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Date: Thu, 12 Jul 2007 01:57:04 -0700 (PDT)
From: =?utf-8?Q?J=C3=B8rgen_L=C3=B8land_=28JIRA=29?= <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-2926) Replication: Add a log buffer for
 log records that should be shipped to the slave
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    [ https://issues.apache.org/jira/browse/DERBY-2926?page=3Dcom.atlassian=
.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12512012 ]=20

J=C3=B8rgen L=C3=B8land commented on DERBY-2926:
--------------------------------------

Note the questions below...

PLAN:
I am planing to write the buffer as a linked list of ReplicationLogRecord o=
bjects, each containing the same information that is passed to LogToFile.ap=
pendLogRecord:

byte[] data
int offset
int length
byte[] optionaldata
int optionalDataOffset
int optionalDataLength

This is the same information that is sent in DERBY-2872 using RMI calls. Lo=
g records will be appended to the buffer somewhere in the LogFactory, while=
 a log shipping service will remove log records from it. Adding and removin=
g log records from the buffer is not part of this jira.

QUESTIONS:
* It will be very easy to recycle the ReplicationLogRecord objects that mak=
e up the linked list. Once the log-information in an object has been shippe=
d to the slave, the object could be put in a pool of recycled objects. This=
 would significantly reduce the number of ReplicationLogRecord objects that=
 must be created and garbage collected, but may increase the memory usage s=
ince the objects in the pool are not removed from memory. *Is recycling con=
sidered good or bad practice?*

* Will it be ok to create a new directory for this, e.g. java/engine/org/ap=
ache/derby/impl/store/replication/buffer/ ? It is likely that more replicat=
ion functionality will be added to store later, and /store/replication coul=
d then be used for all of this.


> Replication: Add a log buffer for log records that should be shipped to t=
he slave
> -------------------------------------------------------------------------=
--------
>
>                 Key: DERBY-2926
>                 URL: https://issues.apache.org/jira/browse/DERBY-2926
>             Project: Derby
>          Issue Type: Sub-task
>          Components: Store
>    Affects Versions: 10.4.0.0
>            Reporter: J=C3=B8rgen L=C3=B8land
>            Assignee: J=C3=B8rgen L=C3=B8land
>
> When a Derby instance has the master role for a database, log records are=
 shipped to the slave to keep it up to date. A buffer is needed because the=
 log records should not be shipped one at a time. Also, writing the log rec=
ords to a buffer instead of sending them immediately removes the network co=
mmunication from the critical path for the transaction.

--=20
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