Write a better documentation and sample settings file

Thanks for this hard work! You are my savior :)
I updated the module description by adding results of your tests, and I'll start investigating the DBTNG module potential incompatibilities as soon as we resolved your gzip issue.

Thanks again.

supplied database engine seems now fixed as of alpha4

the $conf['memcache_servers'] and $conf['memcache_bins'] config is still required on D7, to set which memcache servers cache what.
the $conf['cache_class_****'] only specifies which cache engine deals with which tables.

taken from README.txt in Memcache 7.x-1.x-dev:

Here is an example configuration that has two clusters, 'default' and
'cluster2'. Five memcached instances are divided up between the two
clusters. 'cache_filter' and 'cache_menu' bins goe to 'cluster2'. All other
bins go to 'default'.
include_once('./includes/cache.inc');
include_once('./sites/all/modules/memcache/memcache.inc');
$conf = array(
 'cache_default_class' = 'MemCacheDrupal',
 'memcache_servers' => array('localhost:11211' => 'default',
 'localhost:11212' => 'default',
 '123.45.67.890:11211' => 'default',
 '123.45.67.891:11211' => 'cluster2',
 '123.45.67.892:11211' => 'cluster2'),
 'memcache_bins' => array('cache' => 'default',
 'cache_filter' => 'cluster2',
 'cache_menu' => 'cluster2'),
);

When reading the code, it seems that if servers is omitted, memcache uses localhost:11211, which is the default. Bins is mandatory if you have one or more servers, but it seems that all will use 'default' if you don't specify it.

default version:

