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This website runs in a  virtual machine under vmware server. It is clustered between two servers using heartbeat and DRBD.
 
When VMware server starts up a virtual machine it generates a uuid (unique id) based on the machine it is running on and stores this in the .vmx file.
 
When heartbeat switches from slave to master, it will start VMware server (which is setup as a resource in the haresources file).
 
Virtual machines that you want started automatically when you start VMware server will not start because the uuid changes between the master and backup systems. To get around this problem always do the following:
  • edit the .vmx file and add the following line

    uuid.action = "keep"
If this is not done then everytime you try to run the virtual machine on the backup system in your cluster, VMware server will complain that the virtual machine has been copied or moved and it will not start it.
  • set the virtual machine to power off when vmware is stopped. Do not set this to "suspend" or it will not restart on the backup machine.
This will allow the virtual machine to start properly on the backup machine.
 
 
 
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Recital 10 introduced the ECHO command. This command operates in the same way as the PHP ECHO command. It does not append a newline to the output but rather operates in the same way as the existing ?? command in Recital. The string being output can contain C-style string escapes \n \t or \r (newline, tab and carriage return respectively) e.g.
echo "Hello world\n"
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SE Linux is a feature of the Linux kernel that provides mandatory access control. This policy based access control system grants far greater control over the resources on a machine than standard Linux access controls such as permissions.

Many modern Linux distributions are shipping with SELinux enabled by default, Fedora 14 and Rhel 6 both install with it enabled.

When you run Recital Web on a SELinux enabled machine and navigate to the default.rsp page you will see something similar to the screen shot below.

1
If you launch the SELinux troubleshooter you will see the following problem.

SELinux is blocking the apache server from accessing the Recital server running on port 8001.

2
To manage you SELinux policy you must have the policycoreutils package group installed. The policycoreutils contains the policy core utilities that are required for basic operation of a SELinux system.

If you wish to use a GUI tool, you must install the policycoreutils-gui package.

At the command prompt execute the following:

As root

$ yum install policycoreutils

$ semanage port -a -t http_port_t -p tcp 8001

$ service recital restart

$ service httpd restart 
 

We use the semanage command here to allow the http server access to port 8001. Once you have completed the steps detailed above you can go and navigate back to the default.rsp page in your borwser, where you will find the permission denied message is now replaced by the default.rsp page.


4
SELinux does a great job of restricting services and daemons so rather than simply disabling it, why not work with it!

When it comes to security, every little bit helps...

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Recital is a dynamic programming language with an integrated high performance database particularly well suited for the development and deployment of high transaction throughput applications.  Recital 10 further enhances Recital with extensive features and functionality to facilitate its use in fault tolerant high availability systems. Much of the development of Recital 10 was concentrated on performance optimizations and cluster aware functionality to provide an application platform that can be scaled as needed without any application changes. 

Key features of Recital 10 include:

  • Cluster aware database engine that works transparently with drbd, heartbeat, glusterfs and samba
  • High degree of fault tolerance with self healing indexes
  • Massive performance improvements 
  • Extensive internals overall and modernization with superior object-oriented capabilities
  • Chronological data versioning with database timelines
  • SmartQuery caching
  • Database Administration Tools
  • Code and Data Profiling
  • Better integration with unix/linux command shell
  • Incorporates a range of new built-in functions compatible with those in the PHP core libraries
  • Built-in support for outputting data in HTML, XML, and JSON format
  • Seamless SQL command integration into the Recital scripting language
  • Much improved Microsoft FoxPRO language compatibility
  • Numerous extensions and improvements (see below for details)
  • Very large file support (2^63)
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DRBD:
DRBD (Distributed Replicated Block Device) forms the storage redundancy portition of a HA cluster setup. Explained in basic terms DRBD provides a means of achieving RAID 1 behavoir over a network, where whole block devices are mirrored accross the network.

To start off you will need 2 indentically sized raw drives or partitions. Many how-to's on the internet assume the use of whole drives, of course this will be better performance, but if you are simply getting familar with the technology you can repartition existing drives to allow for two eqaully sized raw partitions, one on each of the systems you will be using.

There are 3 DRBD replication modes:
• Protocol A: Write I/O is reported as completed as soon as it reached local disk and local TCP send buffer
• Protocol B: Write I/O is reported as completed as soon as it reached local disk and remote TCP buffer cache
• Protocol C: Write I/O is reported as completed as soon as it reached both local and remote disks.

If we were installing the HA cluster on a slow LAN or if the geogrphical seperation of the systems involved was great, then I recommend you opt for asyncronous mirroring (Protocol A) where the notifcation of a completed write operation occurs as soon as the local disk write is performed. This will greatly improve performance.

As we are setting up our HA cluster connected via a fast LAN, we will be using DRBD in fully syncronous mode, protocol C.
Protocol C involves the file system on the active node only being notified that the write operation was finished when the block is written to both disks of the cluster. Protocol C is the most commonly used mode of DRBD.

/etc/drbd.conf

global { usage-count yes; }
common { syncer { rate 10M; } }
resource r0 {
protocol C;
net {
max-buffers 2048;
ko-count 4;
}
on bailey {
device    /dev/drbd0;
disk      /dev/sda4;
address   192.168.1.125:7789;
meta-disk internal;
}
on giskard {
device    /dev/drbd0;
disk      /dev/sda3;
address   192.168.1.127:7789;
meta-disk internal;
}
}

drbd.conf explained:

Global section, usage-count. The DRBD project keeps statistics about the usage of DRBD versions. They do this by contacting a HTTP server each time a new DRBD version is installed on a system. This can be disabled by setting usage-count no;.

