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Oracle GoldenGate Interview Questions

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by Yamuna Karumuri
Last modified: July 19th 2021

If you're looking for Oracle GoldenGate Interview Questions & Answers for Experienced or Freshers, you are at the right place.

There are a lot of opportunities from many reputed companies in the world. According to research, Oracle GoldenGate has a market share of about 9.3%. So, You still have the opportunity to move ahead in your career in Oracle GoldenGate Development.

Mindmajix offers Advanced Oracle GoldenGate Interview Questions 2021 that helps you in cracking your interview & acquire a dream career as Oracle GoldenGate Developer.

 

Types of Oracle GoldenGate Interview Questions

Top 10 Frequently Asked Oracle GoldenGate Interview Questions

  1. What Type Of Topology Does Goldengate Support?
  2. What Are The Main Components Of The Goldengate Replication?
  3. What Are The Supplemental Logging Pre-requisites?
  4. What Type Of Encryption Is Supported In Goldengate?
  5. How Do You Add Credentials To The Credential Store?
  6. How Do You Retrieve Information From The Oracle Credential Store?
  7. How Does The Replicat Works In A Coordinated Model?
  8. How Would You Look At A Trail File Using Log Dump If The Trail File Is Encrypted?
  9. What Are The Different Ogg Initial Load Methods Available?
  10. What Is The Best Practice To Delete The Extract Files In Ogg?

 

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Basic Oracle GoldenGate Interview Questions And Answers

1) What type of Topology does Goldengate support?

GoldenGate supports the following topologies.

  • Unidirectional
  • Bidirectional
  • Peer-to-peer
  • Broadcast
  • Consolidation
  • Cascading

2) What are the main components of the Goldengate replication?

The replication configuration consists of the following processes.

  • Manager
  • Extract
  • Pump
  • Replicate

3) What transaction types does Goldengate support for Replication?

Goldengate supports both DML and DDL Replication from the source to target.

4) What are the supplemental logging pre-requisites?

The following supplemental logging is required.

  1. Database supplemental logging
  2. Object-level logging

5) Why is Supplemental logging required for Replication?

Integrated Capture (IC):

  • In the Integrated Capture mode, GoldenGate works directly with the database log mining server to receive the data changes in the form of logical change records (LCRs).
  • IC mode does not require any special setup for the databases using ASM, transparent data encryption, or Oracle RAC.
  • This feature is only available for Oracle databases in Version 11.2.0.3 or higher.
  • This Capture mode supports extracting data from source databases using compression.
  • Integrated Capture can be configured in an online or downstream mode.

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6) List the minimum parameters that can be used to create the extract process?

The following are the minimum required parameters that must be defined in the extract parameter file.

  • EXTRACT NAME
  • USERID
  • EXTTRAIL
  • TABLE

7) I want to configure multiple extracts to write to the same extra file? Is this possible?

Only one Extract process can write to one extra at a time. So you can’t configure multiple extracts to write to the same exttrail.

8) What type of Encryption is supported in Goldengate?

Oracle Goldengate provides 3 types of Encryption.

  • Data Encryption using Blowfish.
  • Password Encryption.
  • Network Encryption.

9) What are the different password encryption options available with OGG?

You can encrypt a password in OGG using

  • Blowfish algorithm and
  • Advanced Encryption Standard (AES) algorithm

10) What are the different encryption levels in AES?

You can encrypt the password/data using the AES in three different keys

  1. 128 bit
  2. 192 bit
  3. 256 bit
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11) What are some of the key features of GoldenGate 12c?

The following are some of the more interesting features of Oracle GoldenGate 12c:

  • Support for Multitenant Database
  • Coordinated Replicat
  • Integrated Replicat Mode
  • Use of Credential store
  • Use of Wallet and master key
  • Trigger-less DDL replication
  • Automatically adjusts threads when RAC node failure/start
  • Supports RAC PDML Distributed transaction
  • RMAN Support for mined archive logs

12) What are the installation options available in OGG 12c?

