database copying and compacting

[Pavel Kankovsky]

On Sun, 7 Nov 2004, David Relson wrote:

> Now, with 0.93.0 it's necessary to save log files and use dd (with
> proper block size) when copying the database.  Thus copying becomes:
> 
>    SIZE=`db_stat -h $ORIG -d wordlist.db | grep "page size" | cut -f 1` 
>    cp $SRC/log* $SRC/__db.* $DST  
>    for FILE in $SRC/*.db ; do
>        dd bs=$SIZE if=$FILE of=$DST/`basename $FILE`
>    done

According to Berkeley DB's "Database and log file archival"
(http://www.sleepycat.com/docs/ref/transapp/archival.html)
hot database backup (*) should copy db files BEFORE log files and the 
order is important. The requirement makes sense to me: if you copy log 
files first and db files next, you might end with db files containing 
data from updates missing in log files and the result will be 
unrecoverable. On the other hand, if you copy db files first and log 
files next, all data in db files can be either commited or rolled back 
using the information in log files (at least unless you drop some log 
files in the middle of backup).

Moreover, it might be a good idea to add something like
db_recover -c -h $DST in order to put the destination db into a 
consistent state.

(*) I assume this is what you intend to do because dd is necessary to 
guarantee page-level read consistency wrt concurrent writes.

--Pavel Kankovsky aka Peak  [ Boycott Microsoft--http://www.vcnet.com/bms ]
"Resistance is futile. Open your source code and prepare for assimilation."