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From "Raymond Raymond" <raymond_de...@hotmail.com>
Subject Re: Two questions on derby checkpointing
Date Thu, 16 Feb 2006 15:05:45 GMT
Suresh,thank you very much.

Raymond


>From: Suresh Thalamati <suresh.thalamati@gmail.com>
>Reply-To: <derby-dev@db.apache.org>
>To: derby-dev@db.apache.org
>Subject: Re: Two questions on derby checkpointing
>Date: Thu, 16 Feb 2006 01:11:48 -0800
>
>Raymond Raymond wrote:
>>I have some questions about derby checkpointing. Someone can
>>help me to make it clear? ^_^.
>>
>>1. 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"
>
>To my knowledge shutdown always does a checkpoint.
>
>
>>3. RawStore is recovered and a checkpoint hasn't been done "for a while"
>
>
>if there is an undo work or if we redo a log worth > 1000 bytes a
>checkpoint is requested.  See the check in LogToFile.java:recover() method 
>with following comment:
>
>// if we can figure out there there is very little in the
>// log (less than 1000 bytes),we haven't done any
>// rollbacks, then don't checkpoint. Otherwise checkpoint.
>
>
>
>>-------------------------------------------------------------------------------------------------------------------------------------------
>>
>>I am no very clear about what " for a while " means in the second and the 
>>third comments.
>>I also want to know are there any other events will trigger a checkpoint 
>>besides these?
>
>1) Online Backup will trigger a checkpoint
>2) Backup related calls freeze , unfreeze that allows users to backup a 
>dataabase using OS copy also will trigger a checkpoint.
>
>3) Inplace commress triggers a checkpoint when doing a truncate of the 
>table.
>
>That's all I can remeber offhand.
>
>
>
>>
>>
>>2. As what we discussed in the "incremental checkpointing issue" before,
>>I need to monitor the data reads and log writes, to gather some runtime
>>disk I/O information. So far, I found the basic classes to do data reads 
>>are :
>>org.apache.derby.impl.store.raw.data.RAFContainer.java
>>org.apache.derby.impl.store.raw.data.InputStreamContainer.java
>>
>>the basic class to do log writes is :
>>org.apache.derby.impl.store.raw.log.LogAccessFile.java
>>
>>Are there any other classes is involved in data reads and log writes 
>>directly?
>
>
>I also think those are the three classes make the actual I/O read/write 
>calls.
>
>
>hope that helps
>-suresh

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