during last upgrade:

(mysql): CREATE UNIQUE INDEX mdl_cachflag_flanam_uix ON mdl_cache_flags (flagtype, name) 1071: Specified key was too long; max key length is 1000 bytes

ADOConnection._Execute(CREATE UNIQUE INDEX mdl_cachflag_flanam_uix ON mdl_cache_flags (flagtype, name), false) % line 891, file: adodb.inc.php
ADOConnection.Execute(CREATE UNIQUE INDEX mdl_cachflag_flanam_uix ON mdl_cache_flags (flagtype, name)) % line 89, file: dmllib.php
execute_sql(CREATE UNIQUE INDEX mdl_cachflag_flanam_uix ON mdl_cache_flags (flagtype, name), true) % line 2091, file: dmllib.php
execute_sql_arr(Array[2], true, true) % line 665, file: ddllib.php
create_table(Object:XMLDBTable) % line 2283, file: upgrade.php