In this article Barry Mavin, CEO and Chief Software Architect for Recital, details how to use the Client Drivers provided with the Recital Database Server to work with local or remote server-side OLE DB data sources.
Overview
The Recital Universal .NET Data Provider provides connectivity to the Recital Database Server running on any supported platform (Windows, Linux, Unix, OpenVMS) using the RecitalConnection object.
The Recital Universal JDBC Driver provides the same functionality for java applications.
The Recital Universal ODBC Driver provides the same functionality for applications that use ODBC.
Each of the above Client Drivers use a connection string to describe connections parameters.
The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equal sign (=) connects each keyword and its value.
The following table lists the valid names for keyword/values.
Name | Default | Description |
---|---|---|
Data Source
|
The name or network address of the instance of the Recital Database Server which to connect to. | |
Directory | The target directory on the remote server where data to be accessed resides. This is ignored when a Database is specified. | |
Encrypt |
false | When true, DES3 encryption is used for all data sent between the client and server. |
Initial Catalog -or- Database |
The name of the database on the remote server. | |
Password -or- Pwd |
The password used to authenticate access to the remote server. | |
User ID | The user name used to authenticate access to the remote server. | |
Connection Pooling |
false | Enable connection pooling to the server. This provides for one connection to be shared. |
Logging | false | Provides for the ability to log all server requests for debugging purposes |
Rowid | true | When Rowid is true (the default) a column will be post-fixed to each SELECT query that is a unique row identifier. This is used to provide optimised UPDATE and DELETE operations. If you use the RecitalSqlGrid, RecitalSqlForm, or RecitalSqlGridForm components then this column is not visible but is used to handle updates to the underlying data source. |
Logfile | The name of the logfile for logging | |
Gateway |
Opens an SQL gateway(Connection) to a foreign SQL data source on the remote server. Using Gateways, you can transparently access the following local or remote data sources:
The gateway can be specified in several formats: servertype@nodename:username/password-database e.g. oracle@nodename:username/password-database mysql@nodename:username/password-database postgresql@nodename:username/password-database -or- odbc:odbc_data_source_name_on_server oledb:oledb_connection_string_on_server jdbc:jdbc_driver_path_on_server;jdbc:Recital:args |
To connect to a server-side OLE DB data source, you use the gateway=value key/value pair in the following way.
gateway=oledb:oledb_connection_string_on_server
ImportantWhen specifying the connection string be sure to quote the gateway= with "...".
You can find examples of connection strings for most ODBC and OLE DB data sources by clicking here.
Example in C# using the Recital Universal .NET Data Provider:
//////////////////////////////////////////////////////////////////////// // include the references below using System.Data; using Recital.Data; //////////////////////////////////////////////////////////////////////// // The following code example creates an instance of a DataAdapter that // uses a Connection to the Recital Database Server, and a gateway to // the SQL server Northwind database. It then populates a DataTable // in a DataSet with the list of customers. The SQL statement and // Connection arguments passed to the DataAdapter constructor are used // to create the SelectCommand property of the DataAdapter. public DataSet SelectCustomers() { string gateway = "oledb:Provider=sqloledb;Initial Catalog=Northwind; Data Source=localhost;Integrated Security=SSPI"; RecitalConnection swindConn = new RecitalConnection("Data Source=localhost;gateway=\""+gateway+"\"); RecitalCommand selectCMD = new RecitalCommand("SELECT CustomerID, CompanyName FROM Customers", swindConn); selectCMD.CommandTimeout = 30; RecitalDataAdapter custDA = new RecitalDataAdapter(); custDA.SelectCommand = selectCMD; swindConn.Open(); DataSet custDS = new DataSet(); custDA.Fill(custDS, "Customers"); swindConn.Close(); return custDS; }
Example in Java using the Recital Universal JDBC Driver:
//////////////////////////////////////////////////////////////////////// // standard imports required by the JDBC driver import java.sql.*; import java.io.*; import java.net.URL; import java.math.BigDecimal; import Recital.sql.*; //////////////////////////////////////////////////////////////////////// // The following code example creates a Connection to the Recital // Database Server, and a gateway to the SQL server Northwind database. // It then retrieves all the customers. public void SelectCustomers() { // setup the Connection URL for JDBC String gateway = "oledb:Provider=sqloledb;Initial Catalog=Northwind; Data Source=localhost;Integrated Security=SSPI"; String url = "jdbc:Recital:Data Source=localhost;gateway=\""+gateway+"\"; // load the Recital Universal JDBC Driver new RecitalDriver(); // create the connection Connection con = DriverManager.getConnection(url); // create the statement Statement stmt = con.createStatement(); // perform the SQL query ResultSet rs = stmt.executeQuery("SELECT CustomerID, CompanyName FROM Customers"); // fetch the data while (rs.next()) { String CompanyID = rs.getString("CustomerID"); String CompanyName = rs.getString("CompanyName"); // do something with the data... } // Release the statement stmt.close(); // Disconnect from the server con.close(); }
We are pleased to announce the immediate availability of Recital 10.0.1.
