High-Availability Data Replication (HDR)

HDR consists of a pair of servers — the primary and the HDR secondary — and supports both synchronous and asynchronous replication modes. In synchronous mode, transactions on the primary server will not commit until it receives an acknowledgement from the HDR secondary server. Thus, the HDR secondary is immediately ready to take the place of the primary server — what is called a "hot" standby. In asynchronous mode, only checkpoints are synchronized between the primary and HDR secondary. One characteristic of HDR is that it uses a half-duplex communication protocol and thus is sensitive to network latency. This is not the case for SD and RS secondary servers.

Table 1, below, compares the server types. Table 2 lists some common ONCONFIG settings.

Table 1. Important ONCONFIG parameters for the HDR server
Configuration parameter Server type Supported Values Description
DRAUTO Primary, HDR server
  1. - Manual
  2. - Automatic failover ultimatelyretaining server types
  3. - Automatic failover ultimatelyreversing server types
  4. - Have the Connection Manager

Arbitrator control the failover

 Controls how the primary and HDR secondary behave in a failure scenario.
DRIDXAUTO Primary, HDR server
  1. - Disable automatic index repair
  2. - Enable automatic index repair
 Automatically repair an index, if the HDR secondary server detects a corruption.
DRINTERVAL Primary

-1 - Operate in synchronous mode

> 0 - Operate in asynchronous mode

 The maximum interval, in seconds, between flushing of the highavailability data-replication buffer.
HDR_TXN_SCOPE Primary

ASYNC - Commits are not synced

NEAR_SYNC - The committed transaction has been sent to the HDR secondary but not yet applied.

FULL_SYNC - The transaction has been sent and applied on the HDR secondary.

 Defines transactional synchronization in the HDR primary when DRINTERVAL is turned off. The default is NEAR_SYNC. To enable HDR_TXN_SCOPE behavior DRINTERVAL config parameter value must be set to 0.
DRLOSTFOUND Primary, HDR server <path for lost and found file> The path for the HDR lost-andfound transaction file. This file is created during a failover and contains the transactions committed on the primary but not the HDR server.
DRTIMEOUT Primary

>= 0 seconds

Default value = 30 seconds

 The time, in seconds, before a network timeout occurs. Used by DRAUTO to detect failover.