© 2009 IBM Corporation Information Management Informix Dynamic Server 11.50 Continuous Availability Feature (CAF) Ron Privett KC IIUG Tech Day - 01/22/2009

© 2009 IBM Corporation

Information Management

Informix Dynamic Server 11.50Continuous Availability Feature (CAF)

Ron Privett

KC IIUG Tech Day - 01/22/2009


Informix Dynamic Server 11.50 | Continuous Availability Feature (CAF) © 2009 IBM Corporation

Agenda

Overview of CAF (MACH11)

Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR

Updatable Secondary Servers (11.50 and above)

Demo



What is CAF?

CAF = Continuous Availability Feature (Code name = MACH11)

Multi-Node Active Cluster for High Availability:– Extends HDR to support multiple secondary instances

– CAF is a cluster of IDS instances working together on a common set of data to provide 1)High availability, 2) Load balancing and 3) Disaster recovery solutions.

– CAF clusters includes one primary instance and one or more secondary instances including HDR, SDS and RSS secondary servers.

– New types of secondary servers introduced with a CAF cluster

– Shared Disk Secondary (SDS)

– Remote Standalone Secondary (RSS)

– Continuous Log Restore (CLR) **

– All secondary server instances in a CAF cluster can be configured to support DML operations.

** not exactly a CAF instance but included for the purposes of discussion



Agenda


Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR


Demo



High-Availability Data Replication (HDR) Two identical instances on two very similar physical servers:

– Primary instance

– Secondary instance

Primary physical server:– Duplicate of Primary instance structure

– All database activity – insert/update/deletes, are performed on this instance

– Sends logs to secondary server

Secondary physical server:– Read only instance: allows read only operations

– Always in recovery mode

– Receives logs from primary instance and replays them to keep in sync with primary

Primary

Blade Server A

Building-A

Blade Server B

HDR Secondary

Client Apps HDR Traffic

When primary instance goes down, secondary instance takes over as updatable instance



High-Availability Data Replication (HDR) - Review Requires same Database/Hardware/OS Synchronous or Asynchronous Only Logged Databases are replicated Data in dbspaces and sbspaces supported Blobspace Data not supported All built-in and extended data types supported Ontape or OnBar for Recovery Automatic or Manual failover Encrypted communications available Index Shipping or Index Logging



HDR - How it works…

Primary Secondary

LoggedI/O Activity

Log Buffers

Read Only



Agenda


Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR


Demo



Shared Disk Secondary (SDS)

HDR on top of a shared disk subsystem

Primary transmits the current Log Sequence Number (LSN) as it is flushing logs

SDS instances receives the LSN from the primary and reads the logs from the shared disks

SDS instances applies log changes to its buffer cache

SDS instances resynch processed LSN to primary

Primary SDS SDS

LSNACKLSN

Shareddisk

Diskmirror



Remote Standalone Server (RSS)

Similar to HDR: – Maintains a full disk copy of the database.

– Created by performing a backup/restore of the instance

– Can be used for: Additional Backup, Report processing, Load balancing.

Distinct from HDR:– Uses full duplex communication (SMX)– better throughput over slower lines.

– Does not support SYNC mode, not even for checkpoints.

– Can not currently be ‘promoted’ to primary – but can be promoted to HDR secondary (Focus is on 24 X 7 Availability, Scalability, and Disaster Recovery).

– There can be any number of RSS instances.

– Requires Index Page Logging be turned on.

RSS can be used in combination with HDR secondary:– RSS can be converted into HDR secondary.

– HDR secondary can be converted into RSS.

Primary

RSS

RSS RSS



Agenda


Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR


Demo



Continuous Log Restore (CLR)

Also known as “Log Shipping”.

Allows logical recovery to span multiple ‘ontape/onbar’ commands.

Provides a secondary instance with ‘log file granularity’.

Does not impact the primary server.

Can co-exist with “the cluster” (HDR/RSS/SDS) as well as ER.

Can be automated by scripting the log backup alarms.

Useful when backup site is totally isolated (i.e. no network)

Primary

CLR1

CLR2

CLR3




An enhancement to both ontape and OnBar– When logs are full and backed-up, the log files can be copied to other supporting

instances in CLR mode

Logs are applied to target instances as needed– Manually - as part of daily or weekly activities

– Automatically - as set by a TASK, or other processes

– ontape -l -C

– onbar -r -l -C

Note: A general assumption here is that the source server will archive logs to disk files, rather than tapes



Example of CLR Customer has immediate failover (HDR) in local

office but also wants an offsite copy. Network outages are common, and throughput is too erratic for RSS.

OR Customer needs to be able to recover quickly

but doesn’t want / need immediate failover

Customer uses O/S utilities to transfer logs and backups as needed. CLR instance can be up or not. Backups and logs can be applied to instance as business rules dictate.