Included in this version are:
- Improved SQL query optimizer
- *New* apache plugin for building Recital web apps on x86_64 (mod_recital64.so)
- Performance improvements in connections to Recital Server and Recital Web.
- Recital ODBC driver performance improvements and bug fixes
- Miscellaneous bug fixes
Existing Recital 10 users can download the patch file and apply it to an existing installation.
Enjoy!
The 64bit port of Recital requires these libraries to allow access to 32bit Xbase and C-ISAM data files which are 32bit.
If you do not have these libraries installed you will either get a "can't find db.exe" or an "error loading shared libraries" when trying to run or license Recital.
Installing the ia32 shared libraries
Redhat EL 5 / Centos 5 / Fedora 10
-
Insert the Red Hat Enterprise Linux 5 Supplementary CD, which contains the ia32el package.
-
After the system has mounted the CD, change to the directory containing the Supplementary packages. For example:
cd /media/cdrom/Supplementary/
-
Install the ia32el package:
rpm -Uvh ia32el-<version>.ia64.rpm
yum install ia32el
Ubuntu / Debian
sudo apt-get install ia32-libs
This article discusses Recital database security: from operating system file permissions through file and field protection to DES3 encryption.
Overview
A company's data is extremely valuable and must be protected, both in operation and in physical file format. Recital products provide a range of ways to protect your data.
Operating System File Permissions
The most basic level of database security is provided by the operating system. Recital database tables and indexes are individual files with their own respective operating system file permissions. Read permission is required to open a table and write permission to update a table. If a user does not have read permission they are denied access. Without write permission, a table will be opened read-only.
Here the owner, root, and members of the recital group have write permission, so can update the example table unless additional protection applies. Other users can only open the example table read-only.
# ls -l example* -rwxrwxr-x 1 root recital 147 Nov 29 14:27 example.dbd -rwxrwxr-x 1 root recital 41580 Nov 29 14:27 example.dbf -rwxrwxr-x 1 root recital 13312 Nov 29 14:28 example.dbt -rwxrwxr-x 1 root recital 19456 Nov 29 14:28 example.dbx
Note: As in the example above, a table's associated files should have the same permissions as the table itself:
File Extension |
File Type |
.dbd |
Dictionary |
.dbf |
Table |
.dbt |
Memo |
.dbx |
Index |
Database Dictionary
Each Recital table may have a Database Dictionary. The Dictionary can be used both to protect the integrity of the data and to protect access to the data. This section covers Column Constraints, Triggers, Security and Protection.
Column Constraints: Data Integrity
The Dictionary attributes or constraints either prevent the entry of incorrect data, e.g. must_enter and validation or aid the entry of correct data, e.g. default, picture and choicelist. The Dictionary can be modified in the character mode CREATE/MODIFY STRUCTURE worksurface, via SQL statements, or in the Recital Enterprise Studio Database Administrator.
Click image to display full size
Fig 1: MODIFY STRUCTURE Worksurface: Dictionary.
