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From Jørgen Løland (JIRA) <j...@apache.org>
Subject [jira] Commented: (DERBY-3064) Implement the LogShipper that will enable the shipping of Log records from the master to the slave
Date Mon, 10 Sep 2007 12:37:29 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3064?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12526154

Jørgen Løland commented on DERBY-3064:

Thank you for addressing this issue, Narayanan. 

I had a look at the preliminary patch and have some questions.

1. I think "Factory" is used for object creation in cases where the object creation work is
hidden from the caller. This is the case for bootable services since the boot method does
this masking. In the log shipping case, however, I don't think "Factory" is a good name. Maybe
you could just call the interface (Replication)LogShipper?

2. The package names are very long. Since the package already contains "replication.master",
maybe we could shave off some characters in the class names? "Replication" could, e.g., be
removed. Just a thought.

3. Since you already have commented the variables, I think you should add another * (/* ->
/**) so that the comments become javadoc

4. I think the Daemon should be created by the MasterController since that class will be managing
everything on the master side

5. AsynchLogShipper does not need to know about the transmitter since Forced... does the log
shipping. The same goes for the log buffer.

6. How do you intend to create the log shipping service? I see that Forced... implements the
interface, but that the creator of Asynch... creates a Forced... object. In MasterController,
we would want to create an instance of the interface. Maybe Asynch could extend Forced? Again,
just a thought. With that design, all replication strategy specific methods like Forced#flushedInstance
could be made abstract, and adding other replication strategies (like 2-safe) later would
be really simple.

7. The javadoc for forceFlush is not describing the behavior of the method

8. I am concerned about the eternal loop in performWork. I guess this will be way too active,
especially in low workload cases. Also, control should be returned from the performWork method.
It should be up to the DaemonService to determine when it wants to ship log. A slight improvement
could be to let shipALogChunk returned the boolean return from LogBuffer#next, and change
performWork to look something like this:

performWork() {
   boolean sentSomething = true;
   while (sentSomething) {
      sentSomething = forcedLogShipper.shipALogChunk();

or even

performWork() {
   if (currentTimeMillis >= (timeOfLastLogShipment + shipmentWaitTime) {
      boolean sentSomething = true;
      while (sentSomething) {
         sentSomething = forcedLogShipper.shipALogChunk();

> Implement the LogShipper that will enable the shipping of Log records from the master
to the slave
> --------------------------------------------------------------------------------------------------
>                 Key: DERBY-3064
>                 URL: https://issues.apache.org/jira/browse/DERBY-3064
>             Project: Derby
>          Issue Type: Sub-task
>            Reporter: V.Narayanan
>         Attachments: LogShipperImpl_v1.diff, LogShipperImpl_v1.stat

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