Simplify initiation of replication
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Key: DERBY-4197
URL: https://issues.apache.org/jira/browse/DERBY-4197
Project: Derby
Issue Type: New Feature
Components: Replication
Affects Versions: 10.6.0.0
Reporter: Jørgen Løland
Priority: Minor
Starting Derby replication is brittle; you need to perform multiple steps in
exact order. Furthermore, the steps involves freezing the database on the
master Derby instance the time it takes to copy the database to the slave node.
A much simpler way to start replication would be:
1) Make an online backup of the database on the master Derby instance. Enable
log archiving.
2) Copy the backup to the slave node while the master Derby instance continues
to handle transactions
3) Boot the slave database in slave mode.
4) Master sends all log written since the backup was made, or from a specified
log instant (a number that can be specified as an option to either the
startSlave or startMaster command?).
The main implementation effort is in step 4, because this step requires the
master derby instance to read and send log records that are on disk. This
differs from the current replication code that captures log records on the
master as they are about to be written to disk (i.e., replication does not read
files).
Since the master instance is supposed to continue transaction processing, it
will write to the latest log file while the replication thread will have to
read log files (including the currently open one). The Derby code that reads
log files is written to handle a single thread (the recovery thread) only in
the current implementation.
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