Do I need memcache?

I haven't tried memcache yet, but have tried Advanced Cache - to use it you have to run the patch files on Drupal core. For me it caused significant performance gains for logged in users (I primarily tried out the forum and path caches... both of which are evidently broken now in the current version for some reason - I believe I tried it on Drupal 5.7 using the 1.6 version - maybe it's broken for 5.9 or the broken notes refer only to the dev version... I haven't tried the other patches carefully yet).

If I'm understanding the article/benchmarks you referred to, it looks like it is comparing Drupal's core caching versus memcache for anonymous users. Robert Douglass suggests the combination of both Advanced Cache and memcache for improving things for logged in users.

-- David
absolutecross.com

Hope this will give u clear idea about caching

1. Content Caching
cache_set($cid, $data, $table = 'cache', $expire = CACHE_PERMANENT, $headers = NULL);

cache_get($cid, $table = 'cache')
cache_set now automatically serializes arrays and objects passed to it before saving them to the cache table. When retrieving data from the cache, cache_get now automatically unserializes the data when necessary. Simple datatypes such as strings and integers do not need to and will not be serialized before being stored

2. Block Caching
$blocks[0]['cache'] = BLOCK_CACHE_PER_PAGE | BLOCK_CACHE_PER_ROLE(default);
Drupal 6 now has a block-level cache, which improves performance for both authenticated and anonymous users. Site administrators can turn on block caching on the 'Performance' settings page(admin/settings/performance).

3. Menu Caching
menu_cache_clear($menu_name = 'navigation')

cache_clear_all($cid = NULL, $table = NULL, $wildcard = FALSE)
By default each menu item clicked is cached. For clearing particular menu item clicked we can use
cache_clear_all.
menu_cache_clear clears all menu cached.

4. Form Caching
form_set_cache($form_build_id, $form, $form_state)

form_get_cache($form_build_id, &$form_state)
In Drupal 6 the whole form can be stored in database using form cache. $form_build is our unique name for form to be cached.
$form is an array where it contains all form structure like textfield, checkboxes etc.
$form_state is an array which contains submitted or storaged.

5. Page Caching
Recommended Page Caching is Normal. Minimum cache life time can be set to clear page caching.
Site administrators can turn on page caching to “Normal” on the 'Performance' settings page(admin/settings/performance). For anonymous users page gets cached as blob/image in cache_page table.

6. Memory Caching (Memcache)
$memcache->set($key,$object,MEMCACHE_COMPRESSED,$timeout)

$memcache->get($key)
memcache used to speed up dynamic database-driven websites by caching data and objects in memory to reduce the number of times the database must be read. So instead of requesting lot of queries when a page is load, memcache stores result set of queries in server. And it fetches results from that instead of running queries. It his highly used for linux servers

6. Mysql Query Caching
set global query_cache_size=50000000;

Mysql query cache stores the SELECT queries issued by clients to the MySQL database server. In this respect, it acts a lot like traditional database SQL caches, in that identically issued queries will be located and re-issued by the database engine without hard parse activity. However, unlike any other database system, MySQL stores not only the SQL query issued by a client, but also stores the query's result set

7. Turck MMCache

Only Installation is required.
Turck MMCache is a opcode cache for PHP. It increases performance of PHP scripts by caching them in a compiled state, so that the overhead of compiling is almost completely eliminated. It also uses some optimizations for speeding up PHP scripts' execution. It typically reduces server load and increases the speed of PHP code by 1-10 times.
Other Caching Methods : APC , XCACHE, eAccelerator (Not Recommended to use for drupal)

But for better performance on Drupal: Turck MMCache is used rather than APC , XCACHE, eAccelerator. Similarly modules for those three were not developed on drupal. fastpath_fscache is for file caching, but there is no module developed for drupal 6.

Thanks
Devaraj
Analyst Programmer
Netlink Technologies.