The SQL Column Constraints are as follows:
Constraint |
Description |
AUTO_INCREMENT | AUTOINC |
Used to auto increment the value of a column. |
CALCULATED |
Used to calculate the value of a column. |
CHECK | SET CHECK |
Used to validate a change to the value of a column. |
DEFAULT |
Used to set a default value for the specified column. |
DESCRIPTION |
Used set the column description for the specified column. |
ERROR |
Used to define an error message to be displayed when a validation check fails. |
FOREIGN KEY |
Used to define a column as a Foreign Key for a parent table. |
NOCPTRANS |
Used to prevent code page translation for character and memo fields. |
NOT NULL | NULL |
Used to disallow/allow NULL values. |
PRIMARY KEY |
Used to define a tables Primary Key. |
RANGE |
Used to specify minimum and maximum values for a date or numerical column. |
RECALCULATE |
Used to force recalculation of calculated columns when a columns value changes. |
REFERENCES |
Used to create a relationship to an index key of another table. |
UNIQUE |
Used to define the column as a candidate index for the table |
These can be specified in CREATE TABLE or ALTER TABLE statements:
exec sql OPEN DATABASE southwind; exec sql ALTER TABLE customers ADD COLUMN timeref char(8) CHECK validtime(timeref) ERROR "Not a valid time string";
Click image to display full size
Fig 2: Database Administrator: Column Constraints and Attributes.
TRIGGERS
Table Level Triggers are event-driven procedures called before an I/O operation. These can be used to introduce another layer of checks before a particular operation is permitted to take place or to simply set up logging of those operations.
The CREATE/MODIFY STRUCTURE worksurface <TRIGGERS> menu bar option allows you to specify table level triggers. You may edit a trigger procedure from within the <TRIGGERS> menu by placing the cursor next to the procedure name and pressing the [HELP] key. A text window pops up for editing. If the table triggers are stored in separate <.prg> files, rather than in a procedure library, procedures need not be predefined (SET PROCEDURE) before using the table.
Click image to display full size
Fig 3: MODIFY STRUCTURE Worksurface: Triggers.
The following triggers can be selected and associated with a specified procedure name in the <TRIGGERS> menu.
Trigger |
Description |
UPDATE |
The specified procedure is called prior to an update operation on the table. If the procedure returns .F., then the UPDATE is canceled. |
DELETE |
The specified procedure is called prior to a delete operation on the table. If the procedure returns .F., then the DELETE is canceled. |
APPEND |
The specified procedure is called prior to an append operation on the table. If the procedure returns .F., then the APPEND is canceled. |
OPEN |
The specified procedure is called after an open operation on the table. |
CLOSE |
The specified procedure is called prior to a close operation on the table. |
ROLLBACK |
The specified procedure is called when a user presses the [ABANDON] key in a forms based operation. |
The Recital Enterprise Studio Database Administrator also allows you to associate existing programs as Table Trigger Procedures.
Click image to display full size
Fig 4: Database Administrator: Triggers.
Programmatically, Trigger Procedures can also be associated with a table using SQL. The following table constraints may be applied in the SQL CREATE TABLE and ALTER TABLE statements:
Trigger |
Description |
ONUPDATE |
The specified procedure is called prior to an update operation
on the table. If the procedure returns .F., then the UPDATE
is canceled. |
ONDELETE |
The specified procedure is called prior to a delete operation
on the table. If the procedure returns .F., then the DELETE
is canceled. |
ONINSERT |
The specified procedure is called prior to an insert operation
on the table. If the procedure returns .F., then the INSERT
is canceled. |
ONOPEN |
The specified procedure is called after an open operation
on the table. |
ONCLOSE |
The specified procedure is called prior to a close operation
on the table. |
ONROLLBACK |
The specified procedure is called when a user presses the
[ABANDON] key in a forms based operation. |
SECURITY
As mentioned above, all Recital files are subject to Operating System read and write permissions. These permissions can be further refined, while still using the Operating System user and group IDs, in the Security and Protection sections of the Dictionary. The Security section handles table based operations and the Protection section focuses on individual fields.
Security and Protection rules can be defined in the CREATE/MODIFY STRUCTURE worksurface of Recital Terminal Developer, via the SQL GRANT and REVOKE statements or in the Recital Enterprise Studio Database Administrator.
Click image to display full size
Fig 5: MODIFY STRUCTURE Worksurface: Security.
The Security section has table operations for which Access Control Strings can be specified. An Access Control String (ACS) is a range of valid user identification codes, and is used to restrict table operations to certain individuals or groups. Each user on the system is allocated a group number and a user number. The user identification code is the combination of group and user numbers. When constructing an Access Control String of linked user identification codes, wild card characters may be used.
