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recover deleted records

Hi

Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened

Louis
Nov 13 '05 #1
5 28984
Grant wrote:
Hi

Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened

Louis

www.pksolutions.com

Do not compact the database.

--
Error reading sig - A)bort R)etry I)nfluence with large hammer
Nov 13 '05 #2
"Grant" <ja*********@ho tmail.com> wrote:
Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened


Even Peter Miller, who recovers corrupted MDB files, states this can't be done. So
I'd look at retrieving those records from a backup.

Delete Records or Deleted Tables from Microsoft Access MDBs
http://www.granite.ab.ca/access/deletedata.htm

Tony
--
Tony Toews, Microsoft Access MVP
Please respond only in the newsgroups so that others can
read the entire thread of messages.
Microsoft Access Links, Hints, Tips & Accounting Systems at
http://www.granite.ab.ca/accsmstr.htm
Nov 13 '05 #3
Tony Toews wrote:
"Grant" <ja*********@ho tmail.com> wrote:

Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened

Even Peter Miller, who recovers corrupted MDB files, states this can't be done.


That surprised me.
So
I'd look at retrieving those records from a backup.


Let's hope the next question is not "what backup?"

--
Error reading sig - A)bort R)etry I)nfluence with large hammer
Nov 13 '05 #4
Trevor,
Tony Toews wrote:
"Grant" <ja*********@ho tmail.com> wrote:

Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened

Even Peter Miller, who recovers corrupted MDB files, states this can't be done.


That surprised me.


It's by design. Access overwrite a deleted record using the record at
the top of a data page. So all records a page are overwritten, not
only 'deleted'. Except for the one which has been at the top: this one
can be recovered. THIS IS THE NORMAL CASE, we name it the 'overwriting
technic'.

We have seen twice, that Access has'nt deleted the records in this
manner during a mass deletion (no deletion of the table itself, to be
clear, this would be easy to recover). So we could recover all records
of these two tables. But this behavior is very rarely. We have no idea
why Access has'nt used the overwriting technic.

We have found, that Access (tested with Access 2000) puts each NEW
record at a single page AFTER the table structure has been changed
until the database is compacted. I think, it's a bug of Access. As
long as it's possible to recover exactly one record per page, all
records can be recovered, which are stored in this manner.
So
I'd look at retrieving those records from a backup.


Let's hope the next question is not "what backup?"


Regards

Thilo Immel
Access Druid www.atroplan.com
Access Memory Reporter www.atroplan.com/AccMemReporter.htm

Nov 13 '05 #5

On Tue, 10 Aug 2004 08:37:02 +0100, Trevor Best wrote:
Tony Toews wrote:
"Grant" <ja*********@ho tmail.com> wrote:

Is there a way to recover deleted records from a table. A mass deletion has
occurred and Access has been closed since it happened

Even Peter Miller, who recovers corrupted MDB files, states this can't be done.


That surprised me.


I've posted on this before. Tony's overstating things to say that
I've said that deleted records can't be undeleted, but its only a very
slight overstatement. What I've said is that for all practical
purposes, deleted records (where the records, but not the table, have
been deleted) can't be undeleted in most cases. As Thilo points out
in this thread, the FIRST deleted record on a data page can be fully
undeleted, but all SUBSEQUENT deleted records on that page can NOT be
recovered because the first deleted record is copied over the
remaining records.

The average data page holds 20-30 records, although it could hold from
one to 200 or so records. The actual number depends on a variety of
factors (whether unicode is used, how many fields, what data types,
whether existing pages are full, etc) but the primary limiting factor
is the space required to store the average field. More specifically,
virtually all non-text fields require storage whether or not they are
used, all memo/ole/binary fields are stored outside of the data page,
and all text fields use storage only if they have values. There's
various places you can look for more specific information on storage
requirements, but this should give you an idea.

So, assuming Access can fit about 25 records per data page (which is
not at all unusual for a typical table), if your table has 100,000
records, it would take 4,000 data pages to store this data (in a fully
compacted database). If you delete all of these records and send your
file off to us (or some other company), the first record on each of
these pages could be recovered (so you get back 4,000 distinct
records). Another 96,000 records could, generally, be recovered, but
they would be 24 copies of each of the 4,000 distinct records. So, in
a case like this, there's no point in returning 100,000 records and
saying there's 100% recovery, because we know that 96% of these are
bogus copies. But at the same time, there's no reason to say no
recovery whatsoever is possible. It is not at all a problem to
recover 4% of the original data. Of course, 4% is pretty lame, and
virtually useless in almost (but not) all cases.

If the records had a large number of fields, they will take more space
to store, and so a higher recovery rate is expected. But even if you
only had two records per page, you're still looking at 50% data loss.

So, to summarize, Tony's pretty much correct that this type of data
loss is fatal, but its always important to be as accurate as possible
in describing exactly what sort of loss occurs. While in many
applications, 5% data loss may be fatal, in some cases, even 90%+ data
loss is still considered by the client to be a case where recovery of
the remai9ning data is still desirable (for example, in criminal
investigative/forensics cases).

HTH,

Peter Miller
PK Solutions
Nov 13 '05 #6

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