oracle database service ha with data guard · our company. 3 23.11.2017 trivadis doag17: oracle...
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Oracle Database Service High Availability with Data Guard?Robert BialekSenior Principal Consultant
@RobertPBialek doag2017
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Who Am I
Trivadis DOAG17: Oracle Database Service High Availability with Data Guard?2 23.11.2017
Senior Principal Consultant and Trainer at Trivadis GmbH in Munich.
– Master of Science in Computer Engineering.
– At Trivadis since 2004.
– Trivadis Partner since 2012.
Focus:
– Data and Service High Availability, Disaster Recovery.
– Architecture Design, Optimization, Automation.
– New Technologies (Trivadis Technology Center).
– Open Source.
– Technical Project Leadership.
– Trainer: O-GRINF, O-RAC, O-DG.
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Our company.
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Trivadis is a market leader in IT consulting, system integration, solution engineering
and the provision of IT services focusing on and
technologies
in Switzerland, Germany, Austria and Denmark. We offer our services in the following
strategic business fields:
Trivadis Services takes over the interacting operation of your IT systems.
O P E R A T I O N
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COPENHAGEN
MUNICH
LAUSANNE
BERN
ZURICH
BRUGG
GENEVA
HAMBURG
DÜSSELDORF
FRANKFURT
STUTTGART
FREIBURG
BASEL
VIENNA
With over 600 specialists and IT experts in your region.
Trivadis DOAG17: Oracle Database Service High Availability with Data Guard?4 23.11.2017
14 Trivadis branches and more than
600 employees.
200 Service Level Agreements.
Over 4,000 training participants.
Research and development budget:
CHF 5.0 million.
Financially self-supporting and
sustainably profitable.
Experience from more than 1,900
projects per year at over 800
customers.
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23.11.2017 Trivadis DOAG17: Oracle Database Service High Availability with Data Guard?5
Technology on its own won't help you.You need to know how to use it properly.
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Database Service High Availability – Goal
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Increase database service uptime, by:
– eliminating any single point of failure to avoid unplanned outages.
– minimizing the effect of an unplanned outage on the end user (automatic failover).
– reducing downtimes during planned outages.
Consider the whole SW/HW stack. Find the best cost/risk ratio.
StorageDatabase
Server(s)Application
Server(s)Clients
Best cost/risk
ratio
Downtime
Effort
Costs
Complexity
Availability
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Database Service High Availability – Options
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Cluster – primarily used option for service high availability:
– Real Application Clusters.
– RAC One Node.
– Cold Failover Cluster.
Data Replication – used mostly for data, rather than
service high availability:
– Data Guard (Fast-Start Failover/Global Data Services).
– GoldenGate (Global Data Services).
– Other replication technologies.
SPOF
HA
HA
HA
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Agenda
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1. Introduction
2. Configuration
3. Special Cases
4. Conclusions
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Introduction
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Data Guard
Database Service HA with Data Guard? – Introduction
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Yes, it can also be used for service high availability:
– Planned downtimes – manual switchover.
– Unplanned downtimes – fast-start failover or manual failover.
Why might we consider Data Guard for service high availability:
– Less complex than a cluster installation.
– Infrastructure requirements not that high (even local storage is sufficient).
– Not subject to additional license fees (EE license assumed).
– Additionally, many other advantages: data high availability, snapshot standby,
potentially rolling upgrade capability, ...
But, with some restrictions we need to consider...
Primary Standby
FSFO Configuration
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Database Service HA with Data Guard? – Big Picture
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Primary Target
Failover StandbyCandidate Target Failover Standbys
(optional, 12.2)
Master Observer
Backup Observers
(optional, 12.2)
...
Database Clients
Primary
RW Service
Transparency
required
(failover/
switchover)
Ping Ping Ping
Required
Primary Target
Failover Standby
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Database Service HA with Data Guard? – Monitoring
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Observer
DGMGRL – Threads
W000 B001
P001 S001
Connect
Enter PING State
PING
SLEEP
~ 3sec.
ObserverReconnect
property set and reached
Reconnect interval expired
PRIMARY
Logoff
PING
SLEEP
~ 3sec.
