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===========================================
MySQL Replication Servers
Lars Thalmann and Johan Andersson
2003 MySQL AB
===========================================
-------------------------------------------------------------------------------
PRIMARY SYSTEM STANDBY SYSTEM
REPLICATION SERVER REPLICATION SERVER
(PS or SOURCE SYSTEM) (SS or DESTINATION SYSTEM)
+------------------+ +-------------------------+
| RepMain | | RepMain [Requests] |
| | +-------------------------+
| | | Requestor [Executes] |
+------------------+ +-------------------------+
PS --- | ExtNDB | TransPS | --- | TransSS | AppNDB | --- SS
+------------------+ +-------------------------+
(GCIContainer) (GCIContainer)
(RepState)
Figure 1: Replication Server Threads
Component List
--------------
RepMain
Main thread that runs command-line interpreter [Requests]
Requestor
Thread that runs RepState::execute [Executes]
ExtNDB
Extracts transaction epochs from NDB Cluster
TransPS, TransSS
Transfers information (control and epoch buffers) between
Replication Servers.
AppNDB
Applies transaction epochs to NDB Cluster
-------------------------------------------------------------------------------
RepState Control
Object
+------------------+
| RepState |
| [Requests] |
| [Executes] |
+------------------+
| RepStateRequest | --- ExtSender
+------------------+
Figure 2: RepState Object
The RepState object is shared by all components.
-------------------------------------------------------------------------------
Dependent Directories
---------------------
rep/adapters Appliers and Extractors
All code dependent on the database system
rep/transfer
Depends on NDB transporters
rep/state
Shared resources for all components
Independent Directories
-----------------------
rep/storage Storage of epochs
Should not depend on any transporters/NDB specific
rep/repstate
Should only have a reference to an ExtSender for the external PS REP node
-------------------------------------------------------------------------------
Replication Teminology
----------------------
GLOBAL CHECKPOINT <global checkpoint id - gci>
A global checkpoint is a point in time when all database server
are synchronized.
NODE
A database server with information.
NODE GROUP <node group id>
A set of database servers, all storing the same information.
SUBSCRIPTION <subscription id>.
A "subscription" is a collection of services that a source system
provides. The main to services belonging to a subscription are
"log" and "scan". Log provides the replication servers with
log entries (epochs) and scan provides the replication servers
with scanned data (also stored in epochs).
EPOCH <subscription id, gci>
An "epoch" is a log of all database changes between two time points.
(An epoch can have redundant log entries.) An epoch is named by the
number of the time slice between the two time points.
EPOCH BUFFER <subscription id, gci, node group id>
An "epoch buffer" is a part of the log belonging to an epoch. An
epoch buffer does not contain any redundancy.
Two epoch buffers with the same subscription id and gci can be
"complements" or "duplicates" to each other. If they are complements,
they store different information, if they are duplicates then they
store equivalent information (the information need not be identical,
but it is equivalent for the purpose of restoring the original
information). If they are duplicates then they have the same name,
i.e. same subscription id, gci, and node group id.
CHANNEL <subscription id>
A "channel" is a collection of epoch buffers belonging to
a specific subscription. (The channel can exist before it is
assigned to a subscription.)
SUBSCRIPTION CONSISTENT
A database is "subscription consistent" or "consistent with respect
to a subscription" if ...
Architectural Terminology
-------------------------
ADAPTER
An "adapter" is either an applier or an extractor.
APPLIER
An "applier" is a a collection of threads in the replication server
that applies epochs to a destination database system.
EXTRACTOR
An "extractor" is a collection of theads in the replication server
that receives epochs from a source database system.
TRANSFER COMPONENT
A "transfer component" is a thread in the replication server that is
responsible for the connection with another replication server.
REQUESTOR
A thread in the replication server that controls replication.
|