You can install Oracle GoldenGate 12c using in 2 ways:

  • Interactive Installation with OUI – Graphical interface
  • Silent Installation with OUI – Command Interface

13) What is a Credential Store in OGG 12c?

OGG Credential Store manages Encrypted Passwords and USERIDs that are used to interact with the local database and Associate them with an Alias.

Instead of specifying actual USERID and Password in a command or a parameter file, you can use an alias. The Credential Store is implemented as an auto-login wallet within the Oracle Credential Store Framework (CSF).

14) How to configure the Credential Store in OGG 12c?

Steps to configure Oracle Credential Store are as follows:

Step 1:

By Default Credential Store is located under “dircrd” directory.
If you want to specify a different location use can specify the “CREDENTIALSTORELOCATION” parameter in the GLOBALS file.
Example: CREDENTIALSTORELOCATION /u01/app/oracle/OGG_PASSWD

Step 2:

  • Goto OGG home and connect to GGSCI.
  • cd $OGG_HOME
  • /ggsci
  • GGSCI>

15) What command is used to create the credential store?

ADD CREDENTIAL STORE

16) How do you add credentials to the credential store?

  • ALTER CREDENTIALSTORE ADD USER userid,
  • [PASSWORD password]
  • [ALIAS alias]
  • [DOMAIN domain]

Example: GGSCI> ALTER CREDENTIALSTORE ADD USER GGS@orcl, PASSWORD oracle ALIAS extorcl DOMAIN OracleGoldenGate

17) How do you retrieve information from the Oracle Credential Store?

GGSCI> INFO CREDENTIALSTORE
OR
GGSCI> INFO CREDENTIALSTORE DOMAIN OracleGoldenGate

18) What are the different data encryption methods available in OGG 12c?

In OGG 12c you can encrypt data with the following 2 methods:

  • Encrypt Data with Master Key and Wallet
  • Encrypt Data with ENCKEYS

19) How do you enable Oracle GoldenGate for Oracle database 11.2.0.4?

The database services required to support Oracle GoldenGate capture and apply must be enabled explicitly for an Oracle 11.2.0.4 database.

This is required for all modes of Extract and Replicat.

To enable Oracle GoldenGate, set the following database initialization parameter. All instances in Oracle RAC must have the same setting.

  • ENABLE_GOLDENGATE_REPLICATION=true

20) How does the Replicat works in a Coordinated Model?

In a Coordinated Mode Replicat operates as follows:

  • Reads the Oracle GoldenGate trail.
  • Performs data filtering, mapping, and conversion.
  • Constructs SQL statements that represent source database DML or DDL transactions (in committed order).
  • Applies the SQL to the target through the SQL interface that is supported for the given target database, such as ODBC or the native database interface.
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21) What is the difference between Classic and Coordinated Replicat?

The difference between classic mode and coordinated mode is that Replicat is multi-threaded in coordinated mode.

Within a single Replicat instance, multiple threads read the trail independently and apply transactions in parallel. Each thread handles all of the filtering, mapping, conversion, SQL construction, and error handling for its assigned workload.

A coordinator thread coordinates the transactions across threads to account for dependencies among the threads.

22) How do you create a COORDINATED REPLICATE in OGG 12c?

You can create the COORDINATED REPLICATE with the following OGG Command:

  • ADD REPLICATE rfin, COORDINATED MAXTHREADS 50, EXTTRAIL dirt/et

23) I have created a Replicat process in OGG 12c and forgot to specify the DISCARDFILE parameter. What will happen?

Starting with OGG 12c, if you don’t specify a DISCARDFILE OGG process now generates a dicard file with default values whenever a process is started with START command through GGSCI.

24) Is it possible to start OGG EXTRACT at a specific CSN?

Yes, Starting with OGG 12c you can now start Extract at a specific CSN in the transaction log or trail.
Example:

  • START EXTRACT fin ATCSN 12345
  • START EXTRACT finance AFTERCSN 67890

25) List a few parameters which may help improve the replicate performance?

