In-Memory的Join Group 的数据字典位于内存的何处？
有客户问到，使用Oracle 的In-Memory功能时，如果用到了 Join Group，
那么这些这些Join Group，位于内存的何处？
根据同事的执行结果，整理如下：
1.prepare test env.
create table t1 as select * from dba_tables
create table t2 as select * from dba_tables
create inmemory join group t_join (t2(table_name),t1(table_name) )
create inmemory join group t_join1 (t2(owner),t1(owner) )
alter table t1 inmemory
alter table t2 inmemory
alter system set inmemory_size =300M
==run sql
SELECT t1.owner,t2.table_name
FROM t1 , t2
WHERE t1.table_name = t2.table_name
==check gd
SELECT o.object_name Table_Name, c.column_name Column_Name, gd.head_address AS "GD Address"
FROM user_objects o, user_tab_columns c, v$im_segdict gd
WHERE gd.objn = o.object_id
AND o.object_name = c.table_name
AND gd.column_number = c.column_id;
T1 TABLE_NAME 000000008A8B10F0
T2 OWNER 000000008A8310F0
对内存进行Dump：
==dum sga memory
HEAP DUMP heap name="IMCA_RW" desc=0x60001178 ***<<<<<heap name , following chunks belong this heap.
extent sz=0x1040 alt=336 het=32767 rec=0 flg=0x2 opc=0
parent=(nil) owner=(nil) nex=(nil) xsz=0x3bfffd0 heap=(nil)
fl2=0xa4, nex=(nil), idx=0, dsxvers=1, dsxflg=0x0
dsx first ext=0x89800030
dsx empty ext bytes=0 subheap rc link=0x898000a0,0x898000a0
pdb id=1, src pdb id=1
EXTENT 0 addr=0x89800030
Chunk 089800040 sz= 112 perm "perm " alo=112
Dump of memory from 0x0000000089800040 to 0x00000000898000B0
.............
Chunk 08a7e10d8 sz= 46137368 freeable "cimadrv "
Dump of memory from 0x000000008A7E10D8 to 0x000000008D3E10F0 ***<<<<<this chunk cover these two address.
Repeat 3489 times
08A8B10F0 0A0A0A0A 00011E8E 00000001 00000836 [............6...]
08A8B1100 8A8C10F0 00000000 00000000 00000000 [................]
08A8B1110 00000000 00000000 00000000 00000000 [................]
Repeat 3489 times
08A8310F0 0A0A0A0A 00011E8F 00000000 00000014 [................]
08A831100 8A8410F0 00000000 00000000 00000000 [................]
08A831110 00000000 00000000 00000000 00000000 [................]
可以得出结论，位于 内存的 in memory 的clumn store里。