初探Cache Fusion对block的锁管理

本文以双节点RAC为例，揭示了在执行select及DML操作过程中，Cache Fusion在幕后是如何对block进行锁管理的。

###实例1上查询scott.t0820_1表
select * from scott.t0820_1;
ID
----------
2

select dbms_rowid.rowid_relative_fno（rowid） rfno,dbms_rowid.rowid_block_number（rowid） blkno from scott.t0820_1;
RFNO BLKNO
---------- ----------
6 255

select to_char（6,"xxx"）,to_char（255,"xxx"） from dual;
TO_C TO_C
---- ----
6 ff

select object_id,data_object_id from dba_objects where object_name="T0820_1";
OBJECT_ID DATA_OBJECT_ID
---------- --------------
15976 15976

###用到的脚本
//// get_buffer_stat.sql ////
col object_name for a10
select （select object_name from dba_objects where object_id = b.obj） as object_name,decode （state,0, "Free", 1, "XCUR", 2, "SCUR", 3, "CR", 4,"BEING READ",5, "MREC", 6, "IREC", 7, "WRITE_CLONE", 8, "PI"） state,mode_held, le_addr, cr_scn_bas, cr_scn_wrp from x$bh b where obj = 15976 and dbablk = 255 and class = 1;

//// get_resource_name.sql，获得block在GRD内存的资源名////
col hexname for a35
col resource_name for a15
set linesize 170
select b.kjblname hexname, b.kjblname2 resource_name,b.kjblgrant, b.kjblrole, b.kjblowner,b.kjblmaster,b.KJBLPKEY,b.kjblsid,b.kjblrequest from x$le a, x$kjbl b where a.le_kjbl=b.kjbllockp and a.le_addr = （ select le_addr from x$bh where dbablk = 255 and obj = 15976 and class = 1 and state <> 3）;

//// get_resource_stat.sql 获得block资源的授权访问信息，注意：因为v$dlm_ress只在block的主节点上才能查到，而v$ges_enqueue在两节点上都有，所以查询结果表示block以inst_id所指节点为主节点，inst_id=mast+1 ////
col resource_name for a34
col state for a8
col mast for 9999
col grnt for 9999
col cnvt for 9999
set linesize 160
select a.inst_id,a.resource_name, b.state, a.master_node mast, a.on_convert_q cnvt,a.on_grant_q grnt, b.request_level, b.grant_level, b.owner_node from gv$dlm_ress a, gv$ges_enqueue b where upper（a.resource_name） = upper（b.resource_name1） and a.resource_name like "%[0xff][0x6]%" and a.inst_id=b.inst_id;

//// get_master_node.sql 获得block资源的主节点 ////
col resource_name for a34
col state for a8
col mast for 9999
col grnt for 9999
col cnvt for 9999
set linesize 160
select inst_id,resource_name,ON_GRANT_Q,ON_CONVERT_Q,master_node from gv$ges_resource where resource_name like "[0xff][0x6],[BL]%";

//// get_ges_enqueue.sql 查询gv$ges_enqueue视图////
set linesize 180
select inst_id,owner_node,resource_name1,resource_name2,GRANT_LEVEL,REQUEST_LEVEL from gv$ges_enqueue where upper（RESOURCE_NAME1） like "[0XFF][0X6],[BL]%" order by inst_id,owner_node;

---实例1上执行get系列脚本
###因为之前实例1访问过这个block所以以下脚本有输出
SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 SCUR 0 000000008BFAEE38 0 0

###block的主节点在实例2上，因为MASTER_NODE=1
SQL> @get_master_node.sql
INST_ID RESOURCE_NAME ON_GRANT_Q ON_CONVERT_Q MASTER_NODE
---------- ---------------------------------- ---------- ------------ -----------
2 [0xff][0x6],[BL][ext 0x0,0x0] 1 0 1

###获得block的资源名称，只有访问过这个block的节点才能查到
SQL> @get_resource_name

HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR 0 0 1 15976 0 KJUSERNL <---KJBLPKEY等于object_id

###inst_id=1或者MAST=0都表示block的主节点在实例2上，owner_node=0、state=GRANTED及grant_level=KJUSERPR表示目前实例1读取了这个block，经实例2的允许实例1在block上加了KJUSERPR锁
SQL> @get_resource_stat.sql
INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
2 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 1 0 1 KJUSERNL KJUSERPR 0

*************
* 人工将主节点从实例2调整为实例1
*************
---在实例1上执行
###尝试将block的主节点从实例2人工调整为实例1
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug lkdebug -m pkey 15976
Statement processed.

