Ext3 commits writes to disk within approximately 5 seconds - Ext4 can take from 40-150 seconds. In addition, if a system is using Ext3 and crashes before the commit takes place you will still have the previous contents of a file where under Ext4 the file will be empty. Theodore Tso feels that this is a failure at the application level and that the file system is behaving as designed and as specified by the POSIX spec (which apparently does not specify what is supposed to happen when a system is not shut down cleanly). His solution to the issue is to suggest proper use of fsync() and lists various scenarios/examples in post 54 of the bug report (linked above). In addition he wrote a patch that recognize the rename() situation mentioned in his post 54 yet retains the normal Ext4 behaviors and performance in the majority of cases. Also a more "proper" solution has been provided which allows the behavior of Ext3 to be retained under Ext4 by mounting it with alloc_on_commit.
A somewhat related topic is the use of on-board caching by hard drives. This behavior can be modified on most drives by using hdparm.
In this article Barry Mavin, CEO and Chief Software Architect for Recital, details how to use the Recital Database Server with Visual FoxPro.
APPEND FROM TYPE CSV <file-name.csv>The TYPE keyword has now been enhanced to support a comma separated values (CSV) format
Recital is a rich and versatile product with many ways to do the same thing. Developers usually write code in the way that they are accustomed to without paying much attention to how this will perform in a multi-user environment with large amounts of users and transactions. The best way to optimize Recital applications is to use the built-in tuning capabilities introduced in Recital 10.
sernet.de maintain the latest Samba releases in a yum repository, allowing for an easy and painless install or upgrade of Samba on your yum based Linux distribution.
To install the latest available Samba execute the following commands at the shell:
# cd /etc/yum.repos.d # wget http://ftp.sernet.de/pub/samba/experimental/centos/5/sernet-samba.repo # yum install samba
To upgrade an existing Samba install:
# cd /etc/yum.repos.d # wget http://ftp.sernet.de/pub/samba/experimental/centos/5/sernet-samba.repo ## Note: edit sernet-samba.repo and add the line "gpgcheck=false" otherwise ## it will not install as it is not signed
# yum update samba
Note: These steps will install the very latest build available at sernet.de.
If you require a less bleeding edge version of Samba, use the "tested" repo. This can be found at the following URL: http://ftp.sernet.de/pub/samba/tested/rhel/5
After split brain has been detected, one node will always have the resource in a StandAlone connection state. The other might either also be in the StandAlone state (if both nodes detected the split brain simultaneously), or in WFConnection (if the peer tore down the connection before the other node had a chance to detect split brain).
At this point, unless you configured DRBD to automatically recover from split brain, you must manually intervene by selecting one node whose modifications will be discarded (this node is referred to as the split brain victim). This intervention is made with the following commands:
# drbdadm secondary resource
# drbdadm disconnect resource
# drbdadm -- --discard-my-data connect resource
On the other node (the split brain survivor), if its connection state is also StandAlone, you would enter:
# drbdadm connect resource
You may omit this step if the node is already in the WFConnection state; it will then reconnect automatically.
If all else fails and the machines are still in a split-brain condition then on the secondary (backup) machine issue:
drbdadm invalidate resource
If you have 4 GB or more RAM use the Linux kernel compiled for PAE capable machines. Your machine may not show up total 4GB ram. All you have to do is install PAE kernel package.
This package includes a version of the Linux kernel with support for up to 64GB of high memory. It requires a CPU with Physical Address Extensions (PAE).
The non-PAE kernel can only address up to 4GB of memory. Install the kernel-PAE package if your machine has more than 4GB of memory (>=4GB).
# yum install kernel-PAE
If you want to know how much memory centos is using type this in a terminal:
# cat /proc/meminfo
Recital provides the following additional benefits:
- Easy to Install and Deploy - Users can set up Recital in minutes enabling organizations to deliver new applications faster than other databases.
- Easy to Administer - Recital is a low administration database that eliminates the need for highly trained, skilled, and costly database administrators to maintain the database.
- High Performance - Superior database performance for the most demanding of OLTP applications. Additionally, Clustered Recital provides 99.999% availability.
- Embeddable Library - Recital Embedded Edition provides in-process data storage engine that delivers all the features of a traditional relational database but in a size which makes it ideally suited for ISVs/VARs who need a small footprint and easy to use toolkit.
- Platform Independence - Recital runs on Linux, Solaris, AIX, HP-UX, Windows, and Mac OS X giving organizations complete flexibility in delivering a solution on the platform of their choice.
// declare some simple procedures
proc display(cArg)
echo "display=" + cArg
endproc
proc show(cArg)
echo "show=" + cArg
endproc
// create an object based on an anonymous class
myobj = new object()
// add some properties
myobj["name"] = "barry"
myobj["company"] = "recital"
// now declare an anonymous method
myobj["mymethod"] = display
// call the method
myobj.mymethod("hello world") // displays "display=hello world"
// redeclare the method
myobj["mymethod"] = show
// call the method
myobj.mymethod("hello world") // displays "show=hello world"
Where this becomes particularly useful is when you have a procedure that calls anonymous methods in order to process data. This technique can be used to call anonymous procedures in your code.
proc processdata(oArg)
oArg.mymethod(oArg.name)
endproc
proc show(cArg)
echo "show=" + cArg
endproc
myobj = new object()
myobj["name"] = "barry"
myobj["mymethod"] = show
processdata(myobj) // displays "show=barry"