FAQ’s: Oracle GoldenGate 12c: Part IV

Do you want to know what are the most frequently asked questions in Oracle GoldenGate?

This post covers the most common questions related to Oracle GoldenGate 12c that we get frequently from the trainees of our  Oracle GoldenGate 12c Administration course.

This blog is the fourth part of the series “FAQ’s: Oracle GoldenGate 12c”.

For previous FAQ’s Oracle GoldenGate 12c series check here:

• FAQ’s: Oracle GoldenGate 12c: Part I 
• FAQ’s: Oracle GoldenGate 12c: Part II 
• FAQ’s: Oracle GoldenGate 12c Q/A: Part III

Here are the Queries from Trainees:

Q1. What is reverse utility?
Ans: Reverse utility is used for the following purposes:
To restore a test database to its original state before the test run. Because the Reverse utility only backs out changes, a test database can be restored in a matter of minutes, much more efficiently than a complete database restore, which can take hours.

To reverse errors, caused by corrupt data or accidental deletions.

For example, if an UPDATE or DELETE command is issued without a WHERE clause, the Reverse utility reverses the operation.

Q2. In unidirectional GoldenGate setup, steps to add a table for replication?
Ans: Below are the steps to already running extract and replicates:
a) Take necessary approval to stop the Goldengate extraction and replication.
b) Stop the processes
c) Edit the parameter files and add a new table in the extract, data pump, and replicate the process.
d) Verify the changes.
e) Start the processes.

If the table in the source database already contains the data then, ensure to perform the Initial Load.

Q3. Can we change the Goldengate Oracle DB without setting up an operating system level?
Ans: Golden gate is installed at OS level outside the database. However, Goldengate setup needs some DB prerequisites to be met.

Q4. What are the types of extract checkpoint positions?
Ans: Extract checkpoint stores below information:

a) Startup checkpoint
b) Recovery checkpoint
c) Current checkpoint
d) Write Checkpoint

For checking details of checkpoint use below command at GGSCI,
GGSCI> info <extract>,showch

Q6. How to check how many records processed in replication /extraction?
Ans: Each process statistics are updated as and when records are processed. The number of records processed since the last restart of the process can be checked by using Using STATS command

GGSCI>STATS <procees-name>

OR using REPORTCOUNT Parameter

Q7. How to calculate & allocate swap space for GG server?
Ans: Swap space is located on hard drives to provide additional memory when the physical memory (RAM) is full.

To estimate the required swap space, you can:
a) Startup one Extract or Replicat.
b) Run GGSCI.
c) View the report file and find the line PROCESS VM AVAIL FROM OS (min).
d) Round up the value to the next full gigabyte if needed. For example, round up 1.76GB to 2 GB.
e) Multiply that value by the number of extracts and replicate processes that will be running. The result is the maximum amount of swap space that could be required, not that this means all the extract and replicate process processing similar transactions. If not, you need to customized space needed per each process.

Because Oracle GoldenGate only writes the committed transaction to the trail files, all of the uncommitted transactions are cached in memory. The cache requires both the physical memory (RAM) and virtual memory (SWAP space). The cache can be configured with the Oracle GoldenGate CACHEMGR (128 GB by default) parameter.

The following is an example content from Oracle GoldenGate report file for the CACHE related information:
CACHEMGR virtual memory values (may have been adjusted)
CACHESIZE: 32G
CACHEPAGEOUTSIZE (normal): 8M
PROCESS VM AVAIL FROM OS (min): 63.97G
CACHESIZEMAX (strict force to disk): 48G

From the Oracle GoldenGate documentation, the operating system must have enough swap space to run Oracle GoldenGate. Oracle recommends a minimum of 512GB for the swap and page file space [2]. Without proper setup, you will get the following error:
Checking Temp space: must be greater than 120 MB. Actual 8257 MB Passed
Checking swap space: 0 MB available, 150 MB required. Failed <<<<

Q8. How to check last 5 recent extract checkpoints?
Ans: GGSCI>info <extname>,showch

Q9. What are the recovery types in the extract process?
Ans: There are two types of recovery mode for extract:

a) Append mode: By default, Extract operates in append mode, where if there is a process failure, a recovery marker is written to the trail and Extract appends recovery data to the file so that a history of all prior data is retained for recovery purposes.

b) Overwrite mode: Overwrite mode is another version of Extract recovery that was used in versions of Oracle GoldenGate prior to version 10.0. In these versions, Extract overwrites the existing transaction data in the trail after the last write-checkpoint position, instead of appending the new data. The first transaction that is written is the first one that qualifies for extraction after the last read checkpoint position in the data source.

Q10. How to manager process to check extract/replicate lag?
Ans: LAG is reported in Goldengate by using the LAGREPORTMINUTES or LAGREPORTHOURS parameter. Use the said parameters to specify the interval at which Manager checks for Extract and Replicat lag.

If you wish to learn GoldenGate systematically then look at Activity Guides (tasks) you must perform from our Step by Step Guide to Learn Oracle GoldenGate or if you are already working/using Oracle GoldenGate then look at Oracle GoldenGate 12c Troubleshooting using Logdump Utility 

This post is from our Oracle GoldenGate 12c Administration Training, in which we cover Architecture, Installation, Configuring & Preparing the Environment, DML Replication – Online Change Synchronization, Initial Load, Zero Downtime Migration & Upgrading using GoldenGate, Oracle GoldenGate Security, Performance of Oracle GoldenGate and Troubleshooting and much more.

Related/Further Reading:

If you are just starting out in Goldengate then I highly recommend you to go through these posts first

• Oracle GoldenGate 12c Overview & Components
• Oracle GoldenGate 12c Download & Installation 
• FAQ’s: Oracle GoldenGate 12c: Part I
• FAQ’s: Oracle GoldenGate 12c: Part II
• FAQ’s: Oracle GoldenGate 12c Q/A: Part III
• Oracle GoldenGate 12c Training: Step by Step Activity Guides /Hands-On Lab Exercise
• Oracle GoldenGate 12c Administration

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