<?php
/**
* Cache settings: Cache Backport (cache_backport)
*
* Cache API backport from Drupal 7, running on file, db, apc, xcache or memcache engines.
*/
$module_cache_backport_enabled = FALSE; // change to TRUE to enable
$module_cache_backport_default = TRUE; // change to FALSE to detect subdomain
$module_cache_backport_inc = './sites/all/modules/cache_backport/cache.inc';
// Conditional loading
if ( $module_cache_backport_enabled == TRUE ) {
 // Set domain/subdomain
 if ( $module_cache_backport_default == TRUE ) {
 $module_cache_backport_domain = 'default';
 } else {
 $module_cache_backport_domain = $_SERVER['SERVER_NAME'];
 }
 // Define cache engines:
 $module_cache_backport_database = TRUE; // set TRUE to enable Database (DrupalDatabaseCache)
 $module_cache_backport_database_inc = './sites/all/modules/cache_backport/database.inc';
 $module_cache_backport_filecache = FALSE; // set TRUE to enable File Cache (DrupalFileCache)
 $module_cache_backport_filecache_inc = './sites/all/modules/filecache_d7/filecache.inc';
 $module_cache_backport_apc = FALSE; // set TRUE to enable APC (DrupalAPCCache)
 $module_cache_backport_apc_inc = './sites/all/modules/apc_d7/drupal_apc_cache.inc';
 $module_cache_backport_memcache = FALSE; // set TRUE to enable Memcache (MemCacheDrupal)
 $module_cache_backport_memcache_inc = './sites/all/modules/memcache_d7/memcache.inc';
 $module_cache_backport_memcache_db = FALSE; // do not use yet
 $module_cache_backport_memcache_db_inc = './sites/all/modules/memcache_d7/memcache.db.inc';
 $module_cache_backport_memcache_session = FALSE; // do not use yet
 $module_cache_backport_memcache_session_inc = './sites/all/modules/memcache_d7/memcache-session.inc';
 // Load Include files
 if ( file_exists($module_cache_backport_inc) ) $conf['cache_inc'] = $module_cache_backport_inc;
 if ( $module_cache_backport_database == TRUE ) if ( file_exists($module_cache_backport_database_inc) ) $conf['cache_backends'][] = $module_cache_backport_database_inc;
 if ( $module_cache_backport_filecache == TRUE ) if ( file_exists($module_cache_backport_filecache_inc) ) $conf['cache_backends'][] = $module_cache_backport_filecache_inc;
 if ( $module_cache_backport_apc == TRUE ) if ( file_exists($module_cache_backport_apc_inc) ) $conf['cache_backends'][] = $module_cache_backport_apc_inc;
 if ( $module_cache_backport_memcache == TRUE ) if ( file_exists($module_cache_backport_memcache_inc) ) $conf['cache_backends'][] = $module_cache_backport_memcache_inc;
 if ( $module_cache_backport_memcache_database == TRUE ) if ( file_exists($module_cache_backport_memcache_database_inc) ) $conf['cache_backends'][] = $module_cache_backport_memcache_database_inc;
 if ( $module_cache_backport_memcache_session == TRUE ) if ( file_exists($module_cache_backport_memcache_session_inc) ) $conf['session_inc'] = $module_cache_backport_memcache_session_inc;
 // Define cache bins (defaults):
 $conf['cache_default_class'] = 'DrupalDatabaseCache'; // default, any/any/any, select memcache, apc, file or db
 //$conf['cache_class_bootstrap'] = 'DrupalDatabaseCache'; // bootstrap, all/every/medium, select apc > db
 $conf['cache_class_block'] = 'DrupalDatabaseCache'; // block, any/often/small, select memcache > db > file
 $conf['cache_class_cache'] = 'DrupalDatabaseCache'; // general, all/every/medium/often, select apc > db
 $conf['cache_class_content'] = 'DrupalDatabaseCache'; // field, page/some/large, select file > memcache > db
 $conf['cache_class_filter'] = 'DrupalDatabaseCache'; // filtered, page/some/large, select file > memcache > db
 $conf['cache_class_form'] = 'DrupalDatabaseCache'; // block, edit/rare/medium, select file > memcache > db
 $conf['cache_class_menu'] = 'DrupalDatabaseCache'; // menu, any/often/large, select memcache > db > file
 $conf['cache_class_page'] = 'DrupalDatabaseCache'; // node, page/often/large, select memcache > file > db
 //$conf['cache_class_pathdst'] = 'DrupalDatabaseCache'; // path, any/some/medium, select memcache > db > file
 //$conf['cache_class_pathsrc'] = 'DrupalDatabaseCache'; // path, any/some/medium, select memcache > db > file
 //$conf['cache_class_uc_price'] = 'DrupalDatabaseCache'; // multiprice, any/often/medium, select memcache > db > file
 //$conf['cache_class_session'] = 'DrupalDatabaseCache'; // session, any/any/small, select memcache > db
 $conf['cache_class_update'] = 'DrupalDatabaseCache'; // system, system/rare/large, select file > db
 //$conf['cache_class_users'] = 'DrupalDatabaseCache'; // users, any/some/large, select memcache > file > db
 $conf['cache_class_views'] = 'DrupalDatabaseCache'; // views, any/some/large, select memcache > file > db
 $conf['cache_class_views_data'] = 'DrupalDatabaseCache'; // views data, any/often/small, select apc > db
 // Define File Cache settings
 $conf['filecache_fast_pagecache'] = FALSE; // set TRUE to enable fast page serving
 $conf['filecache_directory'] = './sites/' . $module_cache_backport_domain . '/files/filecache'; 
 // Define APC settings
 $conf['apc_show_debug'] = FALSE; // set TRUE to enable debug mode
 // Define Memcache settings
 /*$conf['memcache_options'] = array(
 Memcached::OPT_BINARY_PROTOCOL => FALSE, // set TRUE to enable binary protocol when using memcached >= 1.4
 Memcached::OPT_COMPRESSION => FALSE, // set FALSE to disable compression for improved performance
 Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT, // set consistent distribution
 Memcached::OPT_HASH => Memcached::HASH_CRC, // set CRC32 hash method
 Memcached::OPT_CONNECT_TIMEOUT => 1000, // connection timeout in milliseconds
 Memcached::OPT_SERVER_FAILURE_LIMIT => 5, // failure limit for server connection attempts
 );*/
 $conf['memcache_servers'] = array(
 '127.0.0.1:11211' => 'default',
 );
 $conf['memcache_bins'] = array(
 'cache' => 'default',
 'cache_block' => 'default',
 //'cache_bootstrap' => 'default',
 'cache_content' => 'default',
 'cache_filter' => 'default',
 'cache_form' => 'default',
 'cache_menu' => 'default',
 'cache_page' => 'default',
 //'cache_pathdst' => 'default',
 //'cache_pathsrc' => 'default',
 //'cache_uc_price' => 'default',
 'cache_update' => 'default',
 'cache_views' => 'default',
 'cache_views_data' => 'default',
 //'session' => 'default',
 //'users' => 'default',
 );
 // Define Drupal cache settings:
 /*
 $conf['page_cache_without_database'] = TRUE; // set TRUE to skip starting the database (first define 'cache_page' bin)
 $conf['page_cache_invoke_hooks'] = FALSE; // set FALSE to not use aggressive caching
 $conf['page_cache_maximum_age'] = $variables['page_cache_maximum_age'];
 $conf['cache_lifetime'] = $variables['cache_lifetime'];
 $conf['page_compression'] = $variables['page_compression'];
 */
}