HDR Secondary

HDR Primary

HD

R


Continuous LogRestore Server



Advantages of using a CLR server

Verification of Logical Restore– Archecker verifies the physical restore, a CLR server can verify the logical restore

Faster Recovery Time– If you need to restore your entire instance, having a CLR server means you could be back up and

running faster

Manual or Automatic application of Logical Logs– If you have ever dropped a production table, which hits the HDR server, or another RSS server

before you can break the connection? With a CLR server, you decide when to apply the logical log files.

Another server in case of Disaster– Can you ever have too many DR servers?



CLR Issues to be aware of…

CLR is designed to assist Disaster Recovery, not designed as a High Availability solution. However, you can ‘promote’ a CLR server into an HDR secondary server (details on the next slide).

There is no Point-In-Time restore with CLR, it’s the whole log or nothing. More a Point-In-Log restore.

To aid the process of log movement between source and target servers - consider the following:

– Using the environment variable IFX_ONTAPE_FILE_PREFIX to set the filename of ontape ‘backup to directory’ files.

– Using a shared disk to store archive files

– Script the process of removing old ‘applied’ log files to back them up to tape or other archive media.



CLR Promotion into an HDR Secondary

If needed, you could promote a CLR server into an HDR secondary server. Here are the steps:

– Break HDR with the current secondary server

– On Primary: onmode -d primary {secname}

– On Secondary:onmode -d secondary {priname}

Primary server sees the secondary needs recovery, and will start sending logs:

20:32:56 DR: Secondary server needs failure recovery Secondary sever recovers the logs and becomes available

20:33:02 DR: HDR secondary server operational



Agenda


Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR


Demo



Updatable Secondary Server

INSERT, UPDATE and DELETE statements are now supported at SDS, HDR and RSS secondary servers.

New ONCONFIG Parameter “UPDATABLE_SECONDARY” introduced in 11.50 to support DML operations at secondary server. Default setting is 0 which means that the secondary server doesn’t allow any DML

Statements.

Any setting greater than 0 enables DML Statements on the local server acting as a secondary server.

Restrictions– DDL Statements like CREATE TABLE, CREATE PROCEDURE are still not

supported

– Update Statistics is not supported.



Updatable Secondary Server

Redirects an attempted DML operation from the secondary by a pool of proxy threads via SMX interface to the primary database server for execution.

Triggers and constraint checking is performed on the primary database server.

Uses optimistic concurrency to avoid updating a stale copy of the row.

Redirected writes work on the basic data types, UDTs, logged smart BLOBs, and partition BLOBs.

Supports temp tables- both explicit and implicit.

Works on HDR secondary, RSS nodes, and SDS nodes.



How to configure an Updatable Secondary

New ONCONFIG Parameter “REDIRECTED_WRITES” in 11.50.xC1.

From 11.50xC2 onwards “REDIRECTED_WRITES” ONCONFIG parameter is renamed to “UPDATABLE_SECONDARY”.

– Default setting of the new parameter is 0 which means that the database server doesn’t allow any DML Statements in case it acts as a RSS, HDR Secondary or SDS.

– Any setting larger than 0 enable DML Statements on the local server acting as a secondary. Server is then configured as a updatable secondary.

– The setting of the Value bigger than 0 also specify how many SMX network connections to be used for distributed write operations.

Parameter setting for the UPDATABLE_SECONDARY is permanent for the uptime of the database server, means no on demand change of the current value with onmode –wf/wm is possible.



Differences in server behavior

Local database server acts as an updatable secondary enabled by UPDATABLE_SECONDARY 1

update customer set fname=“XXXXX” where customer_num=110

1 row(s) updated.

Default read only behavior by unset UPDATABLE_SECONDARY in ONCONFIG or a setting to 0

update customer set fname=„XXXX“ where customer_num=110

346: Could not update a row in the table.

140: ISAM error: operation illegal on a DR Secondary



New SQL error codes returned by the server

Using Redirected Writes on a secondary database server can cause new SQL error codes.

– Error –7350

– An attempt was made to update an invalid version of the current row or the schema of the table doesn’t match with the schema of the primary database server.

7350: Attempt to update a stale version of a row

Error in line 1

Near character position 29

Database closed.

– Error –7351

– The connection between the updatable secondary and the primary database server are lost during the execution of the current request or transaction.



Agenda


Type of CAF Servers

– HDR Secondary

– SDS and RSS

– CLR


Demo

Documents

© 2009 IBM Corporation Information Management Informix Dynamic Server 11.50 Continuous Availability Feature (CAF) Ron Privett KC IIUG Tech Day - 01/22/2009