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Some of the new exotic wait events in Oracle 21c …

Posted by FatDBA on November 12, 2022

Hi Guys,

Lately I was doing tests on Oracle 21c and came across few of the exotic new wait events added to Oracle 21c. I was using and have noticed few new Exadata, ASM, Dataguard, AI/ML, Exascale, Cluster, exa persistent memory, CTWR etc. specific waits were added to the database. I have also noticed some strange looking waits as well i.e. ‘Spare1′,’Spare2′,’Spare3’ ….

Being an innovation release, and since this is a beta version, there is no document available or published for the customer for any of these new waits on Metalink

Couple of new ‘Bloom Filter‘ related waits added to 21c
Bloom Filter EOF
Bloom Filter Fetch

Bunch of new Exadata ‘smart Index|Table scan’ related, User I/O classed wait events added to 21c are
cell smart index scan request
cell smart index scan: db timezone upgrade
cell smart index scan: disabled by user
cell smart index scan: pass through
cell smart table scan request
cell smart table scan: db timezone upgrade
cell smart table scan: disabled by user
cell smart table scan: pass through
cell worker online completion
cell worker retry

Few of the new machine learning & Artificial Intellegence related wait events added in 21c are
enq: AI - Seek operation
enq: AI - dequeue operation
enq: AI - lwm update operation
enq: AI - remove subscriber
enq: AI - start cross operation
enq: AI - stop cross operation
enq: AI - truncate operation

Some of the new RAC (cluster class), global cache (cache fusion) block related waits added to 21c are
gc cr block direct read
gc current block direct read

Some of the new EDSLib/EBSLib latch waits, which are used to gum the code between RDBMS and Exascale storage added in 21c are given below.
latch: EDSLib File
latch: EDSLib Message
latch: EDSLib Root
latch: EGSLib Root
latch: EGSLibDS Root
latch: EGSLibDataStore Object
latch: EGSLibDataStoreShard Object
latch: EGSLibForum Object
latch: EGSLibNet Root
latch: EGSLibSP Root
latch: EGSLibStoragePool Object
latch: EGSLibStoragePoolRing Object
latch: FOB s.o list parent latch

This is by far the most interesting one, with no name and they seem some sort of free or extra wait events names. I am familiar with few of the other ‘spare’ i.e. “enq: BS – krb spare”, “enq: SP..xx”, “enq: SX.xx.xxx“, but these are different
spare 10
spare 2
spare 3
spare 4
spare 5
spare 6
spare 7
spare 8
spare 9

Couple of new ASM related wait events were added too
enq: AM - ASM Scrubbing
enq: AM - ASM used quota calculation

Some of the new enqueue waits on Change Tracking file are
enq: CT - CTWR DBA buffer resize
enq: CT - CTWR datafile sync
enq: CT - CTWR thread checkpoint

Some of the new enqueue related waits on Exadata Persistent Memory (PMEM)
enq: FF - PMEMfs - ODM
enq: FF - PMEMfs - Param
enq: FF - PMEMfs - Resize
enq: FF - PMEMfs - aXtnd pool
enq: FF - PMEMfs - reSze pool

Hope It Helped!
Prashant Dixit


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