TARGET STANDBY
Failover condition
detected
FailoverConnect
re-tries
Timeout
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Configuration
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Data Guard Protection Modes with FSFO – Prerequisites
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▪ LogXptMode=SYNC or
FASTSYNC (12.1+)
▪ FastStartFailoverTarget(*)
▪ Flashback Database
▪ LogXptMode=ASYNC
▪ FastStartFailoverTarget(*)
▪ FastStartFailoverLagLimit
▪ Flashback Database
▪ LogXptMode=SYNC
▪ FastStartFailoverTarget(*)
▪ Flashback Database
▪ Recommended: at least 2
STDBY DBs (protection
mode downgrade!)
MaxAvailability (10.2+) MaxPerformance (11.1+) MaxProtection (12.2)
DGMGRL> EDIT CONFIGURATION SET PROPERTY FastStartFailoverThreshold = <xy>;
DGMGRL> ENABLE FAST_START FAILOVER;
All Protection Modes
FSFO: Guaranted zero data
loss.
FSFO: Data loss possible. FSFO: Guaranted zero data
loss.
Mostly used
protection mode
Value in seconds
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Fast-Start Failover – Observer (1)
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Monitoring component, initiates a failover procedure.
In 12.2, up to 3 observers (in background) can be started:
– One master and up to two backup (standby) observers.
In older releases:
– Only one running observer (HA needs to be adressed).
DGMGRL> START OBSERVER OBS1.TRIVADIS.COM IN BACKGROUND
FILE IS '$ADMIN_SID/fsfo_$ORACLE_SID.dat'
LOGFILE IS '$ADMIN_SID/fsfo_$ORACLE_SID.log'
CONNECT IDENTIFIER IS <Alias1>.TRIVADIS.COM;
W000 B001
P001 S001
Oracle wallet
required
nohup dgmgrl -logfile $ADMIN_SID/fsfo_$ORACLE_SID.log <<EOD &
CONNECT $CONNECT_DATA
START OBSERVER FILE='$ADMIN_SID/fsfo_$ORACLE_SID.dat';
EOD
Observer
PRIMARY TARGET
Failover Standby
Ping
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Fast-Start Failover – Observer (2)
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Fast start-failover is initiated by the master observer to
the target standby database, if one of the following
conditions is detected:
– observer and the target standby database cannot reach
the primary database (default: ObserverOverride=‘FALSE‘).
– user-configurable condition is met.
– DBMS_DG.INITIATE_FS_FAILOVER function has been executed.
Additonally, other pre-condidtions enforced by a protection mode need to be fulfilled:
– MaxProtection/MaxAvailability: target failover standby is in SYNC.
– MaxPerformance: FastStartFailoverLagLimit not reached for the target failover
standby.
W000 B001
P001 S001
Observer
PRIMARY TARGET
Failover Standby
Ping
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Data Guard: Role-Based Services
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For a Data Guard system, we need a role-based service,
that is running only if database has a specific role:
– Read-write service on a primary database.
– Optionally, a service on standby databases for reporting.
– Optionally, a service on snapshot standby databases.
To accomplish this task:
– Use Oracle Grid Infrastructure role-based services.
– Create your own AFTER STARTUP ON DATABASE trigger.
Database Clients
Service
R/WService
R/O
[SNAP]
?
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Data Guard: Example Role-Based Services
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Example role-based services with Grid Infrastructure.
Services are started only if database and service role match.
Depending on used client HA features (TAF, FAN/FCF, AC) additional service
properties need to be specified.
srvctl add service -db DB_SITE1 –service SRV_RW.trivadis.com -role PRIMARY
srvctl add service -db DB_SITE1 –service SRV_RO.trivadis.com -role PHYSICAL_STANDBY
srvctl add service -db DB_SITE1 -service SRV_SP.trivadis.com -role SNAPSHOT_STANDBY
SvcAgent::start 680 query_db_role
SvcAgent::start 710 not starting service srv_rw Role mismatch - Service
role:PRIMARY, current DB role:PHYSICAL_STANDBY
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Client-Side Configuration – Main Problems To Address
New network session (connect) Already established network session
Database Clients
1 IP not reachable (server/network/… issue)
2 Connect attempts
3 Wait for
connect timeout
4 Client failover
Problem
Database Clients
2 IP not reachable (server/network/… issue)
1 Connected
3 Re-connect attempts
4 Wait for
re-connect timeout
Problem
5 Client failover
ProblemProblem
CASE 1 CASE 2
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New Oracle Net Session – Connect Timeout (1)
sqlnet.ora parameters (OCI, ODP.net)
– Applies to each IP that a host name resolves to!
