query cache, only invalidate when table change

hi guys... well again query cache...

check this...

create table ae(b enum('a','b','c') not null);

insert into ae values ('a'),('b'),('c');

select * from information_schema.QUERY_CACHE_QUERIES; /* no query, nice */

select * from ae;

select * from information_schema.QUERY_CACHE_QUERIES; /* one query, nice too */

update ae set b='d' where b='d'; /* no row changed */

select * from information_schema.QUERY_CACHE_QUERIES; /* no queries ?! */

i didn't checked how each engine remove queries from query cache, but... should it only remove queries from query cache, if one+ row(s) change? this reduce table invalidation, increase query cache hit

idea of this MDEV: create a 'delayed' query cache invalidation, in other words, instead of invalidating when one UPDATE/DELETE/INSERT occur, only invalidate if one row changed, ok this is a problem with transactions where we don't know if it should or not be invalidated outside transaction, but, if update/delete don't change anything, why should it invalidate query cache?

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idea: instead of invalidating... first mark table to 'not allow new queries at query cache', after update/insert/delete, if row changed/affected>0 execute the invalidation, if <=0 'unlock' the table from query cache (allow new queries use this table), we will have some queries not cached cause we 'locked' insert into query cache using update/delete/insert table , but this increase query cache hit, and allow a lower resource consume invalidating always queries without rows changed