The last 48 hours or so I spend on trying to determine the cause for sporadic crashes of my MySQL (Aurora) DB. Turns out they were attributed to my mixing of database, table, column and stored procedure collation/charsets. My bad, or is it?
Aurora aside, what were the practical reasons for all the ways to configure charset/collation in MySQL? Why couldn't utf8 just become utf8mb4 as part of a major release? Why changing charset or collation of a database/table doesn't actually change the database or table, only future additions to the schema? The last one provides for an opportunity to have a mix of columns charset/collations in your tables, for instance. What sane person would want to have different charsets/collations within the same DB? And if there is a rationale for all this madness, why not make it the exception rather than the norm when configuring mysqld?
In my case, to resolve mysqld crashes I had to ensure all of below return consistent charset/collation values:
show procedure status where db = '<database>'; SELECT default_character_set_name FROM information_schema.SCHEMATA WHERE schema_name = "<database>"; SELECT T.table_name, CCSA.character_set_name FROM information_schema.`TABLES` T, information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA WHERE CCSA.collation_name = T.table_collation AND T.table_schema = "<database>" ; SELECT table_name, column_name, character_set_name FROM information_schema.`COLUMNS` WHERE table_schema = "<database>";
Example crash stack trace which appears to be tied to my mixing of charset/collation types:
mysqld got signal 11 ; This could be because you hit a bug. It is also possible that this binary or one of the libraries it was linked against is corrupt, improperly built, or misconfigured. This error can also be caused by malfunctioning hardware. 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=16777216 read_buffer_size=262144 max_used_connections=22 max_threads=2000 thread_count=18 connection_count=18 It is possible that mysqld could use up to key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 1070055 K bytes of memory Hope that's ok; if not, decrease some variables in the equation. Thread pointer: 0x2a2a2a50d000 Attempting backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong... stack_bottom = 0x2a2a2a50d000 thread_stack 0x40000 /rdsdbbin/oscar/bin/mysqld(my_print_stacktrace+0x2c)[0x960ccc] /rdsdbbin/oscar/bin/mysqld(handle_fatal_signal+0x491)[0x6d7bb1] /lib64/libpthread.so.0(+0xf5b0)[0x2b299b88d5b0] /rdsdbbin/oscar/bin/mysqld(_ZN4JOIN7prepareEP10TABLE_LISTjP4ItemjP8st_orderS5_S3_P13st_select_lexP18st_select_lex_unit+0x127d)[0x76e0fd] /rdsdbbin/oscar/bin/mysqld(_Z12mysql_selectP3THDP10TABLE_LISTjR4ListI4ItemEPS4_P10SQL_I_ListI8st_orderESB_S7_yP13select_resultP18st_select_lex_unitP13st_select_lex+0x86b)[0x776eab] /rdsdbbin/oscar/bin/mysqld(_Z13handle_selectP3THDP13select_resultm+0x127)[0x777067] /rdsdbbin/oscar/bin/mysqld[0x5ac17d] /rdsdbbin/oscar/bin/mysqld(_Z30mysql_execute_command_internalP3THD+0x3c74)[0x7556d4] /rdsdbbin/oscar/bin/mysqld(_Z21mysql_execute_commandP3THD+0x30)[0x757670] /rdsdbbin/oscar/bin/mysqld(_ZN18Prepared_statement7executeEP6Stringb+0x354)[0x768914] /rdsdbbin/oscar/bin/mysqld(_ZN18Prepared_statement12execute_loopEP6StringbPhS2_+0xb6)[0x768ad6] /rdsdbbin/oscar/bin/mysqld(_Z19mysqld_stmt_executeP3THDPcj+0x153)[0x768d73] /rdsdbbin/oscar/bin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0x12e4)[0x75a204] /rdsdbbin/oscar/bin/mysqld(_ZN22OscarSchedulerConsumer7consumeEjj+0xc0)[0x7e5610] /rdsdbbin/oscar/bin/mysqld(_ZN22OscarSchedulerConsumer5startEv+0xa0)[0x7e5720] /rdsdbbin/oscar/bin/mysqld(_ZN22OscarSchedulerConsumer11drain_queueEPv+0x6a)[0x7e596a] /lib64/libpthread.so.0(+0x7f18)[0x2b299b885f18] /lib64/libc.so.6(clone+0x6d)[0x2b299e658b2d]