– All Oracle client versions supported.
For clients >=11.2:
TCP.CONNECT_TIMEOUT=3 #default 60 sec.
SQLNET.OUTBOUND_CONNECT_TIMEOUT=5 #no default
LSNR LSNR
Three-way handshake
Oracle Net
1
2
3
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OLTP.trivadis.com =
(DESCRIPTION =
(FAILOVER=ON) (LOAD_BALANCE=OFF)
(CONNECT_TIMEOUT=5)(RETRY_COUNT=3)(RETRY_DELAY=1)(TRANSPORT_CONNECT_TIMEOUT=3)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP )(HOST = italy )(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP )(HOST = sweden )(PORT = 1521)))
(CONNECT_DATA = (SERVICE_NAME = OLTP_RW.trivadis.com)))
Introduced in 12.1.0.2
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New Oracle Net Session – Connect Timeout (2)
JDBC Thin driver
– TRANSPORT_CONNECT_TIMEOUT is available beginning with 12.2 version
– To use RETRY_COUNT with 12.1.0.2, patch is required (BUG 19154304)
JDBC Thin clients can alternatively use the following driver property (ms)
– Overrides CONNECT_TIMEOUT from address description parameters
pds.setURL("jdbc:oracle:thin:@(DESCRIPTION =(FAILOVER=ON)(LOAD_BALANCE=OFF)" +
"(CONNECT_TIMEOUT=3)(RETRY_COUNT=10)(RETRY_DELAY=1)" +
"(ADDRESS_LIST = " +
"(ADDRESS = (PROTOCOL = TCP )(HOST = blue.trivadis.com )(PORT = 1521)) " +
"(ADDRESS = (PROTOCOL = TCP )(HOST = brown.trivadis.com )(PORT = 1521))) " +
"(CONNECT_DATA = (SERVICE_NAME = sales_rw.trivadis.com)))");
Properties prop = new Properties();
prop.put(oracle.net.ns.SQLnetDef.TCP_CONNTIMEOUT_STR, ""+3000);
ods.setConnectionProperties(prop);
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Established Oracle Net Session – Re-Connect Timeout
Break established network connection
without waiting for long TCP timeouts (>15 min.)
– In most cases no VIPs in use!
Using the following parameters is not a good idea:
Better solution:
– If possible use: Fast Application Notification/Fast Connection Failover.
– Tuning OS kernel parameter tcp_retries2 might be also an alternative.
LSNR LSNROracle Net
1P1
2
Client failover
4
SQLNET.RECV_TIMEOUT=30 #no default value, OCI driver
SQLNET.SEND_TIMEOUT=30 #no default value, OCI driver
prop.put ("oracle.jdbc.ReadTimeout", "5000"); //5000ms, JDBC Thin driver
Timeout
3
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Client HA Features – Overview
Transparent Application Failover:
– Can be used with Data Guard the same way (advantages/disadvantages) as with
a cluster.
Fast Application Notification/Fast Connection Failover:
– Oracle Grid Infrastructure is required to register with ONS.
– Comparing to RAC “only” rapid notification about up/down events, no workload
balancing.
Application Continuity can be used with Data Guard the same way as with a cluster:
– But requires RAC or RAC One Node or ADG (GG) option.
More about this topic:
– DOAG 2016 presentation: „Oracle Client Failover - Under the Hood”
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Special Cases
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Special Cases with FSFO: Candidate Targets Standby
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Starting with 12.2, many candidate fast-start failover target databases can be
specified, but switchover or FSFO works only to the current target standby database.
Threshold: 60 seconds
Target: db_site2
Candidate Targets: db_site2,db_site3
Observers: (*) obs1.trivadis.com
obs2.trivadis.com
DGMGRL> EDIT DATABASE db_site1 SET PROPERTY FastStartFailoverTarget =
'db_site2,db_site3';
DGMGRL> SWITCHOVER TO db_site3;
Error: ORA-16655: specified standby database not the current fast-start
failover target standby.
db_site1 db_site2 db_site3
Current target depends
on many conditions
FSFO
Switchover
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Special Cases: Switchover – DelayMins >0
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Version 11.2.0.X: recovery re-started with NODELAY option.
Version 12.1.0.X: recovery waits until DelayMins reached!