The parameters below can be used to improve the replicate performance:

  • BATCHSQL
  • GROUPTRANSOPS
  • INSERTAPPEND

Oracle Goldengate Interview Questions For Experienced

26) What are the areas to monitor in Goldengate Replication?

The lag and checkpoint latency of the Extract, pump and Replicat processes are normally monitored.

27) What is the PASSTHRU mode used for?

In pass-through mode, the Extract process does not look up the table definitions, either from the database or from a data definitions file.

This increases the throughput of the data pump, as the object definition lookup is bypassed.

28) What are the most common reasons for an Extract process slowing down?

Some of the possible reasons are:

  • Long-running batch transactions on a table.
  • Insufficient memory on the Extract side. Uncommitted, long-running transactions can cause the writing of a transaction to a temporary area (dirtmp) on a disk. Once the transaction is committed it is read from the temporary location on the file system and converted to trail files.
  • Slow or overburdened Network.

29) What are the most common reasons for the Replicat process slowing down?

Some of the possible reasons are:

  • A large number of transactions on a particular table.
  • Blocking sessions on the destination database where non-Goldengate transactions are also taking place on the same table as the replicate processing.
  • If using DBFS, writing & reading of trail files may be slow if SGA parameters are not tuned.
  • For slow Replicat’s, latency may be due to missing indexes on target.
  • Replicat having to process Update, delete of rows in very large tables.

30) My extract was running fine for a long time. All of a sudden it went down. I started the extract processes after 1 hour. What will happen to my committed transactions that occurred in the database during the last 1 hour?

OGG checkpoint provides the fault tolerance and makes sure that the transaction marked for committed is capture and captured only once.

Even if the extract went down abnormally, when you start the process again it reads the checkpoint file to provide the read consistency and transaction recovery.

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31) I have configured Oracle GoldenGate integrated capture process using the default values. As the data load increases, I see that extract starts lagging behind by an hour (or more) and database performance degrades. How you will resolve this performance issue?

When operating in integrated capture mode, you must make sure that you have assigned sufficient memory to STREAMS_POOL_SIZE. An undersized STREAMS_POOL_SIZE or limiting the streams pool to use a specific amount of memory can cause troubles.
The best practice is to allocate STREAMS_POOL_SIZE at the instance level and allocate the MAX. SGA at GG process level as below:

  • SQL> alter system set STREAMS_POOL_SIZE=3G
  • TRANLOGOPTIONS INTEGRATEDPARAMS (MAX_SGA_SIZE 2048, PARALLELISM 4)

32) Why would you segregate the tables in a replication configuration? How would you do it?

In OGG you can configure replicate at the data at the schema level or at the table level using the TABLE parameter of extract and MAP parameter of replicate.

For replicating the entire database you can list all the schemas in the database in the extract/replicate parameter file.
Depending on the amount of redo generation you can split the tables in a schema into multiple extracts and replicates to improve the performance of data replication. Alternatively, you can also group a set of tables in the configuration by the application functionality.

Alternatively, you may need to remove tables that have long-running transactions in a separate extract process to eliminate lag on the other tables.
Let’s say that you have a schema named SCOTT and it has 100 hundred tables.

Out of these hundred tables, 50 tables are heavily utilized by the application.
To improve the overall replication performance you create 3 extracts and 3 replicates as follows:

  • Ext_1/Rep_1 –> 25 tables
  • Ext_2/Rep_2 –> 25 tables
  • Ext_3/Rep_3 –> 50 tables

Ext_1/Rep_1 and Ext_2/Rep_2 contain 25 tables each which are heavily utilized or generate more redo.
Ext_3/Rep_3 contains all the other 50 tables which are least used.

33) How can we report on long-running transactions?

The WARNLONGTRANS parameter can be specified with a threshold time that a transaction can be open before Extract writes a warning message to the ggs error log.
Example: WARNLONGTRANS 1h, CHECK INTERVAL 10m

34) What command can be used to view the checkpoint information for the extract process?

Use the following command to view the Extract checkpoint information.

