A customer who had migrated from Oracle to PostgreSQL several years ago recently reported a serious performance regression. A critical table—now holding over 700 million rows—had become extremely slow when filtering by date. As an DBA, I approached this from an Oracle perspective: partition pruning, local indexes. PostgreSQL partitioning is broadly similar to Oracle’s, butContinue reading “Partitioning in PostgreSQL vs Oracle”
Tag Archives: oracle
When the Clustering Factor Strikes: How a “Perfect” Plan Turned into a 9-Second I/O Nightmare
This wasn’t a theoretical exercise—it was a real-world performance issue that left the database paralyzed.Let’s start with the global stats: The database wasn’t working—it was waiting.Over 90% of the query’s elapsed time was spent on I/O waits, meaning the database was stuck reading data from disk. Step 1: The Execution Plan At first view, theContinue reading “When the Clustering Factor Strikes: How a “Perfect” Plan Turned into a 9-Second I/O Nightmare”
Resizing an ASM Diskgroup on Exadata When OCR/Voting Files Are on It
When you try to shrink an ASM diskgroup that holds Oracle Clusterware files (OCR and voting disks), you may hit errors like: Why it happens Even though Oracle bugs 24568147 and 37688474 mention fixes in newer releases (19.27 RU+), this issue still reproduces in 19.28 and 23.8. The voting files are persisted in the ASMContinue reading “Resizing an ASM Diskgroup on Exadata When OCR/Voting Files Are on It”
Be Careful: EX80 Issue Can Wipe Out Your Exadata/ZDLRA X8/X9 Data!
Recently, our ZDLRA X8-2 was impacted by the EX80 issue, resulting in the loss of three disks within a very short time. Two of these disks were partner disks, causing the DELTA disk group to unmount and all customer data to be lost. Oracle Support confirmed that recreating the DELTA disk group was not anContinue reading “Be Careful: EX80 Issue Can Wipe Out Your Exadata/ZDLRA X8/X9 Data!”
How to fix “DROPPED” griddisk in Cell
You may encounter a situation where a grid disk is in a dropped status in oracle exadata cell storage. This issue can be identified using the following command: Additionally, the ASM alert log may show errors like: This error indicates that the grid disks do not have the same size, which is causing issues inContinue reading “How to fix “DROPPED” griddisk in Cell”
Unlocking Performance with Oracle 23AI’s True Cache
Oracle 23AI introduces a groundbreaking feature called True Cache, which provides an in-memory caching layer for frequently accessed data. This significantly improves read performance, especially in environments where quick access to repetitive data queries is critical. However, don’t confuse it with the “In-Memory” feature, as both serve very different use cases. Let’s explore the details.Continue reading “Unlocking Performance with Oracle 23AI’s True Cache”
Benefits of Zstandard Compression in Oracle 23ai HCC
In Oracle Database 23ai, significant improvements have been made to Hybrid Columnar Compression (HCC), with the default compression method now utilizing Zstandard (Zstd) instead of the previous algorithms, zlib and bzip2. But what exactly is Zstandard, and how does it differ from zlib and bzip2? Zstandard is a lossless data compression algorithm developed by YannContinue reading “Benefits of Zstandard Compression in Oracle 23ai HCC”
How to patch Exadata PDU
Recently, I collaborated with a colleague to promote our Exadata system to a new Oracle Enterprise Manager (OEM) server. However, we encountered issues when attempting to promote the Power Distribution Unit (PDU). After consulting My Oracle Support (MOS), we decided to address potential bugs by applying the latest PDU patch before proceeding with the promotionContinue reading “How to patch Exadata PDU”
What should we do if the Flash Cache is degraded in an Exadata cell
Flash cache plays a critical role in Exadata performance. When issues arise, it’s crucial to understand the symptoms and resolution steps. Typically, each flash cache comprises four flash disks. If one flash disk fails, the cell service automatically removes it while continuing to operate with the remaining three disks. In most cases, immediate intervention isContinue reading “What should we do if the Flash Cache is degraded in an Exadata cell”
ZDLRA ERROR: Filesystem label ESP is found more than once.
Recently, while patching a ZDLRA X7-2 full stack to version 21.1.202405, I encountered an error during the dbnode precheck. This blog post details the issue and its resolution. The Error During the precheck, the following error was encountered: 2024-09-17 15:13:11 +0200 :ERROR : dbnodeupdate.sh precheck failed on one or more nodes SUMMARY OF WARNINGS ANDContinue reading “ZDLRA ERROR: Filesystem label ESP is found more than once.”
Oracle DBA Insights 