Example ACS |
Description |
[1,2] |
In group 1, user 2 |
[100,*] |
In group 100, all users |
[2-7,*] |
In groups 2-7, all users |
[*,100-200] |
In all groups, users 100-200 |
[1,*]&[2-7,1-7] |
In group 1, all users, in groups 2-7, users 1-7 |
Please note that the maximum ACS length is 254 characters. OpenVMS group and user numbers are stored and specified in octal. On other Operating Systems, group and user numbers are stored and specified in decimal.
Access Control Strings may be associated with the following operations:
Operation |
Description |
READONLY |
Users specified in the ACS have read-only access to the table. All other users have update access. |
UPDATE |
Users specified in the ACS have update access to the table. All other users are restricted to read-only access. |
APPEND |
Users specified in the ACS can append records into the table. No other users can append. |
DELETE |
Users specified in the ACS can delete records from the table. No other users can delete. |
COPY |
Users specified in the ACS can copy records from the table. No other users can copy. |
ADMIN |
Users specified in the ACS can use the following commands: |
The corresponding SQL privileges are:
Operation |
Description |
SELECT |
Users specified in the ACS may name any column in a SELECT statement. All other users have update access. |
UPDATE |
Users specified in the ACS may name any column in an UPDATE statement. All other users are restricted to read-only access. |
INSERT |
Users specified in the ACS can INSERT rows into the table. No other users can INSERT. |
DELETE |
Users specified in the ACS can DELETE rows from the table. No other users can DELETE. |
ALTER |
Users specified in the ACS can use the ALTER TABLE statement on this table. |
READONLY |
Users specified in the ACS may read any column in a SELECT statement. All other users have update access. |
// Grant insert privilege for the customer table exec sql OPEN DATABASE southwind; exec sql GRANT UPDATE (lastname, firstname) INSERT ON customers TO '[20,100]'; // Grant all privileges to all users exec sql OPEN DATABASE southwind; exec sql GRANT ALL ON shippers TO PUBLIC;
PROTECTION
Security and Protection rules can be defined in the CREATE/MODIFY STRUCTURE worksurface of Recital Terminal Developer, via the SQL GRANT and REVOKE statements or in the Recital Enterprise Studio Database Administrator.
Click image to display full size
Fig 6: Database Administrator: Protection.
The format of the ACS is the same as in <SECURITY> above.
The following protection can be defined:
Operation |
Description |
READONLY |
Users specified in the ACS have read-only access to the field. All other users have update access. |
UPDATE |
Users specified in the ACS have update access to the field. All other users are restricted to read-only access. |
Recital Terminal Developer also has 'HIDDEN' Protection:
Operation |
Description |
HIDDEN |
Users specified in the ACS see the 'hiddenfield'character rather than the data in the field. All other users see the data. |
Hidden fields can be accessed and viewed on a work surface, but the field contains the hiddenfield character, ?. If the field is referenced in an expression, it will contain the following: blanks for character fields, F for logical fields, 00/00/0000 for date fields and blank for memo fields.
The corresponding SQL privileges are:
Operation |
Description |
SELECT |
Users specified in the ACS may name the column in a SELECT statement. All other users have update access. |
UPDATE |
Users specified in the ACS may name the column in an UPDATE statement. All other users are restricted to read-only access. |
READONLY |
Users specified in the ACS may read the column in a SELECT statement. All other users have update access. |
// Grant update privilege for columns lastname and firstname from the customer table exec sql OPEN DATABASE southwind; exec sql GRANT UPDATE (lastname, firstname) customers TO '[20,100]';
Encryption
From Recital 8.5 onwards, Recital installations that have the additional DES3 license option have the ability to encrypt the data held in Recital database tables. Once a database table has been encrypted, the data cannot be accessed unless the correct three-part encryption key is specified, providing additional security for sensitive data.
ENCRYPT
The ENCRYPT Recital 4GL command is used to encrypt the data in the specified table or tables matching a skeleton. If the skeleton syntax is used, then all matching tables will be given the same encryption key. The encryption key is a three part comma-separated key and may optionally be enclosed in angled brackets. Each part of the key can be a maximum of 8 characters. The key is DES3 encrypted and stored in a .dkf file with the same basename as the table. After encryption, the three parts of the key must be specified correctly before the table can be accessed.
