PS-5562 : index_merge + partitioning + MyRocks crashes the server

[satya-bodapati]

Problem:

With native paritioning and index_merge, the native partition handler
is cloned.

One important point missed when fixing PS-5206 is that both the original
and clone share the parition_info object (m_part_info). It has bitmap of
partitions read and used.

The cloned handler, which has reference to the shared to partition_info
object, resets the partition bitmap during creation. This causes problem
during the actual index scan.

Fix:

1. Create context to identify if the native partition handler creation is
   from clone or brand new.

2. When it is clone, do not reset the partition bitmaps (i.e avoid calling
   m_part_info->set_partition_bitmaps()). This is the core fix.

3. Additionally, we fix the cloned object creation to use clone mem_root
   instead of TABLE*->mem_root. Optimizer can destroy the cloned handler
   immediately after its use. (See QUICK_RANGE_SELECT::~QUICK_RANGE_SELECT).

[satya-bodapati]

8.0 version will have testcase because the optimizer hint to force /*+ INDEX_MERGE */ is introduced only in 8.0. This is not present in 5.7.

To reproduce the crash, we need native partitioning + index_merge + only a subset of partitions should be used for query. Tried for two days before giving up.

8.0 version has simple testcase.

[satya-bodapati]

./mtr --mem --suite=tokudb.parts --parallel=4 --force --retry-failure=0|tee mtr.log
 93%] tokudb.parts.upgrade_from_prev_ver 'native-partitioning' w4 [ pass ]  13338
[ 94%] tokudb.parts.partition_float_tokudb 'native-partitioning' w4 [ pass ]   1185
[ 95%] tokudb.parts.partition_syntax_tokudb 'native-partitioning' w4 [ pass ]    165
[ 96%] tokudb.parts.partition_value_tokudb 'native-partitioning' w4 [ skipped ]  # CAST() in partitioning function is currently not supported.
[ 97%] tokudb.parts.partition_exchange_tokudb 'non-native-partitioning' w1 [ pass ]  40126
[ 98%] tokudb.parts.partition_exchange_tokudb 'native-partitioning' w2 [ pass ]  40175
[100%] tokudb.parts.partition_special_tokudb 'native-partitioning' w3 [ pass ]  27387
--------------------------------------------------------------------------
The servers were restarted 12 times
Spent 181.175 of 80 seconds executing testcases

Completed: All 55 tests were successful.

36 tests were skipped, 25 by the test itself.


===============================
./mtr --mem --suite=rocksdb --parallel=4 --force --retry-failure=0|tee mtr.log


[100%] rocksdb.autoinc_crash_safe_partition 'write_committed' w2 [ pass ]  80331
--------------------------------------------------------------------------
The servers were restarted 119 times
Spent 3606.150 of 1161 seconds executing testcases

Completed: Failed 5/495 tests, 98.99% were successful.

mysql-test-run: *** ERROR: there were failing test cases
Failing test(s): rocksdb.multi_con_read rocksdb.persistent_cache

[satya-bodapati]

multi_con_read is result content mismatch. I hve recorded this as part of this commit.