Topic : Data Guard

What is data guard in simple language?


Answer :

Your primary database is running and you want to reduce downtime because of unplanned outages. You create a replica of this primary database (termed as standby database).
You regularly ship redo generated in the primary database to standby database and apply it there. So that is our ?Data Guard? standby database and it is in a continuous state of recovery; validating and applying redo to remain in sync with the primary database.

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Your standby database was out of reach because of network issue. How will you synchronize it with primary database again?


Answer :

Data Guard automatically resynchronizes the standby following network or standby outages using redo data that has been archived at the primary.

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What is Redo Transport Services (RTS)?


Answer :

This process takes care of the transmission of redo from a primary database to the standby database.
Below is how Redo Transport Services (RTS) works:
1) Log Network Server (LNS) reads redo information from the redo buffer in SGA of PRIMARY Database
2) Log Network Server (LNS) passes redo to Oracle Net Services for transmission to the STANDBY database
3) Remote File Server (RFS) records the redo information transmitted by the LNS at the STANDBY database
4) Remote File Server (RFS) writes it to a sequential file called a standby redo log file (SRL) at the STANDBY database
** For multi-standby configuration; the primary database has a separate LNS process for each standby database.
** Two redo transport methods are supported with the LNS process: synchronous (SYNC) or asynchronous (ASYNC).

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How Synchronous transport (SYNC) can impact the primary database performance?


Answer :

SYNC guarantees protection for every transaction that the database acknowledges as having been committed but at the same time LGWR must wait for confirmation that data is protected at the standby before it can proceed with the next transaction. It can impact primary database performance and it depends on factors like
a) the amount of redo information to be written
b) available network bandwidth
c) round-trip network latency (RTT)
d) standby I/O performance writing to the SRL.
e) distance betweeen primary and standby databases as network RTT increases with distance.

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Explain the architecture of data guard?


Answer :

Data guard architecture includes the following components
Primary database - Refers to the production database.
Standby Database - Refers to a copy of primary or production database.It may have more than one standby database.
Log transport service - Manages transfer of archive log files primary to standby database.
Network configuration - Refers to the network connection between primary and standby database
Applies archived logs to the standby database.
Role management services - Manages the role change between primary and standby database.
Data guard broker - Manages data guard creation process and monitors the dataguard.

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