// Encrypt individual tables encrypt customers key "key_1,key_2,key_3" encrypt employees key "<key_1,key_2,key_3>" // Encrypt all .dbf files in the directory encrypt *.dbf key "key_1,key_2,key_3"
SET ENCRYPTION
If a database table is encrypted, the correct three-part encryption key must be specified before the table's data or structure can be accessed. The SET ENCRYPTION TO set command can be used to specify a default encryption key to be used whenever an encrypted table is accessed without the key being specified. The encryption key is a three part comma-separated key.
If the command to access the table includes the key, either by appending it to the table filename specification or using an explicit clause, this will take precedence over the key defined by SET ENCRYPTION TO.
Issuing SET ENCRYPTION TO without a key causes any previous setting to be cleared. The key must then be specified for each individual encrypted table.
The default key defined by SET ENCRYPTION is only active when SET ENCRYPTION is ON. SET ENCRYPTION OFF can be used to temporarily disable the default key. The SET ENCRYPTION ON | OFF setting does not change the default key itself. SET ENCRYPTION is ON by default.
// Encrypt individual tables encrypt customers key "key_1,key_2,key_3" encrypt shippers key "key_2,key_3,key_4" // Specify a default encryption key set encryption to "key_1,key_2,key_3" // Open customers table using the default encryption key use customers // Specify shippers table's encryption key use shippers<key_2,key_3,key_4> // Disable the default encryption key set encryption to // Specify the individual encryption keys use customers encryption "key_1,key_2,key_3" use shippers<key_2,key_3,key_4>
DECRYPT
The DECRYPT command is used to decrypt the data in the specified table or tables matching a skeleton. The specified key must contain the three part comma-separated key used to previously encrypt the table and may optionally be enclosed in angled brackets. The skeleton syntax can only be used if all tables matching the skeletonhave the same key.
The DECRYPT command decrypts the data and removes the table’s .dkf file. After decryption, the key need no longer be specified to gain access to the table.
// Decrypt individual tables decrypt customers key "key_1,key_2,key_3" decrypt employees key "<key_1,key_2,key_3>" // Decrypt all .dbf files in the directory decrypt *.dbf key "key_1,key_2,key_3"
All of the following commands are affected when a table is encrypted:
- APPEND FROM
- COPY FILE
- COPY STRUCTURE
- COPY TO
- DIR
- USE
- SQL INSERT
- SQL SELECT
- SQL UPDATE
APPEND FROM
Used to append records to the active table from another table.// The key must be specified for an encrypted source table
use mycustomers append from customers encryption "key_1,key_2,key_3"; for country = "UK"
COPY FILE
Used to copy a file.// The key file must also be copied for an encrypted source table // as the target table will be encrypted
encrypt customers key "key_1,key_2,key_3" copy file customers.dbf to newcustomers.dbf copy file customers.dkf to newcustomers.dkf use newcustomers encryption "key_1,key_2,key_3"
COPY STRUCTURE
Used to copy a table's structure to a new table.// The key file is automatically copied for an encrypted source table // and the target table encrypted
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3" copy structure to blankcust use blankcust encryption "key_1,key_2,key_3"
COPY TO
Used to copy a table.// By default, the key file is automatically copied for an encrypted // source table and the target table encrypted with the same key encrypt customers key "key_1,key_2,key_3" use customers encryption "key_1,key_2,key_3" copy to newcustomers use newcustomers encryption "key_1,key_2,key_3" // You can also create a copy with a different key encrypt customers key "key_1,key_2,key_3" use customers encryption "key_1,key_2,key_3" copy to newcustomers encrypt "newkey_1,newkey_2,newkey_3" use newcustomers encryption "newkey_1,newkey_2,newkey_3" // Or create a decrypted copy encrypt customers key "key_1,key_2,key_3" use customers encryption "key_1,key_2,key_3" copy to newcustomers decrypt use newcustomers // You can also create an encrypted copy of a non-encrypted source table use orders copy to encorders encrypt "newkey_1,newkey_2,newkey_3" use encorders encryption "newkey_1,newkey_2,newkey_3"
DIR
Used to display a directory listing of tables.// Encrypted tables are flagged as such with (DES3) > open database southwind > dir
Current database: southwind Tables # Records Last Update Size Dictionary Triggers Security categories.dbf 8 01/10/06 24576 None None None cisamdemo.dbf ---> CISAM/Bridge [cisamdemo] customers.dbf (DES3) 91 05/12/04 49600 None None None employees.dbf 9 05/12/04 25520 None None None example.dbf (DES3) 100 12/24/05 38080 Yes Yes None order_details.dbf 2155 05/12/04 296320 None None None orders.dbf 829 05/12/04 232704 None None None products.dbf 77 05/12/04 37112 None None None productsbyname.dbf 77 05/12/04 29104 None None None shippers.dbf (DES3) 3 05/12/04 20864 None None None suppliers.dbf 29 12/08/05 29992 Yes None None 0.765 MB in 11 files. 1.093 GB remaining on drive.
