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Gaurav Kumar
Technical Architect
About
I will be the technical interface to the customers for resolution of all kinds problems related to the OneDB database. With over 11 years of working experience on the multiple database is an added advantage to the OneDB Support group. As a member of the Support organization, my focus is to deliver post-sales support and solutions to the OneDB customer base.
Posts by Gaurav Kumar
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Data Management | October 1, 2020
How Open Global Transactions Make Your Secondary Stuck in Fast Recovery And How To Terminate Those Global Transactions
What is Global Transaction? A global transaction is a transaction that involves more than one database server. HCL OneDB database servers support two types of global transactions: TP/XA with a transaction manager and two-phase commit. HCL OneDB uses a two-phase commit protocol to ensure that distributed queries are uniformly committed or rolled back across multiple database servers. Global Transaction needs to be terminated when your secondary server is stuck in Fast recovery mode and is not coming online. So, we need to locate and terminate global transactions. Sometimes, GT can be terminated gracefully or not, based on their FLAGs. Scenario 1: Restarting Updateable secondary after a crash will get stuck in fast recovery mode until all open transactions are processed. Global transaction can be terminated gracefully. In this scenario, your Updateable secondary was crashed due to several reasons and upon starting, it gets stuck in fast recovery mode. The message below is in online.log of sds node: 12:13:04 Started processing open transactions on secondary during startup The secondary will not be operational until all the global transactions were cleared. The message above shows it is incomplete. The secondary will allow new sessions only if you see the completed string in the log. 20:10:05 Finished processing open transactions on secondary during startup. Example In the below example SDS was stuck in FR mode for almost 8 hours. We should look for the output of onstat –G from both primary and secondary. They should have different addresses in memory, but they can be identified by the "data" column. The Flag should have ‘H’ at the 3rd position, which means it was heuristically rolling back or rolled back. We can zap them using onmode –H 0x61fbe988 and onmode -H 0x61fbecf0 on SDS node. Immediately you will see your SDS will be in operational...
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Data Management | October 1, 2020
Save Your Money Using Data Compression
What is Compression By minimizing the disk space that is used by your data and indexes, it’s easy to save money Helps improving I/O Ability to store data rows in compressed format on disk Saves up to 90% of row storage space Ability to estimate possible compression ratio Fits more data onto a page Fits more data into buffer pool Reduces logical log usage How IDS Storage Optimization works! By considering the entire row and all its columns IDS looks for repeating patterns and stores those patterns as symbols in a compression dictionary By considering the entire row and all its columns IDS looks for repeating patterns and stores those patterns as symbols in a compression dictionary Creating a compression dictionary Compressing the data in table After creating the dictionary, IDS starts a background process that goes through the table or fragment and compresses the table or fragment rows. The process compresses each row and leaves it in the page where it was compressed. Any new rows that are inserted or updated are also compressed. This compress operation runs while other transactions and queries are occurring on the table. Therefore, IDS performs the operation in small transactions and holds locks on the rows being actively compressed for only a short duration. Reclaiming free space After all the rows have been repacked, the shrink operation removes the unused table or fragment space and returns free space to the dbspace that contains the table or fragment. What we are using behind the scene! Lempel-Ziv (LZ) based algorithm – static dictionary, built by random sampling Frequently repeating patterns replaced with 12-bit symbol numbers Any byte that does not match a pattern is also replaced with a 12-bit reserved symbol number Patterns can be up to 15 bytes long Max possible compression = 90%...
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Data Management | October 1, 2020
Power of duplication & high availability with HCL OneDB
Power of duplication Some businesses assume that a robust backup schedule is enough to keep their business running in the event of a disaster. These same organizations often believe that data replication systems are too: Complex Expensive Simply beyond their requirements. Fortunately, all three of these beliefs (Complex, expensive & beyond requirements) are wrong. Here are the top 5 reasons why every business needs a data replication solution: 1. Maximizing Systems Availability 2. Reduced Time to Recovery 3. Lower Costs in the Event of Outage or Disaster 4. Fully Accurate Data Copies 5. Improved Data Protection High-Availability Data Replication (HDR) HDR is the oldest replication technology since IDS version 6. Consists of a pair of servers — the primary and the HDR secondary. 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 HDR - Strength's Shared Disk Secondary (SDS) The primary server and the SD secondary server share the same disk or disk array. Servers must be configured to access shared disk devices that allow concurrent access. If the SD secondary server instance and the primary server instance both are located on a single machine, then both servers can access local disks. If they are on separate physical machines, then they must be configured to access shared disk devices that appear locally attached. SD secondary servers can be used in conjunction with HDR secondary servers, with RS...
