80-Bus News

  

Spring 1985, Volume 4, Issue 1











Page 7 of 31











THE DH BITS by Dave Hunt

In this section of miscellaneous ramblings, the always verbose David Hunt looks at copying files via dBASEIl, changes that have occurred in different versions of dBASEIl, disk sector skewing, disk blocking/deblocking, how to expand a Nascom based system, a tip on using the Pretzel program, and a look at the Gateway and Pathway programs.

Speeding up dBASE Ilusing RAM-disks

Following on from my other article concerning adding machine code patches to dBASEIl, a new routine has had to be written lately. So this bit is for dBASE aficionados, although it contains a warning for all who would write simple file copying routines.

Now those who know dBASE will know the geriatric performance it puts in when indexing files with a good few thousand records. Far too slow on a floppy disk, somewhat better on a Winnie and just reasonable on a RAM disk. Further, versions of dBASE earlier than V2.41 get very slow when updating files with multiple indexes.

An aside about dBASE V2.41

By the way, dBASE V2.41 has what appears to be horrific change of philosophy which I believe has led to its rapid replacement with the current version, V2.43, so anyone with version 2.41, watch out when trying the following:

@ x,y GET input

READ

FIND &input

DO WHILE input=record (... do your thing ...} SKIP

ENDDO

What all versions of dBASE, except V2.41 do, is that the FIND function finds the first occurrence of the find criteria, whilst the DO WHILE – SKIP loop then finds all following entries where the input and record criteria match, the loop cops out when the ‘criteria no longer match. Basically it works through a matching list in order of entry until it no longer matches. V2.41 is something different. Using the same routine, the FIND will find the first occurrence as before, but for some unexplained reason, it then sets the record pointer to the end of the list, so the following DO WHILE – SKIP loop will immediately find the next record does not match and cop out. The way round it is to rewrite the program:

@ x,y GET input

READ

FIND &input

DO WHILE input=record (... do your thing ...) SKIP -1

ENDDO

In this case it appears to almost work backwards through the list (almost, as the first record found is still the first in the list), not a disaster, and in many ways more convenient as it’s more often than not the last in the list you’re looking for, not the first. But what about all the programs written for other versions of dBASE, they’re incompatible!!

To tell the truth I didn’t find this, Trevor at ACC did, when it screwed up an invoicing program I had written. He phoned me to discover what special feature it was that I’d added to the latest version of the program that didn’t work. I started investigating! I assumed this was a new feature of V2.41, and you now had the option for either backwards or forwards search (very useful), but I could find no reference to it in the manual and no way of switching back to ‘normal’. As I said, V2.43 followed hot on the heals of V2.41, and that works ‘normally’, so perhaps the V2.41 anomaly was considered as a bug. To be fair, I only had one copy of V2.41 to test, and this was replaced with V2.43, so perhaps it was a corrupt disk or something, although I’ve yet to hear of a corrupt disk causing a complete change in philosophy, corrupt disks usually crash.

And so back to the indexing problem.

Now lets take the real life situation, it’s a stock control program working on a Gemini with a 10M Winnie. The main stock file has something like 2000 records in it and the transaction file has about 6000 and increases with each stock movement. The stock file has three indexes all on at once, whilst the transaction record is indexed by date and the paperwork reference number. Believe me there’s some index churning going on. Given that indexing is pretty fast in a RAM disk, the problem is getting the indexes there safely.

One way round is to copy the files to the RAM disk before operating the dBASE program, and then copying them back on close down, you’ll away remember to do it, won’t you??!1? But what about the idiots who usually use the program, they’ll either forget to copy the indexes first in which case the programs won’t work, or worse, they’ll forget to copy them back when they’ve finished. Another way would be to reindex the programs onto the RAM disk each time the program’s started, Ok, and no need to copy the files back. But even with a RAM disk, the reindexing process takes some time. I suppose the whole program could be run under a


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