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PACK - what to expect?
Message
De
13/01/2003 13:57:16
 
 
À
13/01/2003 13:48:38
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Divers
Thread ID:
00740999
Message ID:
00741104
Vues:
17
>Jos,
>
>SNIP>
>>>.... And, of course, the Help says that the FPT WILL be handled too, and that in itself might be a major reason some of us run PACK (the better organization being a beneficial side-effect).
>
>I erred as regards PACK MEMO after adding 25,000 memo contents - the FPT was 'optimized' (de-bloated), just not defragmented.
>
>SNIP


I read a really good post on memo fields a while ago but have mislaid my reference to it. (I bet SergeyB knows it :) But an important aspect of memo fields is that when you write data to a memo field it adds that bit of new data to the end of the FPT file and updates its pointers for that record. In this way as data is randomly added to memo fields over time you get bits and pieces of memo data all over the HDD with pointers joining it all together. This does not happen, of course, for a normal fixed length record in a DBF file. Replacing an existing fields contents does not create fragmentation - with memo fields it does.

In addition, old memo data is not removed from the memo field when it is replaced with new data. The old data is still in the FPT file too. So a PACK MEMO does two things (a) remove all the old data and (b) rejoin each memo fields seperate pieces. But still, how this all ends up on the HDD is up to the OS and state of the HDD.
In the End, we will remember not the words of our enemies, but the silence of our friends - Martin Luther King, Jr.
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