USE
Used to open a table.// The three part key must be specified to open an // encrypted table. All of the following are valid. // 1. Specifying a default encryption key before opening the table set encryption to "key_1,key_2,key_3" use customers // 2. Appending the key to the filename use customers<key_1,key_2,key_3> // 3. Using the ENCRYPTION clause, optionally specifying angled brackets use customers encryption "key_1,key_2,key_3" use customers encryption "<key_1,key_2,key_3>"
SQL INSERT
Used to add a row to a table via SQL.// The three part key can be specified using a // default encryption key before opening the table exec sql OPEN DATABASE southwind; exec sql SET ENCRYPTION TO "key_1,key_2,key_3"; exec sql INSERT INTO customers (customerid, companyname) VALUES ('RECIT','Recital Corporation'); // Or by appending the key to the filename exec sql OPEN DATABASE southwind; exec sql INSERT INTO customers<key_1,key_2,key_3> (customerid, companyname) VALUES ('RECIT','Recital Corporation');
SQL SELECT
Used to return data from a table via SQL.// The three part key can be specified using a // default encryption key before opening the table exec sql OPEN DATABASE southwind; exec sql SET ENCRYPTION TO "key_1,key_2,key_3"; exec sql SELECT * FROM customers; // Or by appending the key to the filename exec sql OPEN DATABASE southwind; exec sql SELECT * FROM customers<key_1,key_2,key_3>;
SQL UPDATE
Used to update data in a table via SQL.// The three part key can be specified using a // default encryption key before opening the table exec sql OPEN DATABASE southwind; exec sql SET ENCRYPTION TO "key_1,key_2,key_3"; exec sql UPDATE customers SET companyname='Recital Corporation Inc.' WHERE customerid='RECIT'; // Or by appending the key to the filename exec sql OPEN DATABASE southwind; exec sql UPDATE customers<key_1,key_2,key_3> SET companyname='Recital Corporation Inc.' WHERE customerid='RECIT';
Summary
Recital offers a range of ways to keep your data secure. These start with the Operating System read/write permissions, which can be further refined to the level of table I/O operations and then field access in the Dictionary based Security and Protection rules. The Dictionary also provides the means to protect the integrity of the data via data validation and to assist in correct data entry through the use of choicelists, help messages and picture clauses etc. A further role of the Dictionary is in the provision of Table Triggers, which can be used to enable a programmatic response to table operations to add in additional checks or audit trails. For the most sensitive data, DES3 encryption is the ultimate protection: encrypting the physical data on the disk and only permitting table access on the production of the three part encryption key.
In this article Barry Mavin, CEO and Chief Software Architect for Recital, gives details on Working with user-defined Functions in the Recital Database Server.
Overview
User-defined functions (UDFs) are collections of statements written in the Recital 4GL (compatible with Visual FoxPro) stored under a name and saved in a Database. User-defined functions are just-in-time compiled by the Recital database engine. User-defined functions can be used in SQL statements to extend the power and flexibility of the inbuilt functions. Using the Database Administrator in Recital Enterprise Studio, you can easily create, view, modify, and test Stored Procedures, Triggers, and user-defined functions.
