🚀 Oracle Exadata Overview
Oracle Exadata is a super-fast, pre-built, engineered system (hardware + software together) designed to run Oracle databases much faster and more efficiently than a normal server.
🧩 Exadata Main Components
🖥️ Database Servers (Compute Nodes)
Run Oracle Database software
Handle query execution and database logic
📦 Storage Servers (Cell Servers)
✅Smart storage servers with their own CPUs and memory
✅ Process queries directly inside the storage
✅ Filter data before sending results to DB servers
✅ Reduce workload on the database layer
✅ Provide extremely fast I/O
✅This is called Smart Scan, one of Exadata’s biggest advantages.
⚡ High-Speed Network
RoCE/InfiniBand fabric ensures ultra-fast communication between servers and storage.
InfiniBand (IB) replaced with RoCE (RDMA over Converged Ethernet) Starting from X8M
The InfiniBand Subnet Manager (SM) is NOT used in the new RoCE.
RoCE Fabric Manager (RFM) => Management and monitoring software that controls the RoCE network fabric used in modern Exadata (X8M and later) systems
🌐 Management/Network Switches
Provide connectivity and manage traffic across the Exadata environment.
🛠️ Exadata Software
Specialized software stack that integrates and optimizes all components.
🗄️ Exadata Rack Types
🔧 Notes
olsnodes -n → List cluster nodes
asmcmd lsdg → Display ASM disk groups
cellcli -e "list flashcache" → Show flash cache details
./exachk → Run complete Exadata health check
Use AWR Reports to check Cell Offloading & Smart Scan Efficiency
🛠️ Exadata Tools
🔹 CellCLI
Runs locally on a storage cell to manage and monitor storage components:
Grid disks
Cell disks
Flash cache
Physical disks (NVMe, SSDs)
Cell services
Metrics and alerts
Examples:
cellcli -e "list physicaldisk"
cellcli -e "list cell detail"
🔹 DCLI (Distributed Command Line Interface)
Python-based tool for cluster-wide management:
Parallel Execution: Run commands across multiple servers simultaneously
Centralized Management: Manage the entire cluster from one location
SSH Integration: Requires passwordless SSH connectivity
Automation: Ideal for routine tasks like installs or checks
Targeting: Specify servers via node lists or group files
Examples:
dcli -g all_cells -l root "cellcli -e list cell"
dcli -l oracle -g /tmp/a.txt "ps -ef |grep pmon"
🔹 ExaCLI
Remote administration tool for Exadata:
Manage and monitor storage cells and DB nodes without SSH access
Essential for Exadata Cloud and Exadata Cloud@Customer
Provides visibility into storage-level metrics and objects
🧑💻 Key Software Features
🔹 Smart Scan
Controlled by CELL_OFFLOAD_PROCESSING (default: TRUE)
Offloads SQL processing to storage servers
Activated during full table scans or index fast full scans
Look for "TABLE ACCESS STORAGE FULL" or "STORAGE INDEX" in SQL plans
Limitation: Doesn’t work if data is on NFS, SAN, or local disk
⚡ Flash Cache Modes
Exadata flash can operate in two modes for handling writes:
Write-through → Write to disk first (safe, slower). Default in older Exadata.
Write-back → Write to flash first (fast, modern). Default in Exadata X5 and later.
Commands:
cellcli -e "LIST CELL DETAIL" | grep flashCacheMode
cellcli -e "ALTER CELL flashCacheMode=WriteBack"
cellcli -e "ALTER CELL flashCacheMode=WriteThrough"
🔹 Storage Index
In-memory metadata structure on each storage cell
Maintains min/max values of columns to eliminate unnecessary I/O
Stored only in memory (lost on reboot, rebuilt as queries run)
Storage region = 1 MB chunk of data
🔹 Exadata Hybrid Columnar Compression (EHCC)
Compression modes:
Examples:
Create table example compress for query high as select * from example2;
Alter table example compress for query high;
Alter table example move nocompress;
Organizes data into Compression Units (CUs)
Ideal for Data Warehousing / Archival
Not recommended for OLTP workloads
📊 Exadata Calibrate
Acts like a storage speed test
Command: DBMS_RESOURCE_MANAGER.CALIBRATE_IO
Measures raw disk/flash performance (IOPS, throughput)
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