I discovered a problem in DBMirror.pl, performance wise.
pending.c stores data in a way
very similar to the PgSQL input "\" escaped format.
When the field is of type bytea, and the source of data is binary, then
this produces 2 additional backslashes for every unprintable
char.
The performance in function extractData in DBMirror.pl, really suffers
from this condition, since it breaks data in chunks of "\" delimited
strings.
Informally speaking, performance tends to be O(n) where n is the size
of the data.
This can be remedied if we break data in chunks of "'" rather than "\".
"'" happens much more infrequently in common binary files (bz2, tiff, jpg,
pdf etc..), and if we notice that odd number of contained "\", signals an
intermidiate "'", whereas even number of "\" signals the final "'",
then we can make this routine run much faster.
I attach the new extractData function.
Now replicating a 400 k tiff takes 3 seconds instead of 12 minutes
it used to do.
I am wondering about the state of
http://www.whitebeam.org/library/guide/TechNotes/replicate.rhtm
Please feel free for any comments.
Pete could you test this new DBMirror.pl, to see how it behaves
in comparison with your C++ solution?
--
-Achilleus
