************************************* * * * DB/C Newsletter * * November 2000 * * * ************************************* News and Comments DB/C DX 11 was released in November. Response has been excellent, although several bugs have been fixed since the first release. The current release is 11.0.2. Note that the dbcdx.licensekey is unique for each major release of DB/C DX and DB/C FS, thus you will need to obtain the new key when you upgrade from DB/C DX release 10. You can get the software and the new key at the DB/C Online Sales and Update System at www.dbcsoftware.com. This is the first newsletter distributed with our new email list server. The email list server we use is majordomo, which is probably the most popular email list server software. In the past, subscribe and unsubscribe requests have been handled manually. They are now handled automatically by the majordomo software. If you want to find out how majordomo works, send an email to request@dbcsoftware.com that has the word 'help' (without the quotes) in the body of the email. Note that the subject line in the email is ignored. As noted at the end of this newsletter, use the text 'subscribe dbcnews' to subscribe to the DB/C Newsletter and the text 'unsubscribe dbcnews' to unsubscribe from the DB/C Newsletter. If you encounter any problems with majordomo, please let us know. Here is another product description for a commercial application created with DB/C: Infoser BVBA is a Belgian company that has developed BURADEX, an application for administration of a surveyor's office. Most functions of a surveyor's office are automated by BURADEX. A connection to a central database, managed by insurance companies, is provided to allow for calculation of claims using up-to-date prices. The web site is www.infoser.be (in French and Dutch). For information in English, send a request by email to walter.velle@infoser.be. This month's article consists of several new Frequently Asked Questions. As always, these will be added to the FAQ at www.dbcsoftware.com. don.wills@dbcsoftware.com ****************************************************************************** More Frequently Asked Questions Question: What is the file size limit for various versions of DB/C DX? Answer: The maximum file size for text and index files when using the Windows version of DB/C DX 10 and DB/C DX 11 on Windows NT and 2000 (on both client and server) is 1 terabyte. The maximum file size for text and index files using the Windows version of DB/C DX 10 and DB/C DX 11 in other environments is 4 gigabytes, except if the maximum file size of the server operating system is less. The maximum file size for text and index files is 2 gigabytes for all UNIX versions of DB/C DX 10 and DB/C DX 11 except as noted below. For the following versions of DB/C DX 11 the maximum file size is at least 1 terabyte: DB/C DX 11 for Compaq Tru64 UNIX (Alpha chip) DB/C DX 11 for HP UNIX 10.20 DB/C DX 11 for HP UNIX 11.x DB/C DX 11 for IBM AIX 4.3 DB/C DX 11 for SCO Unixware 7 (Intel x86 chip) DB/C DX 11 for Sun Solaris 8 (Sparc chip) For DB/C DX 10, the list is the same as above, except that DB/C DX 10 for Solaris did not support large files. By default, existing licenses of DB/C DX 10 for Solaris that are upgraded to DB/C DX 11 do not get the large file version of DB/C DX 11. Send email to support@dbcsoftware.com to change to the large file version of a license of DB/C DX. ----------------------------------------------------------------------------- Question: In Windows NT and Windows 2000, clients connected with a DB/C FS server run fine when it is started from the command prompt, but when the server runs as a service, all file opens fail with some sort of unable to open error. What is the problem? Answer: The most probable cause is that there was no Log On user specified for the DB/C FS service. The Log On user is specified in the Services Control Panel under the Log On heading. If the default value hasn't been changed, then a local system account with no drive mappings and limited file access is used. The use of drive letters in fully qualified file names is discouraged as it depends on the mappings associated with the Log On user. Use UNC file names instead. UNC file names look like this: \\computer\vol\dir\file ----------------------------------------------------------------------------- Question: When executing an SQL SELECT statement, how does DB/C FS decide whether to use an index, and if so, how does it choose which one to use? Answer: DB/C FS 2 is generally smart about using indexes. If performance can benefit from using an index to satisfy the requirements of the WHERE clause (both JOIN and non-JOIN situations) and/or the ORDER BY clause, then the index will generally be used. If the entire file must be read because the indexes are insufficient, then the text file is read sequentially. There are SELECT statements that are too complex for the DB/C FS SQL engine to optimize successfully. In these cases, the SQL engine falls back to reading the entire file sequentially and then filtering and/or sorting the result. With regard to which index is used - it depends on several factors so no simple answer is available. It is important to understand that the algorithms used by the SQL engine will change between releases of DB/C FS, so that the index files used for a particular query may also change. ----------------------------------------------------------------------------- Question: If a DB/C index was created using a condition (-p parameter), and if DB/C FS 'decides' to use that index for an SQL SELECT statement, are the conditionally selected records the only records visible to the SQL client? Answer: Yes, but your program should not depend on that behavior. The DB/C FS SQL engine doesn't know about indexes created with the -p option. There is an assumption made by the SQL engine that all records of the text file have corresponding index entries in all index files. Thus, if you are using a partial index (whether -p was specified or not), the results of a query depend on whether or not that index is used by the SQL engine. If the index is not used, then all records in the text file that match the conditions of the WHERE clause will be returned. If the index is used, then only those records that match the conditions of the WHERE clause and are found in the index will be returned. Also note that SQL INSERT and UPDATE will change the indexes for all rows that are inserted and updated, regardless of the -p option. ****************************************************************************** DB/C Class Schedule Class: DB/C DX and JX Language Fundamentals Date: January 15-17, 2001 Location: Oak Brook, Illinois For information, contact Judi Tamkevic at: voice 630.572.0240 email admin@dbcsoftware.com ****************************************************************************** Subscribing to the DB/C Newsletter If you don't already have the DB/C Newsletter delivered to your email address and would like to have it emailed to you when it is produced, just send an email message to 'request@dbcsoftware.com' and put the line 'subscribe dbcnews' in the body of the email message (omit the ' characters). The newsletter will be delivered to the email address from which the message was sent. To stop delivery, put the line 'unsubscribe dbcnews' in the body of the message.