optimized version:

<?php
/**
* Cache settings: Cache Backport (cache_backport)
*
* Cache API backport from Drupal 7, running on file, db, apc, xcache or memcache engines.
*/
$module_cache_backport_enabled = TRUE; // change to TRUE to enable
$module_cache_backport_default = TRUE; // change to FALSE to detect subdomain
$module_cache_backport_inc = './sites/all/modules/cache_backport/cache.inc';
// Conditional loading
if ( $module_cache_backport_enabled == TRUE ) {
 // Set domain/subdomain
 if ( $module_cache_backport_default == TRUE ) {
 $module_cache_backport_domain = 'default';
 } else {
 $module_cache_backport_domain = $_SERVER['SERVER_NAME'];
 }
 // Define cache engines:
 $module_cache_backport_database = TRUE; // set TRUE to enable Database (DrupalDatabaseCache)
 $module_cache_backport_database_inc = './sites/all/modules/cache_backport/database.inc';
 $module_cache_backport_filecache = TRUE; // set TRUE to enable File Cache (DrupalFileCache)
 $module_cache_backport_filecache_inc = './sites/all/modules/filecache_d7/filecache.inc';
 $module_cache_backport_apc = TRUE; // set TRUE to enable APC (DrupalAPCCache)
 $module_cache_backport_apc_inc = './sites/all/modules/apc_d7/drupal_apc_cache.inc';
 $module_cache_backport_memcache = TRUE; // set TRUE to enable Memcache (MemCacheDrupal)
 $module_cache_backport_memcache_inc = './sites/all/modules/memcache_d7/memcache.inc';
 $module_cache_backport_memcache_db = FALSE; // do not use yet
 $module_cache_backport_memcache_db_inc = './sites/all/modules/memcache_d7/memcache.db.inc';
 $module_cache_backport_memcache_session = FALSE; // do not use yet
 $module_cache_backport_memcache_session_inc = './sites/all/modules/memcache_d7/memcache-session.inc';
 // Load Include files
 if ( file_exists($module_cache_backport_inc) ) $conf['cache_inc'] = $module_cache_backport_inc;
 if ( $module_cache_backport_database == TRUE ) if ( file_exists($module_cache_backport_database_inc) ) $conf['cache_backends'][] = $module_cache_backport_database_inc;
 if ( $module_cache_backport_filecache == TRUE ) if ( file_exists($module_cache_backport_filecache_inc) ) $conf['cache_backends'][] = $module_cache_backport_filecache_inc;
 if ( $module_cache_backport_apc == TRUE ) if ( file_exists($module_cache_backport_apc_inc) ) $conf['cache_backends'][] = $module_cache_backport_apc_inc;
 if ( $module_cache_backport_memcache == TRUE ) if ( file_exists($module_cache_backport_memcache_inc) ) $conf['cache_backends'][] = $module_cache_backport_memcache_inc;
 if ( $module_cache_backport_memcache_database == TRUE ) if ( file_exists($module_cache_backport_memcache_database_inc) ) $conf['cache_backends'][] = $module_cache_backport_memcache_database_inc;
 if ( $module_cache_backport_memcache_session == TRUE ) if ( file_exists($module_cache_backport_memcache_session_inc) ) $conf['session_inc'] = $module_cache_backport_memcache_session_inc;
 // Define cache bins (optimized):
 $conf['cache_default_class'] = 'DrupalDatabaseCache'; // default, any/any/any, select memcache, apc, file or db
 //$conf['cache_class_bootstrap'] = 'DrupalAPCCache'; // bootstrap, all/every/medium, select apc > db
 $conf['cache_class_block'] = 'MemCacheDrupal'; // block, any/often/small, select memcache > db > file
 $conf['cache_class_cache'] = 'DrupalAPCCache'; // general, all/every/medium, select apc > db
 $conf['cache_class_content'] = 'DrupalFileCache'; // field, page/some/large, select file > memcache > db
