On Fri, Jun 16, 2017 at 11:06:39AM +0300, Konstantin Knizhnik wrote:
> Encryption is much easier to implement than compression, because it is not
> changing page size. So I do not see any "complexity and flexibility
> challenges" here.
> Just for reference I attached to this mail our own encryption patch. I do

I didn't see you using CPU AES instructions, which can improve
performance by 3-10x.  Is there a reason?

> Postgres buffer manager interface significantly simplifies integration of
> encryption and compression. There is actually single path through which data
> is fetched/stored to the disk.
> It is most obvious and natural solution to decompress/decrypt data when it
> is read from the disk to page pool and compress/encrypt it when it is
> written back. Taken in account that memory is cheap now and many databases
> can completely fit in memory, storing pages in the buffer cache in plain
> (decompressed/decrypted) format allows to minimize overhead of
> compression/encryption and its influence on performance. For read only
> queries working with cached data performance will be exactly the same as
> without encryption/compression.
> Write speed for encrypted pages will be certainly slightly worse, but still
> encryption speed is much higher than disk IO speed.

Good point.

> I do not think that pluggable storage API is right approach to integrate
> compression and especially encryption. It is better to plugin encryption
> between buffer manager and storage device,
> allowing to use  it with any storage implementation. Also it is not clear to
> me whether encryption of WAL can be provided using pluggable storage API.

Yes, you are completely correct.  I withdraw my suggestion of doing it
as plugin storage.

> The last discussed question is whether it is necessary to encrypt temporary
> data (BufFile). In our solution we encrypt only main fork of non-system
> relations and do no encrypt temporary relations. It may cause that some
> secrete data will be stored at this disk in non-encrypted format. But
> accessing this data is not trivial. You can not just copy/stole disk, open
> database and do "select * from SecreteTable": you will have to extract data
> from raw file yourself. So looks like it is better to allow user to make
> choice whether to encrypt temporary data or not.

If we go forward with in-db encryption, I think we are going to have to
have a discussion about what parts of PGDATA need to be encrypted,
i.e., I don't think pg_clog needs encryption.

  Bruce Momjian  <br...@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

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