Tip
You can also extend the Recital Database Server with C Extension Libraries and use the functions defined within that library also.Creating and Editing user-defined functions
To create a new User-defined function, right-click the Procedures node in the Databases tree of the Project Explorer and choose Create. To modify an existing User-defined function select the User-defined function in the Databases Tree in the Project Explorer by double-clicking on it or selecting Modify from the context menu. By convertion we recommend that you name your User-defined functions beginning with "f_xxx_", where xxx is the name of the table that they are associated with.
Testing the user-defined function
To test run the user-defined function, select it in the Databases Tree in the Project Explorer by double-clicking on it. Once the Database Administrator is displayed, click the Run button to run it.
Example
Example: user-defined function "f_order_details_total".
//////////////////////////////////////////////////////////////////////// // example user-defined function function f_order_details_total(pUnitprice, pQuantity, pDiscount) return (pUnitprice + pQuantity + pDiscount) > 0 endfunc
Example: using the user-defined function in a SQL SELECT statement.
//////////////////////////////////////////////////////////////////////// // sample code to use a user-defined function in a SQL SELECT statement select * from customers where f_order_details_total(Unitprice, Quantity, Discount)
Using user-defined function libraries with the Recital Database Server
You can place all of the user-defined functions associated with a particular table into a procedure library. You then define an Open Trigger for the table that opens up the procedure library whenever the table is accessed. This is a much faster way of using user-defined functions as it reduces the amount of file open/close operations during a query and also simplifies development and maintenance.
By convertion we recommend that you should name the library using the convention "lib_xxx", where xxx is the name of the table that the library is associated with.
Example: procedure library in lib_order_details.
//////////////////////////////////////////////////////////////////////// // example user-defined functions function f_order_details_total(pUnitprice, pQuantity, pDiscount) return (pUnitprice * pQuantity - pDiscount) > 0 endfunc function f_order_details_diff(pUnitprice, pQuantity, pDiscount, pValue) return f_order_details_total(pUnitprice, pQuantity, pDiscount) - pValue endfunc
Example: Open Trigger in dt_order_details_open.
//////////////////////////////////////////////////////////////////////// // This trigger will open up the procedure library when the table is opened set procedure to lib_order_details additive
Example: Close Trigger in dt_order_details_close.
//////////////////////////////////////////////////////////////////////// // This trigger will close the procedure library when the table is closed close procedure lib_order_details
Example: using the user-defined function in a SQL SELECT statement.
//////////////////////////////////////////////////////////////////////// // sample code to use a user-defined function in a SQL SELECT statement select * from customers where f_order_details_total(Unitprice, Quantity, Discount)
User-defined functions can also be used with any of the Client Drivers that work with the Recital Database Server.
System Requirements:
- Minimum memory: 4MB
- Minimum Diskspace: ~20MB
MQCURMSGS()
Syntax
MQCURMSGS( <expN> )Description
The MQCURMSGS() function returns the current number of unread messages in the queue specified by <expN>Example
mqdes=mqopen("/myqueue") if (mqdes < 0) messagebox(strerror()+",errno="+alltrim(str(error()))) return endif do while (mqcurmsgs(mqdes) > 0) mstr=mqreceive(mqdes) if (empty(mstr)) messagebox(strerror()+",errno="+alltrim(str(error()))) return endif messagebox(mstr) end do mqclose(mqdes)
alias pwd "? default()" alias cp "copy file " alias mv "rename " alias rm "erase " alias ls "run('ls $0')" alias ps "run('ps $0')" alias grep "run('grep $0')" alias cd "set default to $1" alias cls "clear screen"These commands can now be used inside the Recital command window just as you would use them at the linux prompt, including the ability to pipe commands together.
ls -l | grep .prg ps -elf | grep db.exeThe run() function that is used to run the shell command as specified in the alias command will capture output and display it in a text viewer. If you want to run the command and display the contents full screen, then specify true as the third parameter to the run().
run("command", true, true)
Argument | Description |
---|---|
1 | the command line to run |
2 | True if output should be displayed in a text area (default True) |
3 | True if the output should be displayed full screen (default False) |
Macro | Description |
---|---|
$0 | the command line following the command name |
$1..$n | the arguments given to the command |
Some options of hdparm are dangerous and are generally listed as such in the man page.
Hdparm is available from SourceForge and there is even a version for Windows.
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!