Access table, data lost

When taking a regular back-up copy I noticed that the size of my database had 
halved, from 47MB to 23.5MB without any apparent loss of data.
I now see that one table is approximately 25% of its original size , where 
the list of names now only reaches "B" instead of "Z" as before?
0
Utf
9/7/2007 9:24:08 AM
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Ouch! You may have actually lost data, or you could be lucky. This can occur 
when an index goes bad. If so, you may be able to rescue the data by 
deleting the index, and re-creating it.

Details in the 2nd symptom in this article:
    http://allenbrowne.com/ser-47.html#NumberOfRecordsVaries

Be sure to make a copy of the database before doing anything else. This 
gives you multiple chances to try to rescue it.

-- 
Allen Browne - Microsoft MVP.  Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

"Rocket Ron" <Rocket Ron@discussions.microsoft.com> wrote in message
news:C7F04B1B-F836-4738-81FA-16E99DC8E479@microsoft.com...
> When taking a regular back-up copy I noticed that the size of my database 
> had
> halved, from 47MB to 23.5MB without any apparent loss of data.
> I now see that one table is approximately 25% of its original size , where
> the list of names now only reaches "B" instead of "Z" as before? 

0
Allen
9/7/2007 10:40:48 AM
You asked, What's meant by index?

An index is a set of pointers to your records. All databases use them, so 
they can locate records instantly. Before computers, you could go to any 
library and find 3 indexes for the books: one by author, one by title, and 
one by topic. They were literally index cards. You could look up an author, 
and find the key value (e.g. the Dewey number) that indicated where the book 
was physically stored, and so find the book without having to look through 
every shelf in the library.

In table design view in Access, each field has a property called Indexed (in 
the lower pane.) If you choose Yes, Access maintains an index on this field. 
Now if you sort by this field, or search on this field, Access can find the 
value instantly without having to scan the entire table to find the match.

For the sake of performance, these indexes are maintained in RAM, and only 
written to the disk periodically. If the power goes off during a write, the 
index can contain invalid or incomplete data. A symptom of this can be that 
the index only goes as far as B, so all the later records appear to be 
missing when Access is using this index. However, if you sort differently, 
so Access uses another index, all the records suddenly turn up again.

All databases uses indexes, and there is always a way to tell them to 
rebuild their indexes. In Access, that's part of what the "repair" does 
under:
    Tools | Database Utilities | Compact/Repair

Sometimes it takes a bit more than that to fix the index, particularly where 
other tables are connecting to this one based on that index. The article 
explains how to handle those steps.

Of course, it is also possible that something else went wrong, e.g. the data 
was actually deleted by someone, or a pointer to the actual data went bad, 
or your disk sectors are cross linked. But the problem with the index is 
more likely, so fingers crossed.

-- 
Allen Browne - Microsoft MVP.  Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

"Rocket Ron" <RocketRon@discussions.microsoft.com> wrote in message
news:3F6E966C-CE79-4F42-A779-55F1937DE8D6@microsoft.com...
> Thanks Allen
> I always take a manual back-up copy and there is a mirrored external
> hard-drive set-up. It's since this installation that I have found the 
> problem.
> I will study your suggestions and advise in due course, I have already
> adjusted from the back-up so lucky so far. Must check what is meant by 
> index.
> Thanks again.
>
> "Allen Browne" wrote:
>
>> Ouch! You may have actually lost data, or you could be lucky. This can 
>> occur
>> when an index goes bad. If so, you may be able to rescue the data by
>> deleting the index, and re-creating it.
>>
>> Details in the 2nd symptom in this article:
>>     http://allenbrowne.com/ser-47.html#NumberOfRecordsVaries
>>
>> Be sure to make a copy of the database before doing anything else. This
>> gives you multiple chances to try to rescue it.
>>
>> "Rocket Ron" <Rocket Ron@discussions.microsoft.com> wrote in message
>> news:C7F04B1B-F836-4738-81FA-16E99DC8E479@microsoft.com...
>> > When taking a regular back-up copy I noticed that the size of my 
>> > database
>> > had
>> > halved, from 47MB to 23.5MB without any apparent loss of data.
>> > I now see that one table is approximately 25% of its original size , 
>> > where
>> > the list of names now only reaches "B" instead of "Z" as before? 

