set session transaction_prealloc_size=1024*1024*1024*1;
show processlist;
Id	User	Host	db	Command	Time	State	Info
1	root	localhost	test	Query	0	NULL	show processlist
set session transaction_prealloc_size=1024*1024*1024*2;
show processlist;
Id	User	Host	db	Command	Time	State	Info
1	root	localhost	test	Query	0	NULL	show processlist
set session transaction_prealloc_size=1024*1024*1024*3;
show processlist;
Id	User	Host	db	Command	Time	State	Info
1	root	localhost	test	Query	0	NULL	show processlist
set session transaction_prealloc_size=1024*1024*1024*4;
show processlist;
Id	User	Host	db	Command	Time	State	Info
1	root	localhost	test	Query	0	NULL	show processlist
set session transaction_prealloc_size=1024*1024*1024*5;
show processlist;
Id	User	Host	db	Command	Time	State	Info
1	root	localhost	test	Query	0	NULL	show processlist
