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
