Sangam-AIOUG 2016 (11th ,12th Nov) Suvendu 12c Database Caching Sangam-AIOUG 2016 (11th ,12th Nov) Suvendu

Who am I ? Cloud Database Engineer @ AWS – Amazon 12 years of real-time industry experience (Ex- Oracle ,Ex-IBM Labs). OCM Certified ,AWS Certified Solution Arch , OCP ,RAC Certified , Oracle Linux Certified. Technical Blog (www.geopdata.com).

Caching.. Why We need caching ? Can I Fit a 100 MB Database Completely in a 100 MB Buffer Cache ?

Caching - What's new in 12.1.0.2 ? Database Caching Full Database caching (When Possible) - Default. Full Database caching (Force). (FDC) Automatic big table caching (ABTC). What if we dont have enough space in the default caching mode? Smaller tables are loaded into memory only when the table size is less than 2 percent of the buffer cache size. For medium tables, Oracle Database analyzes the interval between the last table scan and the aging timestamp of the buffer cache. If the size of the table reused in the last table scan is greater than the remaining buffer cache size, then the table is cached. Large tables are typically not loaded into memory, unless if you explicitly declare the table for the KEEP buffer pool.

Database Full Caching (Force) This is not same as ‘In-memory’ Option. Set COMPATIBLE parameter to 12.0.0 or higher. To activate FDC - Force , database must be in mount mode. To enable - ALTER DATABASE FORCE FULL DATABASE CACHING; To disable - ALTER DATABASE NO FORCE FULL DATABASE CACHING; Information about force Full Database Caching Mode is stored in the control file. Cheers – This is a free feature ,no additional licensing cost .

Cont.. Can i use ‘FDC' along with AMM (MEMORY_TARGET) or ASMM (SGA_TARGET) ? Yes, Recommended to define a minimum size using 'DB_CACH_SIZE’ What is the effect on Parallel queries ? How about LOB (No cache) data ? What happens if I do not have enough Buffer cache in Force mode ? Is FDC applicable for CDB and PDBs ? What if your database uses multiple block sizes ? What will happen if we flush the database buffer cache ? What is the impact on instance recovery ? What will happen if data will be modified ? Known Bugs ?

Automatic Big Table caching (BTC) Serial direct path reads introduced in Oracle 11g to prevent removal of large number of buffers from the buffer cache by a serial large table scan. As a result, big tables accessed via serial Full Table Scans bypass the Buffer Cache and read data from the data Files into the users’ Program Global Area (PGA). This prevents flooding of the Buffer Cache Prior to 12.1.0.2, the data in big tables can be cached in buffer cache Object Cache option Keep Pool option Oracle Database 12.1.0.2 introduces Automatic big table cache (ABTC) Automatically caches scanned big objects in the Big Table Cache – an optional section of the buffer cache reserved (DB_BIG_TABLE_CACHE_PERCENT_TARGET) for storing large objects, this helps in avoiding direct path reads. PS:In RAC , PARALLEL_DEGREE_POLICY initialization parameter also needs to be set .The value can be AUTO or ADAPTIVE. Where big table is any table larger than _small_table_threshold (= 2% of _db_block_buffers). Uses a temperature-based, object-level replacement algorithm to manage the big table cache contents instead of the traditional LRU-based (block-level replacement algorithm) Can caches partial objects when objects cannot be fully cached -Known as Thrashing Useful views : V$BT_SCAN_CACHE and V$BT_SCAN_OBJ_TEMPS

Demo

Conclusion…. No extra licensing cost for both the features. Performance benefits can be realized especially for I/O bound , Read intensive databases. Is designed primarily to enhance performance for data warehouse workloads. Logical database size (or actual used space) < Sum (Buffer cache of each database instance in RAC ) / Buffer cache of the database instance - Single instance. Logical database size < 80% of the (combined - RAC) buffer cache size(s)

Q & A Thank You ! You can reach me at suvendukumar@gmail.com