###MASTER_NODE=0表明block 6/255的主节点为实例1

SQL> @get_master_node.sql
INST_ID RESOURCE_NAME ON_GRANT_Q ON_CONVERT_Q MASTER_NODE
---------- ---------------------------------- ---------- ------------ -----------
1 [0xff][0x6],[BL][ext 0x0,0x0] 1 0 0

###以下两个输出除了MASTER变成0，其他均和上一轮的输出保持一致
SQL> @get_resource_name
HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR 0 0 0 15976 0 KJUSERNL

SQL> @get_resource_stat.sql
INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 0 <---inst_id说明主节点是实例1，owner_node=0表示实例1曾经访问过block 6/255、并持有KJUSERPR锁

---实例2上执行get系列脚本
###实例2尚未访问过该block所以无输出
SQL> @get_buffer_stat.sql

no rows selected

###来看看实例2上此时的输出
SQL> @get_master_node.sql
INST_ID RESOURCE_NAME ON_GRANT_Q ON_CONVERT_Q MASTER_NODE
---------- ---------------------------------- ---------- ------------ -----------
1 [0xff][0x6],[BL][ext 0x0,0x0] 1 0 0 <---ON_GRANT_Q=1表示block已经被授予某个节点的访问权限

SQL> @get_resource_name

no rows selected <---因为实例2尚未访问过该block所以尚无输出

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 0

---实例2上执行block 6/255的查询、然后执行get系列脚本
select * from scott.t0820_1;
ID
----------
2

SQL> @get_buffer_stat.sql
OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 SCUR 0 000000008AFF8E28 0 0

SQL> @get_master_node.sql
INST_ID RESOURCE_NAME ON_GRANT_Q ON_CONVERT_Q MASTER_NODE
---------- ---------------------------------- ---------- ------------ -----------
1 [0xff][0x6],[BL][ext 0x0,0x0] 1 0 0

SQL> @get_resource_name
HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR 0 1 0 15976 0 KJUSERNL <---KJBLOWNER=1

###inst_id=1表示block主节点是实例1，输出的两行分别表示实例1、实例2均以读的方式访问block
SQL> @get_resource_stat.sql
INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 0
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 1

###作为主节点的实例1记录了所有访问过该block的节点信息（inst_id=1的两条记录，owner_node=0记录实例1的访问，owner_node=1记录了实例2的访问），主节点所掌握的信息在RAC里称为master metadata；而实例2只记录了自己对于block的访问（inst_id=2的那条记录），非主节点掌握的信息在RAC里被称为shadow metadata
SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL
1 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL

*************
* 人工将主节点从实例1调整为实例2，先后在实例2、实例1上发起update操作
*************
---实例2上通过执行oradebug把block 6/255的主节点再次重置为实例2，观察master metadata是否都转移到了实例2上
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug lkdebug -m pkey 15976
Statement processed.

###果然实例2对该block的记录变为了两条（inst_id=2有两条），表明主节点对应的实例上保存RAC环境里所有节点对某个block访问时持有的锁信息
SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL
2 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERPR KJUSERNL

---实例2上发起对block的更改，运行get系列脚本
SQL> @get_buffer_stat.sql
OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- ----------- ---------- ---------------- ---------- ----------
T0820_1 SCUR 0 0000000089F90298 0 0

update scott.t0820_1 set id=id+1;
commit;

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 XCUR 0 0000000089F90298 0 0
T0820_1 CR 0 00 1947380 0

SQL> @get_resource_name.sql

HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX 0 1 1 15976 0 KJUSERNL

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
2 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 1 0 1 KJUSERNL KJUSEREX 1

