Commits on Jan 25, 2024

1. Fix crashing innodb due to innobase_share usage_count not being reduc… …

   …ed for temp table accesses
   
   The MySQL engine is designed with the assumption that accesses to
   temporary tables will only ever occur from the thread that created
   the temporary table. Cross thread accesses of temporary tables are
   not expected and are therefore not designed for. However, if the
   information schema is queried for details about a temporary table,
   then the temporary table gets accessed from a thread that is
   different from the thread that created the temporary table,
   breaking the design assumption.
   
   When this cross-thread accesss of a temporary table happens for
   engines that use the InnoDB storage engine, the INNOBASE_SHARE
   use_count for the table gets incremented, but never gets
   decremented when the none-owning thread completes. In certain
   situations, this can lead to a crash of the database engine, when
   invariants in the function innobase_build_index_translation fail
   on assertion. For example we found a use case that cause MySQL
   to crash with the assertion failure below:
   
       (gdb) bt
       #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
       percona#1  0x00007f3132141859 in __GI_abort () at abort.c:79
       percona#2  0x000055ed7452a19a in ut_dbg_assertion_failed (expr=0x55ed7489f848 "share->idx_trans_tbl.index_count == mysql_num_index",
           file=0x55ed7489ea90 "/github/MySQL5.7/mysql-server/storage/innobase/handler/ha_innodb.cc", line=5680)
           at /github/MySQL5.7/mysql-server/storage/innobase/ut/ut0dbg.cc:75
       percona#3  0x000055ed7437ecda in innobase_build_index_translation (table=0x7f30bcaaa4d0, ib_table=0x7f30bc023888, share=0x7f30b002c100)
           at /github/MySQL5.7/mysql-server/storage/innobase/handler/ha_innodb.cc:5680
       percona#4  0x000055ed7437fe6d in ha_innobase::open (this=0x7f30bcaa6a10, name=0x7f30bcaab1c0 "./test/#sql-bae1d_3", mode=2, test_if_locked=2)
           at /github/MySQL5.7/mysql-server/storage/innobase/handler/ha_innodb.cc:6115
   
   The above issue is fixed by allowing the use_count for an
   INNODB_SHARE object of a temporary table to be decremented during
   query cleanup, whenever a temporary table is accessed from a
   none-owning thread. Care is taken to make sure that the use_count
   decrement is done inside of the a critical region protected by
   the innobase_share_mutex mutex.
   
   All new code of the whole pull request, including one or several files
   that are either new files or modified ones, are contributed under the
   BSD-new license. I am contributing on behalf of my employer Amazon Web
   Services, Inc.

   

   lottaquestions committed Jan 25, 2024
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