D8 Version and queue gardening

Current driver status

Maintained branches:

8.x-1.x: Passes install and is a 1-to-1 port (and kept in sync hopefully) with 7.x-2.x.

7.x-2.x: Many bugfixes, compatibility improvements, and the most important, uses client buffered queries.

For a list of changes/improvements, see:

#2479791: [meta] Changes in the 7.x-2.x driver version

This patch must be applied in order to get past install in using 7.x-2.x:

#2376239: "format" field in table "date_format_locale" should be case sensitive

It must be run along with the Wincache Module in order to leverage the performance boost:

https://www.drupal.org/project/wincachedrupal

About stability and compatiblity of the 7.x-2.x and 8.x-1.x branches: One of the key changes in these branches is the use of client buffered queries, but with that change a can of worms was opened:

• The change introduced a few bugs - that have been sorted out now - because buffered queries in the PDO driver are buggy.
• The change severly boosted the minimum required environment software to run the SQL Server driver and you now need:
  • ODBC 11
  • Wincache >= 1.3.7.4
  • PDO >= 3.2.0.0
  • PHP >= 5.5
  • Recommended SQL Server 2012 or above

  Was the introduction of client buffered queries necessary? I am not sure if the introduced bugs and the boosted requirement list was worth the change, but many users in the PHP world have reported masive performance gains when using client buffered queries in PDO drivers in general and the driver's code was simplified.

  Can we make client buffered queries an optional feature? The driver was completely refactored and it could be relatively easy to support switching buffered queries on/off based on a config setting.

Legacy branches

7.x-1.x: 7.x-1.3 and 7.x-dev should be quite stable, the latest dev for this branch solves the 2100 parameter limit issue + duplicate placeholder issue, that have been around for a while:

#1686872: MS-SQL query: 2100 parameters limit

Drupal 8 known issues

D8 has several core SQL Server compatibility issues, that affect basic functionality such as the creation,viewing and edition of nodes:

#1598924: Query with duplicate placeholders throws PDO Exception
#2342377: Non database agnostic expression in SQLContentEntityStorage
#2279395: The PostgreSQL backend does not handle NULL values for serial fields gracefully
#2342699: SqlContentEntityStorage tries to update identity/serial values by default