LGWR写redo的伪代码

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LGWR写redo的伪代码

 

while(1)
{
/* The RBA can be stored into rba_pga; The pic keeps meta-data
   corresponding to each write. */

Read RBA corresponding to end of last write issued and store into rba_pga;
	for (each strand)
	{
		/* Start address for the write and is a pointer within the 
                   strand buffer up to which the last write went to disk. 
                   The LGWR then does a dirty read of the pointer within the
                   strand buffer where the latest redo block is being allocated.
                   The range of redo from the start address  to the dirty read is
                   referred to as the  "potential range" because it will most
                   likely make it to disk. The final range within each strand that
                   together forms a consistent set of redo will be determined by 
    		   the "extend" range step under the redo alloc latch (RAL). */
  	           Pick potential range within strand that will go into the next
                   write issued to the logfile;

		kcrfa[strand#].potential_end = ptr to latest redo;
	}

	/* Bumping the SCN after picking the range in the above step makes it
           unnecessary to contract the range in the "extend" step below. 
           Range expansion  is easy because strand meta-data points to the
           start of a LWN. */
	

     Bump SCN and store into scn_pga;
	for (each strand)
	{
		/* Get redo alloc latch for strand */
Get RAL[strand#];
		kcrfa[strand#].rba = rba_pga;
		kcrfa[strand#].scn = scn_pga;
   /* This uses kcrfa[strand#].potential_end as an optimized starting
      point to traverse the forward redo block allocation links  including all blocks of redo with SCN less than scn_pga. */
      Extend strand write range to include all  redo with SCN less than
      scn_pga;
		/* Free redo alloc latch for strand */
		Free RAL[strand#];
	}
	Issue write to logfile;
}


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