Redo Waits Kyle Hailey

#.2 Copyright 2006 Kyle Hailey Log File Waits  Redo is written to disk when  User commits  Log Buffer 1/3 full (_log_io_size)  Log Buffer fills 1M  Every 3 seconds  DBWR asks LGWR to flush redo  Sessions Commiting wait for LGWR

#.3 Copyright 2006 Kyle Hailey Log File Waits : Diag REDO Log Files Data Files DBWR LGWR User2 User1 User3 Log Buffer Buffer Cache Log Buffer Buffer Cache SGA Library Cache

#.4 Copyright 2006 Kyle Hailey Typical Log Waits  Log Buffer Space  Log File Sync  Log File Switch Completion  Log File Switch (checkpoint incomplete)  Log File Switch (archiving needed)  Switch Log File Command

#.5 Copyright 2006 Kyle Hailey log buffer space  #11 Top Wait  No p1, p2, p3 parameters  Waiting for space in the redo log buffer in SGA

#.6 Copyright 2006 Kyle Hailey Log Buffer Waits REDO Log Files Data Files Log Buffer DBWR LGWR Buffer Cache User2 User1 User3 InsertUpdatedelete Log Buffer Buffer Cache SGA Library Cache

#.7 Copyright 2006 Kyle Hailey log file sync  #2 Top Wait  Wait for redo flush upon:  Commit  Rollback  Arguments  P1 = buffer# in log buffer that needs to be flushed  P2, P3 not used

#.8 Copyright 2006 Kyle Hailey log file sync  Arguments  P1 = buffer# in log buffer that needs to be flushed  P2 = not used  P3 = not used

#.9 Copyright 2006 Kyle Hailey Log File Sync REDO Log Files Data Files DBWR LGWR User2 User1 User3 Commit; wait for LGWR Log Buffer Buffer Cache SGA Library Cache

#.10 Copyright 2006 Kyle Hailey Log file switch completion  #12  No p1,p2,p3  Wait for lgwr to switch log files when generating redo

#.11 Copyright 2006 Kyle Hailey Log File Switch Log File Switch steps  Get next log file from control file  Get Redo Copy and Redo Allocation latch  Flush redo  Close File  Update Controlfile  Set new file to Current  Set old file to Active  If in Archivelog mode add file to archive list  Open all members of new logfile group  Write the SCN to the headers  Enable redo log generation

#.12 Copyright 2006 Kyle Hailey log file switch completion REDO Log Files Data Files Log Buffer DBWR LGWR Buffer Cache Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Wait : log file switch completion User2 User1 User3 User2 User1 User3 Commit; Wait for LGWR Log Buffer Buffer Cache SGA Library Cache

#.13 Copyright 2006 Kyle Hailey log file switch (checkpoint incomplete)  #22  No p1,p2,p3 args  Wait for checkpoint to complete because all log files are full

#.14 Copyright 2006 Kyle Hailey log file switch (checkpoint incomplete) : Diag REDO Log Files Data Files Log Buffer LGWR Buffer Cache User2 User1 User3 Commit; Wait for LGWR Checkpoint a Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Checkpoint b Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Checkpoint c Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx Block xxxx DBWR Log Buffer Buffer Cache SGA Library Cache

#.15 Copyright 2006 Kyle Hailey Log Archiving : Diag REDO Log Files Archive Dest Log Buffer ARCH LGWR Buffer Cache Log Buffer Buffer Cache SGA Library Cache

#.16 Copyright 2006 Kyle Hailey log file switch (archiving needed)  #33  No p1,p2,p3  Database “hangs” for transactions

#.17 Copyright 2006 Kyle Hailey log file switch (archiving needed) : Diag REDO Log Files Archive Dest ARCH LGWR User 2 User 1 User 3 Commit; Wait for LGWR Log Buffer Buffer Cache Log Buffer Buffer Cache Log Buffer Buffer Cache SGA Library Cache

#.18 Copyright 2006 Kyle Hailey switch logfile command  #31  Same as log file switch completion but the command is executed by the dba  Alter system switch logfile;

#.19 Copyright 2006 Kyle Hailey Summary Log Waits  Log Buffer Space : increase log buffer  Log File Sync : reduce commits  Log File Switch Completion : increase log size  Log File Switch (checkpoint incomplete) : add log files  Log File Switch (archiving needed) : make room on archive log dest  Switch Log File Command

#.20 Copyright 2006 Kyle Hailey Recovery and Checkpoints REDO Log Files Data Files DBWR LGWR Log Buffer Buffer Cache SGA Library Cache Incremental Checkpoint Current Position Needed for Recovery

#.21 Copyright 2006 Kyle Hailey DBWR dirty List and LGWR Buffers Checkpoint a Block xxxx Block xxxx Block xxxx Block xxxx LGWR DBWR Checkpoint Blocks can be scattered about LRU list Current Position Incremental Checkpoint

#.22 Copyright 2006 Kyle Hailey DBWR dirty List and LGWR MRU - Hot LRU - Cold Buffer Headers Session Shadow Dirty List Block xxxx Block xxxx Block xxxx Block xxxx DBWR Dirty Blocks are from the cold end

#.23 Copyright 2006 Kyle Hailey DBWR dirty List and LGWR MRU - Hot LRU - Cold Buffer Headers Dirty List Block xxxx Block xxxx Block xxxx Block xxxx DBWR Checkpoint a Block xxxx Block xxxx Block xxxx Block xxxx Write List Block xxxx Block xxxx Block xxxx Block xxxx Data Files

#.24 Copyright 2006 Kyle Hailey Recovery – Incremental Checkpoints  LOG_CHECKPOINT_INTERVAL = X  Lags no more tha X blocks (usually 512)  No more than 90% of smallest log file  LOG_CHECKPOINT_TIMEOUT = X  Lags no more than X seconds  DB_BLOCK_MAX_DIRTY_TARGET  Limits dirty blocks in the SGA  FAST_START_IO_TARGET (8i)  Limits dirty blocks in SGA, depricated  FAST_START_MTTR_TARGET (9i) ***  Limits recover time to seconds

#.25 Copyright 2006 Kyle Hailey Recovery – Incremental Checkpoints 9iR2  Don’t set  LOG_CHECKPOINT_INTERVAL = 0  LOG_CHECKPOINT_TIMEOUT = 0  FAST_START_IO_TARGET = 0  FAST_START_MTTR_TARGET  Seconds to Recovery, default 300 on 9i  Is overridden by FAST_START_IO_TARGET  Is overridden by LOG_CHECKPOINT_INTERVAL