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---作为主节点的实例2 master metadata信息里包含了自己（OWNER_NODE=1）修改block时加的X锁

---实例1上运行get系列脚本
SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- ----------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 1947379 0

SQL> @get_resource_name.sql

no rows selected <---get_resource_name.sql脚本实质上是关联x$le、x$kjbl两张表得出实例对block施加的锁信息，没有输出是因为实例1的cache里只有CR类型的buffer，只能给自己使用，不能分享其它节点，所以无需持有任何锁

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
2 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 1 0 1 KJUSERNL KJUSEREX 1 <---只剩下了实例2 update block时留下的X锁，实例1先期加在block上的Share锁已解除

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---作为主节点的实例2 master metadata信息里包含了自己（OWNER_NODE=1）修改block时加的X锁，没有inst_id=1的记录说明实例1没有关于该block的shadow metadata

---实例1上发起对block的更改，运行get系列脚本
SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 1947379 0

update scott.t0820_1 set id=id+1;
commit;

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 XCUR 0 0000000089F95818 0 0
T0820_1 CR 0 00 0
T0820_1 CR 0 00 1947379 0

SQL> @get_resource_name.sql

HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX 0 0 1 15976 0 KJUSERNL <---KJBLOWNER=0表示实例1访问了block

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
2 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 1 0 1 KJUSERNL KJUSEREX 0 <---OWNER_NODE=0说明之前实例2修改block时加上的X锁已被释放，改为记录本次实例1修改block时的锁信息

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---因为最近一次修改block是从实例1发起，所以实例1的GRD里记录了OWNER_NODE=0（代表实例1）修改时持有的锁信息；实例2之所以会记录实例1锁修改时的锁信息是因为实例2是master node，必须记录所有访问过该block的节点信息
2 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL

---实例2上运行get系列脚本

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 1950280 0
T0820_1 CR 0 00 1947380 0

SQL> @get_resource_name.sql <---实例1发起更改后，实例2 cache里只有CR类型的buffer，只能给自己使用，不能分享其它节点，所以无需持有任何锁（实质是x$bh.le_addr=NULL所以与x$le.le_addr关联无结果）

no rows selected

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
2 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 1 0 1 KJUSERNL KJUSEREX 0

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL
2 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL

如果此时我们将block的master node再一次指回实例1，那么get_ges_enqueue.sql仅会显示inst_id=1的记录，因为实例2不再是主节点，所以没必要保存其它节点的block锁信息

*************
* 人工将主节点从实例2调整回实例1，观察v$ges_enqueue视图的内容
*************
---实例1执行
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug lkdebug -m pkey 15976
Statement processed.

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---仅有节点1（owner_node=0）的block锁信息保存在节点1（inst_id=1）上

*************
* 重启数据库后，执行update但不提交的情况下，block锁资源查询
*************
###重启数据库
srvctl stop database -d SUSEdb1 -o immediate
srvctl start database -d susedb1

---实例1、实例2分别查询scott.t0820_1表
select * from scott.t0820_1;

---实例1查询block 6/255资源上的锁持有情况，此时实例1是主节点，实例1、实例2都对block持有共享读模式的锁
SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 0
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERPR 1

---实例1执行update后不提交，紧接着运行get系列脚本
update scott.t0820_1 set id=id+1;

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 XCUR 0 0000000089F90C18 0 0
T0820_1 CR 0 00 2015904 0

SQL> @get_resource_name.sql

HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX 0 0 0 15976 0 KJUSERNL

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 0

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL

---实例2运行get系列脚本查看资源状态信息
SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- ----------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 2015903 0

SQL> @get_resource_name.sql

no rows selected <---原有的KJUSERPR锁解除

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 0

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL

---实例2 update同一条记录，
update scott.t0820_1 set id=id+1;

<----处于等待

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- ----------- ---------- ---------------- ---------- ----------
T0820_1 XCUR 0 0000000089F96198 0 0
T0820_1 CR 1 00 2016429 0
T0820_1 CR 0 00 2015903 0

