Re: WAL directory size calculation

[Moreno Andreo <moreno.andreo@xxxxxxxxxx>]

Il 29/07/2016 15:13, FarjadFarid(ChkNet) ha scritto:

 

If you add a URL to an ftp with SSL certificate. Your backup will be much quicker and if someone stole the computer the images are still encrypted as before. It is just the source where data comes from that changes. 

... and if while working the Internet connection drops....? or my office is not covered by broadband at all (and, still in 2016, in Italy there are so many places not covered by broadband... no adsl, no wi-max, low-performing mobile)?
Local copies of databases that we synchronize are made to permit users to work even if no internet connection is available (since they're doctors, they have to have their data available almost all the time)

This architecture is made by design. Some years ago, when we started designing our software, we went into this situation, and the question was "Why don't we have just a remote server and users connect remotely, instead of having replicas in their places?"
This can ease updates, troubleshooting, almost everything.
After a while, the answer we went into is exactly as above. Until we have slow and unreliable Internet connections (fiber coverage is growing, but it's still very sparse) so we can't count on them, we can't rely only to a remote server.

Thanks
Moreno

 

 

From: Moreno Andreo [mailto:moreno.andreo@xxxxxxxxxx]
Sent: 29 July 2016 12:08
To: FarjadFarid(ChkNet) <farjad.farid@xxxxxxxxxxxxxxxxx>; pgsql-general@xxxxxxxxxxxxxx
Subject: Re: WAL directory size calculation

 

Il 29/07/2016 11:44, FarjadFarid(ChkNet) ha scritto:

 

The question to ask is what benefit would you gain by saving BLOB object on a database than on say a flat file server or url on an ftp server? Specially larger ones.

Privacy. Blobs are stored encrypted, since they are health-related images or documents.
You should be right if all of this data would be resident only on our server (that can only be accessed by application), but every user has a small PG cluster in his PC with his patients data and images that replicates continuously with our server.
Our application runs on Windows. To get into patient data from another user (say, someone that stole the computer) is a bit tricky, because you have to know how to exclude authentication in postgres and even after this, you have to know where to search and what to search and sometines what is the meaning on the encodings.
Imagine if we have a folder containing all images.... double click and open...

Another point is a bit of self-defense. Our users are far to be smart computer users, and in the past we had some cases in which someone, trying to clean up a filled-up disk, deleted a directory under his Paradox database (!!!) and then asked us why the app was not loading anymore....
 

BLOB’s cause a lot problem for all DBs. Not unless the DB engine can understand their structure and process them. It is not worth the effort.

It can hit the DB performance in Indexing, backups, migrations and load balancing.

Regarding backups I disagree. Files related to database must be consistent to the database itself, so backup must be done saving both database and images. AFAIK there's not a big difference in backing up image files versus BLOBS in a database.
I agree about load balancing, but only in case of a bulk load of several megabytes. (our actual server got an overload 2 months ago when a client we were activating sent a transaction with the insertion of 50 blobs sizing about 300 megabytes)

 

 

Hope this helps.

 

 

 

From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general-owner@xxxxxxxxxxxxxx] On Behalf Of Moreno Andreo
Sent: 29 July 2016 10:19
To: pgsql-general@xxxxxxxxxxxxxx
Subject: Re: WAL directory size calculation

 

Il 29/07/2016 10:43, John R Pierce ha scritto:

 

Aside of this, I'm having 350 DBs that sum up a bit more than 1 TB, and plan
to use wal_level=archive because I plan to have a backup server with barman.

 

With that many databases with that so many objects

350 DBs with about 130 tables and a bunch of sequences each, for the sake of precision.
With extensive use of BLOBs.

and undoubtable client connections,

Yes, that's another big problem... we run normally between 500 and 700 concurrent connections... I had to set max_connections=1000, the whole thing grew up faster than we were prepared for...

I'd want to spread that across a cluster of smaller servers.

That will be step 2... while migration is running (and will run for some months, we have to plan migration with users) I'll test putting another one or two machines in cluster, make some test cases, and when ready, databases will be migrated on other machines, too.
I posted a question about this some months ago, and I was told that one solution would be to set the servers to be master on some databases and slave on others, so we can have a better load balancing (instead of having all writes on the sole master, we split among all masters depending on which database is getting the write command, especially when having to write BLOBs that can be some megabytes in size).
I don't know to achieve this, but I will find a way somewhere.

just sayin...

ideas are always precious and welcome.

 

-- 

john r pierce, recycling bits in santa cruz