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Re: dump, drop database then merge/aggregate

On 29/02/16 16:32, Steven Siebert wrote:
What level of control do you have on the remote end that is
collecting/dumping the data?  Can you specify the command/arguments on how
to dump?  Is it possible to turn on binary logging and manually ship the
logs rather than shipping the dump, effectively manually doing replication?
in an overview it's a simple php app, a form of a questionnaire that collects user manual input, db backend is similarly simple, just one table. Yes I can operate mysqldump command but nothing else, I do not have control over mysql config nor processes.

It's one of those cases when for now it's too late and you are only thinking - ough... that remote box, if compromised would be good to have only a minimal set of data on it.

So I can mysqldump any way it'd be best and I'd have to insert ideally not replacing anything, instead aggregating, adding data. I think developers took care of uniqueness of the rows, and constructed it in conformity with good design practices.

What I'm only guessing is when I lock, dump and remove then insert, aggregate could there be problems with keys? And no data loss during dump+removal?

thanks for sharing your thoughts.

I agree with others, in general this approach smells like a bad idea.
However, updating data from a remote system in batch is quite common,
except often it's done at the application level polling things like web
services and perhaps some business logic to ensure integrity is
maintained.  Attempting to do it within the constructs of the database
itself is understandable, but there are risks when not adding that "layer"
of logic to ensure state is exactly as you expect it during a merge.

At risk of giving you too much rope to hang yourself: if you use mysqldump
to dump the database, if you use the --replace flag you'll convert all
INSERT statements to REPLACE, which when you merge will update or insert
the record, effectively "merging" the data.  This may be one approach you
want to look at, but may not be appropriate depending on your specific


On Mon, Feb 29, 2016 at 11:12 AM, lejeczek <peljasz@xxxxxxxxxxx> wrote:

On 29/02/16 15:42, Gary Smith wrote:

On 29/02/2016 15:30, lejeczek wrote:

On 28/02/16 20:50, lejeczek wrote:

fellow users, hopefully you experts too, could help...

...me to understand how, and what should be the best practice to dump
database, then drop it and merge the dumps..
What I'd like to do is something probably many have done and I wonder
how it's done best.
A box will be dumping a database (maybe? tables if it's better) then
dropping (purging the data) it and on a different system that dump swill be
inserted/aggregated into the same database.
It reminds me a kind of incremental backup except for the fact that
source data will be dropped/purged on regular basis, but before a drop, a
dump which later will be used to sort of reconstruct that same database.

How do you recommend to do it? I'm guessing trickiest bit might this
reconstruction part, how to merge dumps safely, naturally while maintaining
consistency & integrity?
Actual syntax, as usually any code examples are, would be best.

many thanks.

I guess dropping a tables is not really what I should even consider -
should I just be deleting everything from tables in order to remove data?
And if I was to use dumps of such a database (where data was first
cleansed then some data was collected) to merge data again would it work
and merge that newly collected data with what's already in the database

This sounds like a remarkably reliable way to ensure no data integrity.
What exactly are you trying to achieve? Would replication be the magic word
you're after?

I realize this all might look rather like a bird fiddling with a worm
instead of lion going for quick kill. I replicate wherever I need and can,
here a have very little control over one end.
On that end with little control there is one simple database, which data
I'll need to be removed on regular basis, before removing I'll be dumping
and I need to use those dumps to add, merge, aggregate data to a database
on the other end, like:
today both databases are mirrored/identical
tonight awkward end will dump then remove all the data, then collect some
and again, dump then remove
and these dumps should reconstruct the database on the other box.

Pointers on what to pay the attention to, how to test for consistency &
integrity, would be of great help.


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