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Data Management | September 29, 2020
How to Install HCL OneDB
Preparing for installation Before you install OneDB® database server products, you must prepare your system and plan for choices that you must make during the installation process. About this task Preparing for installation includes reviewing system requirements, planning how to upgrade, deciding on the installation owner and the installation directory, reviewing installation options, and gathering information if you want to create a database server during installation. It also includes preinstallation tasks such as obtaining the software and reviewing the machine notes. To prepare for installation: Obtain the software and configure a License Server to obtain licenses to run HCL OneDB. For more information about HCL OneDB visit, https://www.hcltechsw.com/products/onedb. Review the HCL OneDB components that can be installed with the database server. You can install all or some of them. 3. Ensure that your computer meets the system requirements. 4. Choose a user account with which to install the product. The user account becomes the installation owner. UNIX, Linux, Mac OS X: Decide between a non-root owner and an owner with root or administrative privileges. If you plan to install as an administrative user, decide on a password for user Informix 5. Choose an installation directory. If the database server is already installed, decide on the upgrade path. 6. Decide between a typical or custom installation. Choose a typical installation in the following cases: For default server features, language support, extensions, and tools. To create a configured database during installation with connectivity for JSON applications and multiple storage spaces for data.       b.   Choose a custom installation if you want to have any of the following options: To install a subset of database server components. In root-based installation, to set up event auditing for the security policies of your organization. To create a configured database server during installation with one storage space...
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Data Management | September 29, 2020
Getting familiar with HCL OneDB
Below are some basic HCL OneDB commands which might help you get familiar with the database. oninit -vy oninit -vy is to start the engine where ‘v’ means in verbose mode and ‘y’ is for yes. There are many other options to start the engine in different modes. You can explore the options using oninit – command for help 2. onmode -kuy onmode -kuy is used to stop the engine where ‘k’ means kill, ‘u’ means user sessions and ‘y’ means yes. There are many options where onmode utility is used. You can run onmode – for the utility help 3. onstat - The onstat - command displays only the output header and the value that is returned from this command indicates the database server mode. The header takes the following form: Version--Mode (Type)--(Checkpnt)--Up Uptime--Sh_mem Kbytes Version Product name and version number Mode Current operating mode (Type) If the database server uses High-Availability Data Replication, it indicates whether the type is primary or secondary. If the database server is not involved in data replication, this field does not appear. If the type is primary, the value P appears. If the type is secondary, the value S appears. (Checkpoint) Checkpoint flag If it is set, the header might display two other fields after the mode if the timing is appropriate: (CKPT REQ) Indicates that a user thread has requested a checkpoint. (CKPT INP) Indicates that a checkpoint is in progress. During the checkpoint, access is limited to read only. The database server cannot write or update data until the checkpoint ends. Uptime Indicates how long the database server has been running. If the system time is manually changed to the past and the server start-up time is later than the current system time, the uptime is not available. In this situation, the header displays the text  Uptime...
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Data Management | September 24, 2020
The onunload and onload utilities
The onunload and onload utilities The onunload and onload utilities provide the fastest way to move data between computers that use the same database server on the same platform. For example, your site purchases a more powerful UNIX computer to allow faster access for users. You need to transfer existing databases to the new database server on the new computer. Use onunload to unload data from the first database server and then use onload to load the data into the second database server. Both database servers must have the same version number, or they must have compatible version numbers. You can move an entire database or selected tables only, but you cannot modify the database schema. The onunload utility can unload data more quickly than either dbexport or the UNLOAD statement because onunload copies the data in binary format and in page-sized units. The onload utility takes a tape or a file that the onunload utility creates and re-creates the database or the table. The onunload and onload utilities are faster than dbimport, dbload, or LOAD but are much less flexible and do not let you modify the database schema or move from one operating system or database server version to another. You can use only onunload and onload if your answer to each of the following questions is yes. If your answer is no, you cannot use onunload and onload. Is the target database server on the same hardware platform? Do you want to move to another database server of the same version? Do you want to keep the existing database schema without modifying it? Do you want to move an entire database or an entire table? Are the page images compatible? Are the numeric representations the same? When you can’t use the onunload and onload utilities Because the...
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