  • GGSCI> info extract, shows
  • GGSCI> info extract ext_fin, showch

35) How is the RESTARTCOLLISION parameter different from HANDLECOLLISIONS?

The RESTARTCOLLISION parameter is used to skip ONE transaction only in a situation when the GoldenGate process crashed and performed an operation (INSERT, UPDATE & DELETE) in the database but could not checkpoint the process information to the checkpoint file/table.

On recovery, it will skip the transaction and AUTOMATICALLY continue to the next operation in the trail file.
When using HANDLECOLLISION GoldenGate will continue to overwritten and process transactions until the parameter is removed from the parameter files and the processes restarted.

36) How do you view the data which has been extracted from the redo logs?

The log dump utility is used to open the trail files and look at the actual records that have been extracted from the redo or the archive log files.

37) What does the RMAN-08147 warning signify when your environment has GoldenGate Capture Processes configured?

This occurs when the V$ARCHIVED_LOG.NEXT_CHANGE# is greater than the SCN required by the GoldenGate Capture process and RMAN is trying to delete the archived logs.

The RMAN-08147 error is raised when RMAN tries to delete these files.
When the database is open it uses the DBA_CAPTURE values to determine the log files required for mining.

However, if the database is in the mounted state the V$ARCHIVED_LOG. NEXT_CHANGE# value is used.
See MetaLink note: 1581365.1

38) How would you look at a trail file using log dump if the trail file is Encrypted?

You must use the DECRYPT option before viewing data in the Trail data.
List a few useful Logdump commands to view and search data stored in OGG trail files.
Below are few log dump commands used on a daily basis for displaying or analyzing data stored in a trail file.

  • $ ./logdump – to connect to the log dump prompt
  • logdump> open /u01/app/oracle/dirdat/et000001 – to open a trail file in logdump
  • logdump> file header on – to view the trail file header
  • logdump> ghdr on – to view the record header with data
  • logdump> detail on – to view column information
  • logdump> detail data – to display HEX and ASCII data values to the column list
  • logdump> reclen 200 – to control how much record data is displayed
  • logdump> pos 0 – To go to the first record
  • logdump> next (or simply n) – to move from one record to another in sequence
  • logdump> count – counting records in a trail

39) Why should I upgrade my GoldenGate Extract processes to Integrated Extract?

Oracle is able to provide faster integration of the new database features by moving the GoldenGate Extraction processes into the database.

Due to this, the GoldenGate Integrated Extract has a number of features like Compression which are not supported in the traditional Extract. You can read more about how to upgrade to Integrated Extract and more about Integrated Delivery.

Going forward preference should be given to creating new extracts as Integrated Extracts and also to upgrade existing traditional Extracts.

40) What is the minimum Database version which supports Integrated Delivery?

Oracle 11.2.0.4 is the minimum required database version that supports both Integrated extract and Integrated Replica.

41) What databases support GoldenGate Integrated Delivery?

Oracle Integrated Delivery is only available for Oracle Databases.

42) With Integrated Delivery, where can we look for the performance stats?

Yes with 12c, performance statistics are collected in the AWR repository and the data is available via the normal AWR reports.

43) What are the steps required to add a new table to an existing replication setup?

The steps to be executed would be the following:

  • Include the new table in the Extract & pump process.
  • Obtain starting database SCN and Copy the source table data to the target database
  • Start Replicat on target at the source SCN database point.

44) What does the GoldenGate CSN equate to, in the Oracle Database?

It is equivalent to the Oracle database SCN transaction number.

45) How do you create a CSV file from the Extracted data?

You will have to use the CSV Flat File Adaptor to create CSV files. The source would be the extract trail files which use the configuration of the adaptor settings to generate CSV files.

46) What is the purpose of the DEFGEN utility?

When the source and the target schema objects are not the same (different DDLs) the Replicat process needs to know the source definition of the objects. The output from the DEFGEN utility is used in conjunction with the trail data to determine which column value in the trail belongs to which column.

47) We want to set up one-way data replication for my online transaction processing application. However, there are compressed tables in the environment. Please suggest how I can achieve it.