SQL> @get_resource_name.sql

HEXNAME RESOURCE_NAME KJBLGRANT KJBLROLE KJBLOWNER KJBLMASTER KJBLPKEY KJBLSID KJBLREQUE
----------------------------------- --------------- --------- ---------- ---------- ---------- ---------- ---------- ---------
[0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX 64 1 0 15976 0 KJUSERNL

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERNL 0 <---如果实例1的buffer cache里有pi类型的block在，才会有这条记录
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 1 <---虽然实例2的会话因为锁而处于等待，但GRANT_LEVEL还是显示为KJUSEREX，从GC视图看不出行级锁的存在

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 0 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSERNL KJUSERNL
1 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---虽然实例2的会话因为锁而处于等待，但GRANT_LEVEL还是显示为KJUSEREX

---实例1执行get系列脚本

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 2016429 0
T0820_1 CR 0 00 2016430 0
T0820_1 CR 0 00 2015904 0

SQL> @get_resource_name.sql

no rows selected <---因为实例1的buffer里都是CR类型的block，所以这里必然返回0条记录

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 1 <---实例1的buffer cache里有pi类型的block因为checkpoint发生变成CR了，所以相比上次在实例2的执行，结果里少了OWNER_NODE=1的记录

SQL> @get_ges_enqueue.sql

INST_ID OWNER_NODE RESOURCE_NAME1 RESOURCE_NAME2 GRANT_LEV REQUEST_L
---------- ---------- ------------------------------ ------------------------------ --------- ---------
1 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL <---相比上次在实例2执行的输出少了owner_node=0、GRANT_LEVEL/REQUEST_LEVEL=KJUSERNL的记录，因为实例1上的pi block变成了CR
2 1 [0xff][0x6],[BL][ext 0x0,0x0] 255,6,BL KJUSEREX KJUSERNL

*************
* 实例1回滚后，block资源使用情况观察
*************
---实例1 执行rollback回滚刚才的更改
SQL> update scott.t0820_1 set id=id+1;

1 row updated.

SQL> rollback;

Rollback complete.

SQL> @get_buffer_stat.sql <---回滚后可看到PI出现

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- ----------- ---------- ---------------- ---------- ----------
T0820_1 PI 0 0000000089F90C18 0 0
T0820_1 CR 0 00 2016429 0
T0820_1 CR 0 00 2016430 0
T0820_1 CR 0 00 2015904 0

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSERNL 0 <---PI block保留有KJUSERNL锁，这点与CR block不同，后者没有任何锁
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 1

SQL> alter system checkpoint;

System altered.

SQL> @get_buffer_stat.sql

OBJECT_NAM STATE MODE_HELD LE_ADDR CR_SCN_BAS CR_SCN_WRP
---------- -------- ---------- ---------------- ---------- ----------
T0820_1 CR 0 00 2020380 0 <---checkpoint发生后PI变成了CR
T0820_1 CR 0 00 2016429 0
T0820_1 CR 0 00 2016430 0
T0820_1 CR 0 00 2015904 0

SQL> @get_resource_stat.sql

INST_ID RESOURCE_NAME STATE MAST CNVT GRNT REQUEST_L GRANT_LEV OWNER_NODE
---------- ---------------------------------- -------- ----- ----- ----- --------- --------- ----------
1 [0xff][0x6],[BL][ext 0x0,0x0] GRANTED 0 0 1 KJUSERNL KJUSEREX 1 <---REQUEST_LEVEL/GRANT_LEVEL均为KJUSERNL的记录消失

总结:
1、当多个节点在自己的buffer cache里拥有同一block的scur buffer时，他们对block持有的KJUSERPR类型的锁信息可以并存于GRD
2、当某节点修改了block，该block xcur类型的buffer出现在执行修改操作节点的buffer cache，其余节点只会有PI或CR类型的buffer，对于每个PI类的buffer GRD里各保留一行REQUEST_LEVEL/GRANT_LEVEL均为KJUSERNL的记录；对于CR类的buffer GRD里不保留任何锁信息本文永久更新链接地址