0
Allen
9/8/2007 2:21:33 AM
Allen
Thanks again for your reply which I find very interesting. I will be looking 
into all that you have told me when I go back to work on Monday morning, I 
won't have too much time over the weekend.
After I retired, 4 years ago, I started to work part-time for my son-in-law. 
I was studying Access as an interest, again part-time, when Steve asked me to 
use my "knowledge" to help him in his business. Of course, once I started to 
use Access daily, I didn't get the time to further my knowledge but have 
become quite proficient with what I already know. 
I had intended to continue the course but "pressures" of grandchildren etc 
have proved overwhelming.
Anyway, just some background info, I will keep you up-to-date later, thanks 
again.
Regards, Ron (what does MVP stand for?) 

"Allen Browne" wrote:

> You asked, What's meant by index?
> 
> An index is a set of pointers to your records. All databases use them, so 
> they can locate records instantly. Before computers, you could go to any 
> library and find 3 indexes for the books: one by author, one by title, and 
> one by topic. They were literally index cards. You could look up an author, 
> and find the key value (e.g. the Dewey number) that indicated where the book 
> was physically stored, and so find the book without having to look through 
> every shelf in the library.
> 
> In table design view in Access, each field has a property called Indexed (in 
> the lower pane.) If you choose Yes, Access maintains an index on this field. 
> Now if you sort by this field, or search on this field, Access can find the 
> value instantly without having to scan the entire table to find the match.
> 
> For the sake of performance, these indexes are maintained in RAM, and only 
> written to the disk periodically. If the power goes off during a write, the 
> index can contain invalid or incomplete data. A symptom of this can be that 
> the index only goes as far as B, so all the later records appear to be 
> missing when Access is using this index. However, if you sort differently, 
> so Access uses another index, all the records suddenly turn up again.
> 
> All databases uses indexes, and there is always a way to tell them to 
> rebuild their indexes. In Access, that's part of what the "repair" does 
> under:
>     Tools | Database Utilities | Compact/Repair
> 
> Sometimes it takes a bit more than that to fix the index, particularly where 
> other tables are connecting to this one based on that index. The article 
> explains how to handle those steps.
> 
> Of course, it is also possible that something else went wrong, e.g. the data 
> was actually deleted by someone, or a pointer to the actual data went bad, 
> or your disk sectors are cross linked. But the problem with the index is 
> more likely, so fingers crossed.
> 
> -- 
> Allen Browne - Microsoft MVP.  Perth, Western Australia
> Tips for Access users - http://allenbrowne.com/tips.html
> Reply to group, rather than allenbrowne at mvps dot org.
> 
> "Rocket Ron" <RocketRon@discussions.microsoft.com> wrote in message
> news:3F6E966C-CE79-4F42-A779-55F1937DE8D6@microsoft.com...
> > Thanks Allen
> > I always take a manual back-up copy and there is a mirrored external
> > hard-drive set-up. It's since this installation that I have found the 
> > problem.
> > I will study your suggestions and advise in due course, I have already
> > adjusted from the back-up so lucky so far. Must check what is meant by 
> > index.
> > Thanks again.
> >
> > "Allen Browne" wrote:
> >
> >> Ouch! You may have actually lost data, or you could be lucky. This can 
> >> occur
> >> when an index goes bad. If so, you may be able to rescue the data by
> >> deleting the index, and re-creating it.
> >>
> >> Details in the 2nd symptom in this article:
> >>     http://allenbrowne.com/ser-47.html#NumberOfRecordsVaries
> >>
> >> Be sure to make a copy of the database before doing anything else. This
> >> gives you multiple chances to try to rescue it.
> >>
> >> "Rocket Ron" <Rocket Ron@discussions.microsoft.com> wrote in message
> >> news:C7F04B1B-F836-4738-81FA-16E99DC8E479@microsoft.com...
> >> > When taking a regular back-up copy I noticed that the size of my 
> >> > database
> >> > had
> >> > halved, from 47MB to 23.5MB without any apparent loss of data.
> >> > I now see that one table is approximately 25% of its original size , 
> >> > where
> >> > the list of names now only reaches "B" instead of "Z" as before? 
> 
> 
0
Utf
9/8/2007 8:44:03 AM
"Rocket Ron" <RocketRon@discussions.microsoft.com> wrote in message
news:9B171BC1-505B-4B8F-8CE2-41D82A648653@microsoft.com...
> Regards, Ron (what does MVP stand for?)

MVP stands for Most Valuable Professional. It's an award Microsoft gives to 
people who share their expertise with users.

General info:
    https://mvp.support.microsoft.com/gp/mvpexecsum

Access MVPs:
    https://mvp.support.microsoft.com/communities/mvp.aspx?product=1&competency=Microsoft%20Office%20Access

-- 
Allen Browne - Microsoft MVP.  Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

0
Allen
9/8/2007 9:15:02 AM
Reply:

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