The common seciton contains configurations inhereted by all resources defined.
Setting the syncronisation rate, this is accoimplished by going to the syncer section and then assigning a value to the rate setting. The syncronisation rate refers to rate in which the data is being mirrored in the background. The best setting for the syncronsation rate is related to the speed of the network with which the DRBD systems are communicating on. 100Mbps ethernet supports around 12MBps, Giggabit ethernet somewhere around 125MBps.

in the configuration above, we have a resource defined as r0, the nodes are configured in the "on" host subsections.
"Device" configures the path of the logical block device that will be created by DRBD
"Disk" configures the block device that will be used to store the data.
"Address" configures the IP address and port number of the host that will hold this DRBD device.
"Meta-disk" configures the location where the metadata about the DRBD device will be stored.
You can set this to internal and DRBD will use the physical block device to store the information, by recording the metadata within the last sections of the disk.
Once you have created your configuration file, you must conduct the following steps on both the nodes.

Create device metadata.

$ drbdadm create-md r0
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block sucessfully created.
success

Attach the backing device.
$ drbdadm attach r0

Set the syncronisation parameters.
$ drbdadm syncer r0

Connect it to the peer.
$ drbdadm connect r0

Run the service.
$ service drbd start

Heartbeat:

Heartbeat provides the IP redundancy and the service HA functionailty.
On the failure of the primary node the VIP is assigned to the secondary node and the services configured to be HA are started on the secondary node.

Heartbeat configuration:

/etc/ha/ha.conf

## /etc/ha.d/ha.cf on node1
## This configuration is to be the same on both machines
## This example is made for version 2, comment out crm if using version 1
// replace the node variables with the names of your nodes.

crm no
keepalive 1
deadtime 5
warntime 3
initdead 20
bcast eth0
auto_failback yes
node bailey
node giskard

/etc/ha.d/authkeys
// The configuration below set authentication off, and encryption off for the authentication of nodes and their packets.
//Note make sure the authkeys file has the correct permisisions chmod 600

## /etc/ha.d/authkeys
auth 1
1 crc

/etc/ha.d/haresources
//192.168.1.40 is the VIP (Virtual IP) assigned to the cluster.
//the "smb" in the configuration line represents the service we wish to make HA
// /devdrbd0 represents the resource name you configured in the drbd.conf

## /etc/ha.d/haresources
## This configuration is to be the same on both nodes

bailey 192.168.1.40 drbddisk Filesystem::/dev/drbd0::/drbdData::ext3 smb

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Each Recital table can have one or more data dictionaries to provide a central repository for constraints and other metadata. 

Here's how to set up field validation for a field with a small static number of acceptable values.

Using the example.dbf table from the southwind sample database, validation can be added to the title field to ensure it matches one of a list values.
open database southwind
alter table example add constraint;
(title set check inlist(alltrim(title),"Miss","Mr","Mrs","Ms"))
The inlist() function checks whether the specified expression exists in the comma-separated list which follows.  An attempt to update title with a value not in the list will give an error: Validation on field 'TITLE' failed.

If you have access to the Recital Workbench, you can use the modify structure worksurface to add and alter your dictionary entries, including a customized error message if required.

validation


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This guide will assist you in setting up an rsnapshot backup server on your network. rsnapshot uses rsync via ssh to perform unattended backups of multiple systems in your network. The guide can be found on the centos website here.

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The getUIComponentBitmapData method can create bitmapdata for a given IUIComponent. Pass any UIcomponent to get its respective bitmapdata.

public static function getUIComponentBitmapData(target:IUIComponent):BitmapData {      
    var resultBitmapData:BitmapData = new BitmapData(target.width, target.height);     
    var m:Matrix = new Matrix();     
    resultBitmapData.draw(target, m);     
    return resultBitmapData; 
}

Now convert the bitmapdata to a jpeg bytearray.

private static function encodeToJPEG(data:BitmapData, quality:Number = 75):ByteArray {     
    var encoder:JPGEncoder = new JPGEncoder(quality);     
    return encoder.encode(data); 
}

Now encode the ByteArray into Base64.

public static function base64Encode(data:ByteArray):String {     
    var encoder:Base64Encoder = new Base64Encoder();     
    encoder.encodeBytes(data);     
    return encoder.flush(); 
}

Upload the base64 encoded ByteArray to the server.

public static uploadData():void {     
    var url:String = "saveFile.php";     
    var urlRequest:URLRequest = new URLRequest(url);     
    urlRequest.method = URLRequestMethod.POST;     
    var urlLoader:URLLoader = new URLLoader();     
    var urlVariables:URLVariables = new URLVariables();     
    urlVariables.file = jpgEncodedFile;    // as returned from base64Encode()     
    urlLoader.data = urlVariables;     
    urlLoader.load(urlRequest); 
}

The saveFile.php file on the server.


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Latest Development News

The Lianja Application Platform is a cost-effective cloud database computing platform for SMEs (Small and Medium-sized Enterprises) that lets them focus on developing and deploying business Apps without the need to invest in lengthy application development times and an expensive IT infrastructure.

The three pillars of Lianja are:
  • The Lianja App Builder
  • The Lianja Cloud Database
  • Lianja.com Apps
If you need to develop and deploy cross-platform Visual FoxPRO GUI, Web or Mobile Apps visit the Lianja website for further details.

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Recital 10 introduced the DIE( )and EXIT( ) functions. These functions operates in the same way as the PHP DIE( ) and EXIT( ) functions. They output a message and terminate the current session in both Recital and Recital Web.
try
  open database southwind
catch
  die("Cannot open database, please try later.")
endtry
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