EZP-29194: Improve repo prefix handling for purgeAll() and user context hash tagging

[andrerom]

Issue: https://jira.ez.no/browse/EZP-29194

Followup to fix the following edge cases:

• Prefix tag for user context hash, so it can be correctly purged when repo prefixes er in use
• Always tag responses with unprefixed ez-all, as this is used in purgeAll() on Varnish and Fastly. Makes sure purgeAll() works the same in all Proxies; clearing all cache across all repositories.
  • Note: To clear all cache but only for a specific repo, use (purge(['ez-all'])) or from command line using fos command to clear by ez-all tag, these calls will/should be prefixed.

Follow up on this is to add a optional cache clearer for symfony that takes advantage of the fixes in purgeAll() to call that when user is calling bin/console cache:clear

[andrerom]

In ExceptionConversion.php line 104:
                  
  Database error  
                  
In AbstractMySQLDriver.php line 42:
                                                                               
  An exception occurred while executing 'SELECT `ezuser`.`contentobject_id`,   
  `ezuser`.`login`, `ezuser`.`email`, `ezuser`.`password_hash`, `ezuser`.`pas  
  sword_hash_type`, `ezuser_setting`.`is_enabled`, `ezuser_setting`.`max_logi  
  n` FROM `ezuser` LEFT JOIN `ezuser_setting` ON `ezuser_setting`.`user_id` =  
   `ezuser`.`contentobject_id` WHERE LOWER(`ezuser`.`login`) = :placeholder1'  
   with params ["admin"]:                                                      
                                                                               
  SQLSTATE[42S02]: Base table or view not found: 1146 Table 'ezp.ezuser' does  
  n't exist   

@adamwojs rings a bell? (this is against ezplatform:master)

Seems this is unrelated

[andrerom]

@vidarl Passing and ready for your review (behat failure is unrelated to PR)
Same goes for you QA.

[vidarl]

LGTM, but I have a few comments

So, prefix on default install will be "default_" ?
One worry I have with this prefix idea is that key size will increase and varnish and fastly have a limitation on header sizes

[andrerom]

So, prefix on default install will be "default_" ?

afaik default have a empty prefix

But yes, even when this is not set we have had cases where customers have reached the limit on Varnish. So @kmadejski added doc on how to extend the limit as it's configurable. Last followup on that here: https://github.com/ezsystems/developer-documentation/pull/491/files

Limit for Fastly seems to be 16Kb:
https://docs.fastly.com/guides/debugging/resource-limits#request-and-header-limits

So seems to be twice the default 8Kb limit of Varnish, but as it's not configurable that might be an issue in extreme cases.

We have talked about maybe cutting down on the tag sizes and phase out the current tags in favour of shorter variants. Afaik that is the only thing we can do, besides documenting that people should use short repo names (we can also log warnings about that here btw).