– OPEN_MODE
• Primary – CLOSED BY SWITCHOVER
• Standby – MOUNTED
– Application RW service outage within DelayMins time-frame! Application connect
attemps fail with ORA-16456: switchover to standby in progress or completed
Version 12.2.0.1: Switchover is not possible.
Error: ORA-16672: switchover not permitted to standby database with non-zero
DelayMinsFailed.
PRIMARY TARGET
Failover Standby
DelayMins>0
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Special Cases with FSFO: Master Observer Failure
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After about 31 sec. the master observer is changed, i.e.:
available backup observer is promoted to the master role.
– Note: to perform a master change, the primary database
needs to be available!
For maintenance, a master change can be performed manually.
Data Guard Broker initiated a master observer switch since
the current master observer cannot reach the primary database
Master Observer Backup Observers
DGMGRL> SET MASTEROBSERVER TO obs2.trivadis.com;
Sent the proposed master observer to the data guard broker configuration.
Please run SHOW OBSERVER to see if master observer switch actually happens.
PRIMARY
Logged on the
primary database
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Special Cases with FSFO: Failover Target Failure
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After about 10 sec. the target failover standby is changed, i.e.: a candidate
target failover standby observer is promoted to the current target role.
Note: to perform the target failover standby change, the primary database and the
master observer need to be available!
– If the master observer fails at the same time:
Permission granted to the primary database for target
switch.
The primary database returned to SYNC/NOT LAGGING state
with the standby database db_site3.db_site1 db_site2 db_site3
Observer
LGWR: FSFO SetState("UNSYNC", 0x2) operation requires an ack
Primary database will shutdown within 30 seconds if permission
is not granted from Observer or FSFO target standby to proceed
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Special Cases with FSFO: Master Observer/Primary
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If the primary and the master observer fail:
– No failover is initiated to a candidate standby.
– From a backup observer log file:
If the master observer is started at a later time, it waits until
FastStartFailoverThreshold timeout is reached again and fails over to the current
target standby.
Ready to failover check on standby returned
RFS_NON_MSTOB.
Command READY_TO_FSFO to thread S024 returned status=0
Fast-Start Failover is not possible because this
observer is not the master.
Master Observer Backup Observers
db_site1 db_site2 db_site3
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Special Cases with FSFO: Private Redo Network
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If the public network on the primary server fails:
– Broker configuration property: ObserverOverride=FALSE.
– No failover (HB over private network still works!).
In this network configuration consider using:
Fast-Start Failover is not possible because
primary last contacted the standby within
FastStartFailoverThreshold seconds
db_site1 db_site2 db_site3
Master Observer
Private Network
DGMGRL> EDIT CONFIGURATION SET PROPERTY ObserverOverride='TRUE';
Public Network
HB
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Master Observer, Primary/Standby DB: Location? (1)
Trivadis DOAG17: Oracle Database Service High Availability with Data Guard?31 23.11.2017
For DR HA service protection, do not place the primary and the master observer in
the same data center!
Data Center 1 Data Center 2
Master Observer
Primary
Backup Observer
Target Standby
No automatic
failover!
No RW application service available!
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Master Observer, Primary/Standby DB: Location? (2)
Trivadis DOAG17: Oracle Database Service High Availability with Data Guard?32 23.11.2017
For DR HA service protection, do not place the primary and the master observer in
the same data center!
Data Center 1 Data Center 2
Backup Observer
Target Standby
Automatic
failover!
RW application service available!
Master ObserverMaster observer placement correction monitoring:
DGMGRL> SET MASTEROBSERVER TO …
Candidate
Target StandbyPotential placement
problem!
Primary
To relocate:
Disable & Enable
FSFO
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Conclusions
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Conclusions (1)
Can Data Guard be a good solution for database service high availability?
– Yes, with a fast-start failover configuration.
– Anyway, it is not a replacement for a cluster but rather an alternative.
– Careful business requirements analysis is necessary.
Advantages:
– It offers a good service high availability, in addition to excellent data high
availability and some other features.
– Fairly simple solution (setup and operation).
– Not subject to additional license fees (EE license assumed).
– Infrastructure requirements not that high as for a cluster.
– Most client HA features can be used the same way as with a cluster.
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Conclusions (2)
Disadvantages:
– Component placement is critical and requires customized monitoring scripts.
– Some technical restrictions like network latencies (SYNC), flashback database or
force logging might limit Data Guard in this area.
– Re-connect timeouts without FAN/FCF (no VIPs).
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