|
Non RAC Specific
Parameters
|
RAC Specific
Parameters
|
|
MMON
|
LMSN
– Global cache service process
|
|
SMON
|
LMON
– Global Enqueue Server Monitor
|
|
PMON
|
LMD
– Global Enqueue service Daemon
|
|
CKPT
|
LCK
– Lock Process
|
|
LGWR
|
DIAG
- Diagnostic
|
|
DBWR
|
|
|
RECO
|
|
|
ARCH
|
|
|
MMAN
|
|
|
MMNL
|
|
Private Interconnect: It is a high bandwidth & low latency communication
setup used for transferring cluster specific heartbeat messages.
In
RAC environment, cluster Interconnect can also be used for some high level
operations like:
1.
Used for
indentifying the health, status and message synchronization between all the
nodes of the cluster.
2.
Used for
maintaining the global resource lock request within the cluster.
3.
Heavily used for
transferring the oracle data blocks from one instance buffer cache to other
instance buffer cache.
4.
The more the
inter instance update will increase more traffic on the network, that’s why is
it recommended to have high bandwidth for the cluster interconnect and that
could be vendor specific
Global Resource Directory- GRD:
1.
It is new memory
component and is a part of shared pool and we can find only in RAC specific
instances.
2.
Oracle
automatically maintains GRD consistency among all the nodes of the cluster
3.
GRD maintains
metadata information of the blocks which are present in database buffer
cache(DBBC)
4.
GRD Information
like:
a.
SCN #
b.
DBA- Data Block
Address/ Data Block Identifier
i.
It is a
combination of file id + block id
c.
Location of the
most recent version of the block.
d.
Mode of the
block:
i.
NULL(N) : It
indicates that no access rights are available and the block can be accessed
locally
ii.
SHARED (S): it
indicates that access rights are available and block can be accessible by multiple
instances.
iii.
EXCLUSIVE(X):
It indicates that block can be accessible by only one instance exclusively,
basically during DML operations.
e.
Role of the
block:
i.
LOCAL(L): It indicates
that the block image is present in only one instance
ii.
GLOBAL (G): it
indicates that the block image is present in multiple instances.
f.
Type of the block
image:
i.
Current (CURR)
ii.
Consistent read
(CR)
iii.
Past image (PI)
GRD
Example:
|
|
SCN#
|
DBA
|
Location
|
Mod of the block
|
Role of the block
|
Type of the image
|
|
U1 (user1 : Select statement from instance 1) N1
(node1)
|
125
|
1521
(fileid:15, block id:21)
|
N1 – Node1
|
Null (N)
|
Local (L)
|
CURR
|
|
U1 (User1: issued an update statement)
|
128
|
1521
|
N1
|
N à
X
Null to exclusive mode
|
L
|
PI-Past image
CURR à CR
Cache fusion
|
|
U2(user2: update statement on same table form node2)
|
135
|
1521
|
N2
|
XàSàX
|
G
|
CURRà
CR
|
GRD
internally maintains by coordinating GES
& GCS.
Global Enqueue Service – GES: It coordinates with global resource lock request and
non cache (other the DBBC) fusion by using LMC & LCK background processes
Global Cache Services – GCS: It coordinates with cache fusion operations with the
help of LSMn background process
Cache Fusion:
-
It is the process
of transferring the available data blocks from one instance to buffer cache to
another instance buffer cache
-
It is to avoid
more costly hardware intensive disk I/O.
o
Disk read à millisecond
o
Cache read à nanosecond
-
It has two
phases:
o
Cache fusion
phase1 was supported with oracle8i, OPS for only read operations, still I/O has
to happen for DML operations
o
From 9i, RAC
onwards cache fusion phase2 was introduced for both data read & DML
operations.
LMSn – Global Cache Service Process:
-
It is responsible
for transferring the data blocks from 1 instance to another instance buffer
cache.
-
This process can
be controlled by the parameter “GCS_SERVER_PROCESSES”
GCS_SERVER_PROCESSES =
1 (Default)
=
10 (9.2)
=
20 (10.1)
=
36 (10.2) [0-9 & a-z]
Note: Cache fusion operations we can call It as cache
coherent technique or soft ping where as disk read we can call as hard ping.
LMON - Global Enqueue Server Monitor:
-
It is responsible
for maintaining the consistency for GRD among all the instance of a database
-
It is also
responsible for GRD recovery for the failed instance.
LMD – Global Enqueue Service Daemon:
-
It is responsible
for maintaining global resource lock requests i.e... Requests for the resource
which are coming from the other instances. It will process them and maintain a
queue
LCK – Lock Process: It is responsible for non cache fusion operations
DIAG: It is responsible for updating the diagnostic information in alert log
files & trace files whenever server process or any other background
processes need diagnosis.
