A quick tip for optimizing TCP performance on linux.
edit /etc/sysctl.conf add the lines:
If using gigabit ethernet:
net.ipv4.tcp_mem= 98304 131072 196608
net.ipv4.tcp_window_scaling=1
net.core.wmem_default = 65536
net.core.rmem_default = 65536
net.core.wmem_max=8388608
To reload these use:
# sysctl -p
If using infiniband:
net.ipv4.tcp_window_scaling=1
net.ipv4.tcp_timestamps=0
net.ipv4.tcp_sack=0
net.ipv4.tcp_rmem=10000000 10000000 10000000
net.ipv4.tcp_wmem=10000000 10000000 10000000
net.ipv4.tcp_mem=10000000 10000000 10000000
net.core.rmem_max=524287
net.core.wmem_max=524287
net.core.rmem_default=524287
net.core.wmem_default=524287
net.core.optmem_max=524287
net.core.netdev_max_backlog=300000
COPY DATABASE <name> TO <name> [ IF [ NOT ] EXISTS ]This command is used to copy an existing database to a new database. By default an error will be returned if the target database already exists. Specifying the optional IF NOT EXISTS keywords no error will be returned if the target database already exists. If the optional IF EXISTS keywords are specified and the target database already exists, then it will be removed before the copy. Both the databases must be closed before they can be copied.
It would appear that gigabit LAN is not! In fact it often runs at the same speed as 100Mbps LAN. Let's look at why exactly.
After configuring your network you can use the ifconfig command to see what speeds the LAN is connected. Even though 1000Mbps is reported by the card, the reality is that the overall throughtput may well be ~100Mpbs. You can try copying a large file using scp to demonstrate this.
As it turns out, in order to use a gigabit LAN you need to use CAT6 cables. CAT5 and CAT5E are not good enough. End result, the ethernet cards throttle back the speed to reduce dropped packets and errors.
You can find a good article here titled Squeeze Your Gigabit NIC for Top Performance. After tuning up the TCP parameters i found that it made no dfifference. The principal reasons behind low gigabit ethernet performance can be summed up as follows.
- Need to use CAT6 cables
- Slow Disk speed
- Limitations of the PCI bus which the gigabit ethernet cards use
You can get an idea about the disk speed using the hdparm command:
Display the disk partitions and choose the main linux partition which has the / filesystem.
# fdisk -l
Then get disk cache and disk read statistics:
# hdparm -Tt /dev/sda0
On my desktop system the sata disk perfomance is a limiting factor. These were the results:
/dev/sda1:
Timing cached reads: 9984 MB in 2.00 seconds = 4996.41 MB/sec
Timing buffered disk reads: 84 MB in 3.13 seconds = 58.49 MB/sec
Well, that equates to a raw disk read speed of 58.49 * 8 = 467Mbps which is half the speed of a gigabit LAN.
So.. NAS storage with lots of memory looks to be the way to go... If you use the right cables!
Another useful article on IBM developerworks shows how to build PHP extensions using SWIG. You can find the article here.
If you have a live linux site that is running vmware virtual machines, you can pause the virtual machines when you want to perform a backup, I use acronis for linux which does incremental backups and you can specify a command to run before and after the backup, this allows backups to be performed at scheduled times daily without any intervention. In my examples below, the virtual machine i want to control is in /root/vmware/Recital/Recital.vmx
To pause the virtual machine on linux:
# vmrun pause /root/vmware/Recital/Recital.vmx
and then to unpause after the backup has completed:
# vmrun unpause /root/vmware/Recital/Recital.vmx
That is basicallty it, no need to attend the backup and it can be perfomed at a suitable time so no users are affected.
Incidentally, vmrun lets you startup a virtual machine at system startup too, without needing the GUI:
# vmrun start /root/vmware/Recital/Recital.vmx
Or alternatively stop it:
# vmrun stop /root/vmware/Recital/Recital.vmx
There are lots of other capabilities of this command, running applications inside the virtual machine etc etc. For full details just type vmrun in a terminal window.
# recital < mrprog.prgIndividual commands can be executed in shell scripts.
# recital < myprog.prg > myoutput.txt
# recital > myoutput.txt <<END
use customers
list structure
END
# echo "select * from sales!customers where overdue" | recital | wc -l
# recital -c "create database sales"Expressions can be evaluated and used in shell scripts.
# recital -c "create table sales!invoices (id int, name char(25), due date)"
# VER=`recital -e "version(1)"`You can view what command line options are available by typing:
# recital --help
When installing nomachine on redhat 5.3 64-bit be sure to:
- Make sure you have installed the 64-bit packages as the 32-bit ones will not work.
- add the hostname to /etc/hosts
- Check "Disable encryption of all traffic" (in configuration / advanced tab)
- add the hostname to /etc/hosts
- make sure the host IP is not specified as 127.0.0.1 line
- Uncheck "Disable encryption of all traffic" (in configuration / advanced tab)
try
open database southwind
catch
die("Cannot open database, please try later.")
endtry
Key features of the Recital scripting language include:
What are the key feature of the Recital database?
- High performance database application scripting language
- Modern object-oriented language features
- Easy to learn, easy to use
- Fast, just-in-time compiled
- Develop desktop or web applications
- Cross-platform support
- Extensive built-in functions
- Superb built-in SQL command integration
- Navigational data access for the most demanding applications