You must use OGG 11.2 and configure the GoldenGate Integrated Capture process to extract data from compressed tables.
Note: Pre OGG 11.2 doesn’t support extracting data from compressed tables

48) We want to set up one-way data replication using Integrated Extract for my Oracle database running 10.2.0.4. Please suggest the best architecture to achieve it.

Oracle GoldenGate Integrated Capture process supports Oracle databases 10.2 and higher. But if you are running Oracle database 10.2 and want to you Oracle GoldenGate Integrated Capture process then you must configure downstream topology.

49) I am migrating my Oracle database from non-Exadata to Exadata but my source OGG software and target OGG software versions are different (Say Source is running OGG 11.1 and target is running OGG 11.2). How can I configure my OGG process to work in such a configuration?

It is recommended that all instances of Oracle GoldenGate be the same version to take advantage of the new functionality, but this is not possible all the time and is not required.

In this scenario, OGG provides a parameter called ‘FORMAT RELEASE’ which allows customers to use different versions of Oracle GoldenGate Extract, trail files, and Replicat together.
Example:

  • RmtTrail /u01/app/oracle/dirdat, Format Release 11.1

Note: The input and output trails of a data pump must have the same trail file version.

50) What are the different OGG Initial load methods available?

OGG has 2 functionalities, one it is used for Online data Replication and the second for Initial Loading.
If you are replicating data between 2 homogeneous databases then the best method is to use a database-specific method (Exp/Imp, RMAN, Transportable tablespaces, Physical Standby, and so on). Database-specific methods are usually faster than the other methods.

If you are replicating data between 2 heterogeneous databases or your replicate involves complex transformations, then the database-specific method can’t be used. In those cases, you can always use Oracle GoldenGate to perform the initial load.

Within Oracle GoldenGate you have 4 different ways to perform the initial load.

  • Direct Load – Faster but doesn’t support LOB data types (12c include support for LOB)
  • Direct Bulk Load – Uses SQL*LOAD API for Oracle and SSIS for MS SQL SERVER
  • File to the replica – Fast but the file limit is 2GB. If the table can’t be fit in 1 rmtfile you can use maxfiles but the replica needs to be registered on the target OGG home to read the rmtfiles from the source.
  • File to Database utility – depending on the target database, use SQL*LOAD for Oracle and SSIS for MS SQL SERVER and so on.

Oracle GoldenGate initial loading reads data directly from the source database tables without locking them. So you don’t need downtime but it will use database resources and can cause performance issues. Take extra precautions to perform the initial load during the non-peak time so that you don’t run into resource contention.

51) I have a table called ‘TEST’ on the source and target with the same name, structure, and data type but in different column order. How can you set up replication for this table?

 OGG by default assumes that the sources and target tables are identical. A table is said to be identical if and only if the table structure, data type, and column order are the same on both the source and the target.
If the tables are not identical you must use the parameter ‘SOURCEDEFS’ pointing to the source table definition and ‘COLMAP’ parameter to map the columns from source to target.

52) What is the best practice to delete the extract files in OGG?

Use the manager process to delete the extract files after they are consumed by the extract/replicate process

  • PURGEOLDEXTRACTS /u01/app/oracle/dirdat/et*, USECHECKPOINTS, MINKEEPHOURS 2

53) What parameters can be used to configure Oracle GoldenGate to extract data from Archived Redo log files only?

Use the TRANLOGOPTIONS ARCHIVEDLOGONLY option in the parameter file.

54) What are the basic resources required to configure Oracle GoldenGate's high availability solution with Oracle Clusterware?

There are 3 basic resources required:

  • Virtual IP
  • Shared storage
  • Action script
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About Author

author
NameYamuna Karumuri
Author Bio

Yamuna Karumuri is a content writer at Mindmajix.com. Her passion lies in writing articles on the IT platforms including Machine learning, PowerShell, DevOps, Data Science, Artificial Intelligence, Selenium, MSBI, and so on. You can connect with her via  LinkedIn