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From "Raymond Raymond" <raymond_de...@hotmail.com>
Subject Re: Discussion of incremental checkpointing
Date Tue, 14 Feb 2006 20:14:16 GMT
Thanks for so many people gave their suggestions on this issue.
I really learned a lot of things from it. Since I am doing a student project
on derby, I am thinking of implementing two versions of checkpointing:

1. Let me call it "automaticaly scheduled checkpointing". In this version,
I will not change lots on the checkpointing mechanism. I will add a module
to schedule the checkpointing automaticaly depends on the system
performance what we have discussed before( e.p. recovery speed,
current disk I/O situation).The only thing I will change on the
checkpointing process is to make it wirte out several pages and sleep
for a while if the system is busy, and then write several more,and so on.
2. Let me call it "Incremental checkpointing"(details please refer to the
former discussions).

Then I want do some test and comparison among:
  -- The current checkpointing mechanism
  -- The automatically scheduled checkpointing mechanism
  -- The incremental checkpointing mechanism
and we can know which one would be better.

I still have a questions about derby checkpointing. Someone can
help me to make it clear? ^_^.
I want to summarize what events will trigger a checkpoint?
On the derby website :
   http://db.apache.org/derby/papers/logformats.html
I found such comments:
-------------------------------------------------------------------------------------------------------------------------------------------
With the default values, a new log file is created (this is known as log 
switch) when a log file grows beyond 1MB and a checkpoint happens when the 
amount of log written is 10MB or more from the last checkpoint.

RawStore exposes a checkpoint method which clients can call, or a checkpoint 
is taken automatically by the RawStore when:

1. The log file grows beyond a certain size (configurable, default 1MB)
2. RawStore is shutdown and a checkpoint hasn't been done "for a while"
3. RawStore is recovered and a checkpoint hasn't been done "for a while"
-------------------------------------------------------------------------------------------------------------------------------------------
I am no very clear about what " for a while " means in the second and the 
third comments.
I also want to know is there any other events will trigger a checkpoint 
besides these?


Thanks.


Raymond

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