Changes have been made in Git (master):

commit 9198c3c8fac5e8b4213a3e5853281ce2439a5c08
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Thu Feb 2 12:11:17 2017 -0500

     Allow Horde_Vfs::writeData to accept a stream as input.

     For every driver except Mongo, the stream is maintained. Mongo
     must read it into a string since there is no way to stream the
     bytes to the backend.

     Related to Bug: 10775.

  framework/Vfs/lib/Horde/Vfs/Base.php    | 31 ++++++++++++++++++++++++++-----
  framework/Vfs/lib/Horde/Vfs/File.php    | 15 ++++++++++-----
  framework/Vfs/lib/Horde/Vfs/Ftp.php     | 12 ++++++++----
  framework/Vfs/lib/Horde/Vfs/Mongo.php   |  7 +++++++
  framework/Vfs/lib/Horde/Vfs/Musql.php   |  9 +++++----
  framework/Vfs/lib/Horde/Vfs/Smb.php     | 12 ++++++++----
  framework/Vfs/lib/Horde/Vfs/Sql.php     |  9 +++++----
  framework/Vfs/lib/Horde/Vfs/SqlFile.php |  3 +++
  framework/Vfs/lib/Horde/Vfs/Ssh2.php    | 12 ++++++++----
  framework/Vfs/package.xml               |  2 +-
  10 files changed, 81 insertions(+), 31 deletions(-)

http://github.com/horde/horde/commit/9198c3c8fac5e8b4213a3e5853281ce2439a5c08

Why don't we add stream support for blobs to Horde_Db? Is there an 
open enhancement for that?

Sure enough... moving to a file based VFS backend, memory usage was 
4-5 times less.  Simply put, Horde_Db is terribly inefficient.

Since that has nothing to do with VFS itself, closing this ticket.   
Horde_Db would benefit from log fixes in Ticket #10773, so that's a 
start.  Better would probably be informing users that they should NOT 
be using SQL VFS in production environments.

A quick pass at this is not promising, at least for the SQL driver: 
the critical issue seems to instead be that Horde_Db does not accept 
stream resources as input - it expects everything in strings.  Which 
is depressing - this is going to make tuning very difficult, and 
pretty much makes Horde_Db the bottleneck when it comes to memory 
usage improvements.

So... for all the advances we have made in memory reduction in Horde 
4, VFS kills much of the joy.  Uploading a 1.2 MB attachment to IMP, a 
call to VFS::write(), using a Postgresql DB backend, uses 35.5 MB of 
memory.  That is unacceptable.

This ticket is partially related to Ticket #10773 - eliminating 
logging within the DB object reduces memory usage to 15 MB.  Still too 
high, but not as bad.