 $conf['cache_class_filter'] = 'DrupalFileCache'; // filtered, page/some/large, select file > memcache > db
 $conf['cache_class_form'] = 'DrupalFileCache'; // block, edit/rare/medium, select file > memcache > db
 $conf['cache_class_menu'] = 'MemCacheDrupal'; // menu, any/often/large, select memcache > db > file
 $conf['cache_class_page'] = 'MemCacheDrupal'; // node, page/often/large, select memcache > file > db
 //$conf['cache_class_pathdst'] = 'MemCacheDrupal'; // path, any/some/medium, select memcache > db > file
 //$conf['cache_class_pathsrc'] = 'MemCacheDrupal'; // path, any/some/medium, select memcache > db > file
 //$conf['cache_class_uc_price'] = 'MemCacheDrupal'; // multiprice, any/often/medium, select memcache > db > file
 //$conf['cache_class_session'] = 'MemCacheDrupal'; // session, any/any/small, select memcache > db
 $conf['cache_class_update'] = 'DrupalFileCache'; // system, system/rare/large, select file > db
 //$conf['cache_class_users'] = 'MemCacheDrupal'; // users, any/some/large, select memcache > file > db
 $conf['cache_class_views'] = 'MemCacheDrupal'; // views, any/some/large, select memcache > file > db
 $conf['cache_class_views_data'] = 'DrupalAPCCache'; // views data, any/often/small, select apc > db
 // Define File Cache settings
 $conf['filecache_fast_pagecache'] = TRUE; // set TRUE to enable fast page serving
 $conf['filecache_directory'] = './sites/' . $module_cache_backport_domain . '/files/filecache'; 
 // Define APC settings
 $conf['apc_show_debug'] = FALSE; // set TRUE to enable debug mode
 // Define Memcache settings
 /*$conf['memcache_options'] = array(
 Memcached::OPT_BINARY_PROTOCOL => FALSE, // set TRUE to enable binary protocol when using memcached >= 1.4
 Memcached::OPT_COMPRESSION => FALSE, // set FALSE to disable compression for improved performance
 Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT, // set consistent distribution
 Memcached::OPT_HASH => Memcached::HASH_CRC, // set CRC32 hash method
 Memcached::OPT_CONNECT_TIMEOUT => 1000, // connection timeout in milliseconds
 Memcached::OPT_SERVER_FAILURE_LIMIT => 5, // failure limit for server connection attempts
 );*/
 $conf['memcache_servers'] = array(
 '127.0.0.1:11211' => 'default',
 );
 $conf['memcache_bins'] = array(
 'cache' => 'default',
 'cache_block' => 'default',
 //'cache_bootstrap' => 'default',
 'cache_content' => 'default',
 'cache_filter' => 'default',
 'cache_form' => 'default',
 'cache_menu' => 'default',
 'cache_page' => 'default',
 //'cache_pathdst' => 'default',
 //'cache_pathsrc' => 'default',
 //'cache_uc_price' => 'default',
 'cache_update' => 'default',
 'cache_views' => 'default',
 'cache_views_data' => 'default',
 //'session' => 'default',
 //'users' => 'default',
 );
 // Define Drupal cache settings:
 $conf['page_cache_without_database'] = TRUE; // set TRUE to skip starting the database (first define 'cache_page' bin)
 $conf['page_cache_invoke_hooks'] = FALSE; // set FALSE to not use aggressive caching
 $conf['page_cache_maximum_age'] = $variables['page_cache_maximum_age'];
 $conf['cache_lifetime'] = $variables['cache_lifetime'];
 $conf['page_compression'] = $variables['page_compression'];
}

Changing the issue title to fit the real task to do here.

I am closing this issue, since it is for a Drupal version that now is not supported.
Please re-open it if the issue is also relevant for other project branches that require a supported Drupal version.