The query cache module did not check for the SQL_NO_CACHE keyword before
attempting to query the hash lookup table. This had a small performance impact.
By introducing a check on the query string before obtaining the hash mutex
we can gain some performance if the SQL_NO_CACHE directive is used often.
return no rows
The algorithm of determining the best key for loose index scan is doing a loop
over the available indexes and selects the one that has the best cost.
It retrieves the parameters of the current index into a set of variables.
If the cost of using the current index is lower than the best cost so far it
copies these variables into another set of variables that contain the
information for the best index so far.
After having checked all the indexes it uses these variables (outside of the
index loop) to create the table read plan object instance.
The was a single omission : the key_infix/key_infix_len variables were used
outside of the loop without being preserved in the loop for the best index
so far.
This causes these variables to get overwritten by the next index(es) checked.
Fixed by adding variables to hold the data for the current index, passing
the new variables to the function that assigns values to them and copying
the new variables into the existing ones when selecting a new current best
index.
To avoid further such problems moved the declarations of the variables used
to keep information about the current index inside the loop's compound
statement.
Started fix in 5.0 as the same issue is here.
Revising queries used given what appears to be the scope of this test to only select the manipulated variables.
Added tests for values that are / are not multiples of 1024 to test rounding / constraints.
This behavior is not currently documented (docs bug has been opened)
*with --with-charset=utf8*
Problem: wrong LONG TEXT field length is sent to a client
when multibyte server character set used.
Fix: always limit field length sent to a client to 2^32,
as we store it in 4 byte slot.
Note: mysql_client_test changed accordingly.
