sap hana sps10- asynchronous table replication (atr)

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SAP HANA SPS 10 - What’s New? Asynchronous Table Replication (ATR)

SAP HANA Product Management June, 2015

(Delta from SPS 09 to SPS 10)

© 2015 SAP SE or an SAP affiliate company. All rights reserved. 2Public

Agenda

Motivation

Key Principles

Setup an ATR-Landscape

Query on Replica Tables

Additional Remarks


Motivation

The main objective of ATR is to balance OLTP and OLAP workload within a HANA scale-out system


Key Principles

Replication on Table-Level

A selected list of 1…n tables can be defined as replicated tables

Asynchronous Replication

Write operations on replicated tables are propagated to their replicas asynchronously

Source write transaction commits without waiting for its propagation to the replica

Transactional Replication

Cross-node transactional consistency is guaranteed by preserving the source transaction boundary and their

commit order on log replay at the replica side

Fast Replication

Propagation delay is minimized by parallel log replay by multiple replayer threads at the replica side


Setup an ATR-Landscape for OLTP and OLAP workload

Steps to setup an ATR-Landscape:

Create Replica Schema → Create Replica Tables → Activate Replication


Create Replica Tables and Table Placement

Create Replica Tables

CREATE SCHEMA REP_SCHEMA;

CREATE TABLE REP_SCHEMA.TAB1 LIKE SRC_SCHEMA.TAB1 ASYNCHRONOUS REPLICA;

ALTER TABLE SRC_SCHEMA.TAB1 ADD ASYNCHRONOUS REPLICA;

creates replica table on any replica node and add an additional replica on another available replica node

Table Placement

Option 1: Table placement rule– ALTER SYSTEM ALTER configuration ('global.ini','SYSTEM') SET ('table_placement','repl_volumes')='6,7,8' WITH RECONFIGURE;

– ALTER SYSTEM ALTER TABLE PLACEMENT (SCHEMA_NAME => 'REP_SCHEMA') SET (LOCATION => 'repl_volumes');

Option 2: Explicit Table Location – CREATE TABLE REP_SCHEMA.TAB1 LIKE SRC_SCHEMA.TAB1 ASYNCHRONOUS REPLICA AT 'host1:port1';

– ALTER TABLE SRC_SCHEMA.TAB1 ADD ASYNCHRONOUS REPLICA AT 'host2:port2';


Activation and Dropping Replica Tables

Activate /Deactivate Replication

all tables

– ALTER SYSTEM ENABLE ALL ASYNCHRONOUS TABLE REPLICAS

– ALTER TABLE SRC_SCHEMA.TAB2 ENABLE ASYNCHRONOUS REPLICA;

single tables (works only, if global replication is already enabled)

– ALTER SYSTEM DISABLE ALL ASYNCHRONOUS TABLE REPLICAS;

– ALTER TABLE SRC_SCHEMA.TAB1 DISABLE ASYNCHRONOUS REPLICA;

Drop Replication – DROP SCHEMA REP_SCHEMA CASCADE;

– ALTER TABLE SRC_SCHEMA.TAB1 DROP REPLICA AT ALL LOCATIONS;

– ALTER TABLE SRC_SCHEMA.TAB1 DROP REPLICA AT '<replica host>:<replica port>';


Monitoring Replica Tables

Monitoring Views

M_ASYNCHRONOUS_TABLE_REPLICAS

– contains the accumulated replica information for all replicated tables in the HANA system

M_ASYNCHRONOUS_TABLE_REPLICAS_RESET

– contains the accumulated replica information since the last reset of the view M_ASYNCHRONOUS_TABLE_REPLICAS

– this view also contains a timestamp field RESET_TIME, which indicates the last time the data was reset

– ALTER SYSTEM RESET MONITORING VIEW SYS.M_ASYNCHRONOUS_TABLE_REPLICAS_RESET

Check Replica Tables

– SELECT * FROM M_ASYNCHRONOUS_TABLE_REPLICAS WHERE SOURCE_SCHEMA_NAME = SRC_SCHEMA AND SOURCE_TABLE_NAME = TAB1

– Shows all replica tables created in for SRC_SCHEMA.TAB1


Query on Replica Tables

General remarks

If a client is connected, the statements are routed to the source tables by default, because the asynchronous replica might have an outdated state compared to the

source table

If the explicit schema name of the replica tables is given, the statements are routed to the replicas accordingly

Round-Robin

If there are multiple replica tables for one source table, one of the replica table is picked to service the query in the round-robin manner

SELECT * FROM REP_SCHEMA.TAB1;

Explicit connection

You can make an explicit connection to the location of a specific replica table

SELECT * FROM REP_SCHEMA.TAB1 with hint(route_to(4));

Here '4' means the volume-id of indexserver

Get the volume-id of a table replica:

SELECT V.VOLUME_ID, C.SCHEMA_NAME, C.TABLE_NAME, C.PART_ID, C.RECORD_COUNT FROM M_VOLUMES V, M_CS_TABLES C

WHERE V.HOST = C.HOST and V.PORT = C.PORT AND SCHEMA_NAME = 'REP_SCHEMA' AND TABLE_NAME LIKE '%TAB1%';


Additional Remarks

• Asynchronous table replication works only for CS-tables within a single HANA scale-out landscape. It cannot be used for replicating a table across two different HANA

landscapes or between HANA and other DBMS instances, like system replication or SLT replication

• Asynchronous table replication works also for partitioned tables, where the replica’s partitions will be created like source partitions’ node distribution

• Source table and its replica cannot be located to the same node

• Replica table cannot be created on master indexserver.

• Only one identical replica table can exist on a replica node (same for partitioned tables)

• The following table types cannot be set as a replication table: History table, Flexible table, Temporary table, Proxy table and Extended Storage table

• A source table and its replica table should have identical table structure (same for partitioned tables)

• Write operations and DDL operations cannot be executed directly on a replica table (such access will return an error

• Replication activation can take longer time for big source tables in SPS10. Further optimizations will come in the next SPS. Meanwhile, export (from source table) and

import (into replica table) is recommended to create . (detailed procedure is described in '2. Special Handling for Big CS Source Table')

https://wiki.wdf.sap.corp/wiki/display/ngdb/Public+User+Guide#PublicUserGuide-2.SpecialHandlingforBigSourceTable


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