dflt_key_cache->key_cache_mem_size is not set, signal hanlder prints key_buffer_size=0 in the error log

[Elena Stepanova]

When server gets a signal which causes an abort and attempts to print some debug info in the error log, key_buffer_size is displayed equal 0. It seems to be always so in MariaDB 5.2, 5.3, 5.5, while in MariaDB 5.1, MySQL 5.1 and 5.5 the real value is printed.

From what I could see from a quick look, the printed value is dflt_key_cache->key_cache_mem_size, and in MariaDB 5.2 it does not seem to be set, although used, while in MariaDB 5.1 it is set on startup.

I'm not sure how much the variable is used later, so it might be only a cosmetic problem (bad error message), or a functional issue if some other code relies on the value.

To reproduce the visible effect, start mysqld, let it start up properly, then kill it with SIGABRT or alike and see the error output:

We will try our best to scrape up some info that will hopefully help diagnose the problem, but since we have already crashed, something is definitely wrong and this may fail.

key_buffer_size=0
read_buffer_size=131072
max_used_connections=0
max_threads=153
threads_connected=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 334074 K bytes of memory