen it's on production. Apreciate help

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  • Uninstall grub from logical partition

    - by Andrew Fleenor
    I'm multi-booting with Windows 7 x64 and (at least) Linux Mint. Because I hadn't yet made a backup of my MBR, when I installed Linux mint on a logical partition, I told the installer to put GRUB on the partition instead of in the MBR. This turned out to be useless, as I need to use GRUB from a boot disk to get into the GRUB I installed... Before installing it in the MBR, I'd like to get it out of the partition, preferably without wiping and reinstalling Linux. I don't relish the prospect of going through two layers of GRUB when I want to boot Linux. How do I get it out, or what other options are available to me?

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  • Logical operator AND having higher order of precedence than IN

    - by AspOnMyNet
    I’ve read that logical operator AND has higher order of precedence than logical operator IN, but that doesn’t make sense since if that was true, then wouldn’t in the following statement the AND condition got evaluated before the IN condition ( thus before IN operator would be able to check whether Released field equals to any of the values specified within parentheses ? SELECT Song, Released, Rating FROM Songs WHERE Released IN (1967, 1977, 1987) AND SongName = ’WTTJ’ thanx

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  • Logical equality in C

    - by andrew cooke
    [It seems odd this doesn't exist, so apologies in advance if it's a duplicate] I want to test for logical equality in C. In other words, I want to know whether two values would be equal if both were converted in the normal way associated with logical expressions. In C99, I think that (bool)a == (bool)b gives what I want. Is that correct? What is the normal way of writing this in traditional C?

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  • Fix bad superblock on logical partition

    - by Chris
    I was following http://www.howtoforge.com/linux_resi...xt3_partitions and when i reboot and run: root@Microknoppix:/home/knoppix# fsck -n /dev/sda7 fsck from util-linux-ng 2.17.2 e2fsck 1.41.12 (17-May-2010) fsck.ext2: Superblock invalid, trying backup blocks... fsck.ext2: Bad magic number in super-block while trying to open /dev/sda7 The superblock could not be read or does not describe a correct ext2 filesystem. If the device is valid and it really contains an ext2 filesystem (and not swap or ufs or something else), then the superblock is corrupt, and you might try running e2fsck with an alternate superblock: e2fsck -b 8193 <device> so i ran e2fsck with all the block numbers that you need (forget exactly what tool i used to find where the superblocks are hidden) no dice then i ran testdisk and had it look for the superblock, no results anyone have any ideas? fdisk -l for reference: root@Microknoppix:/home/knoppix# fdisk -l Disk /dev/sda: 320.1 GB, 320072933376 bytes 255 heads, 63 sectors/track, 38913 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x97646c29 Device Boot Start End Blocks Id System /dev/sda1 1 64 512000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 64 38912 312046593 f W95 Ext'd (LBA) /dev/sda5 64 326 2104320 82 Linux swap / Solaris /dev/sda6 * 327 2938 20972544 83 Linux /dev/sda7 2938 38912 288968672+ 83 Linux To be honest it looks like I lost it... Next step if that happens is to dump the partition to an image file and hope i can find or write some software to parse through the data looking for known file headers, i think.

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