The name is listed in a banner at the top of the page. It is not possible to change the target DB System if it was created from either of those locations. Note This process is for new imports, only.
If you are attempting to recover from a replication lag, see Replication Resynchronization. Channel Details View and manage your replication channels. OCID : the unique identifier of the Channel. Description : user-defined description of the channel Enabled : displays the status of the channel. Yes for enabled, No for disabled. State : displays the current lifecycle state of the channel.
Select the State Details tooltip to see more detail on the current state of the channel. Compartment : the compartment the channel was created in. Created : time and date the channel was created. Last Updated : time and date the channel was last updated. Port : the port number the source is communicating on. Username : the username of the replication user. SSL Mode : defines the security state of the connection to the source. The connection attempt fails if an encrypted connection cannot be established.
Displays the contents of the uploaded CA X certificate. Applier Username : the username of the replication applier. Checking the State of a Channel To check the status of a Channel:. This status is displayed for the following reasons: The Channel is not replicating due to an error.
The Details column on the Channels page lists why the channel needs attention. Pending actions are applied if the DB System is started. The Channel is being deleted. Enabling or Disabling a Channel Open the navigation menu and select Databases. Choose your Compartment. A list of Channels is displayed. The Channel's state changes to Updating and then to Inactive. The Channel's state changes to Updating and then to Active.
The following is assumed for this task: The channel is disabled. Reset is not possible on channels which are enabled.
The Channel status changes to Updating , then back to Inactive when the reset completes. Resuming a Channel Resuming a channel is used to start replication on a Channel which became inactive due to an error.
The Channel status changes to Updating , then to Active , if the error was corrected and the action is successful. To edit the channel:. Outbound Replication Outbound replication enables you to create asynchronous replicas of DB System databases. The following outbound replication scenarios are supported: DB System to external replica.
Note This replication scenario requires an additional network configuration to bridge the external network and the VCN to which the DB System is attached. Asynchronous replicas can be used for: Redistribution of data Disaster recovery Scale-out Custom point-in-time-recovery.
Note Outbound Replication is not managed functionality. If you require a longer value, you must create a new configuration with the required expiration value and create a new source DB System using the new configuration.
Asynchronous data replication occurs when an application updates a local replica of a table, stores replication information in a local queue, and then forwards the replication information to other replication sites at a later time. Consequently, asynchronous data replication is also called store-and-forward data replication. As Figure shows, Oracle uses its internal system of triggers, deferred transactions, deferred transaction queues, and job queues to propagate data-level changes asynchronously among master sites in an advanced replication system, as well as from an updatable snapshot to its master table.
With serial propagation , Oracle asynchronously propagates replicated transactions, one at a time, in the same order of commit as on the originating site. With parallel propagation , Oracle asynchronously propagates replicated transactions using multiple, parallel transit streams for higher throughput. When necessary, Oracle orders the execution of dependent transactions to ensure global database integrity. Parallel propagation uses the same execution mechanism that Oracle uses for parallel query, load, recovery, and other parallel operations.
Each server process propagates transactions through a single stream. A parallel coordinator process controls these server processes. The coordinator tracks transaction dependencies, allocates work to the server processes, and tracks their progress. After a site pushes a deferred transaction to its destination, the transaction remains in the deferred transaction queue until another job purges the applied transaction from the queue.
Updatable snapshots in an advanced replication environment can both "push" and "pull" data to and from its master table, respectively. Updates to an updatable snapshot are asynchronously pushed to its master table using Oracle's row-level, asynchronous data propagation mechanisms RPCs, deferred transactions, and job queues. Identical to basic replication environments, advanced replication systems use Oracle's snapshot refresh mechanism to pull changes asynchronously from a master table to associated updatable and read-only snapshots.
An updatable snapshot's push and pull tasks are independent operations that you can configure associatively or separately. For example, an advanced replication environment that consolidates information at a master site might configure updatable snapshots to push changes to the master site every hour but refresh updatable snapshots infrequently, if ever.
An Oracle symmetric replication environment requires several unique database user accounts to function properly, including replication administrators, propagators, and receivers. In most advanced replication configurations, just one account is used for all purposes - as a replication administrator, a replication propagator, and a replication receiver.
However, Oracle also supports distinct accounts for unique configurations. Advanced replication systems that support an update-anywhere model of data replicas must address the possibility of replication conflicts. The following sections explain the different types of replication conflicts, when they can occur, and how Oracle can detect and resolve replication conflicts.
Three types of conflicts can occur in an advanced replication environment: uniqueness conflicts, update conflicts, and delete conflicts. For example, consider what happens when two transactions that originate from two diffebent sites each insert a row into a respective table replica with the same primary key value - replication of the transactions will cause a uniqueness conflict. An update conflict happens when the replication of an update to a row conflicts with another update to the same row.
Update conflicts can happen when two different transactions, originating from different sites, update the same row at nearly the same time. A delete conflict happens when two transactions originate from different sites, with one transaction deleting a row that the other transaction updates or deletes. When designing applications that will work on top of a database system that uses advanced replication, you must consider the possibility of replication conflicts.
In doing so, applications must choose to employ one of several different replicated data ownership models that will ensure global database integrity by avoiding or resolving replication conflicts. Primary ownership , also called static ownership , is the replicated data model that basic read-only replication environments support. Primary ownership prevents all replication conflicts, because only a single server permits update access to a set of replicated data.
Rather than control the ownership of data at the table level, applications can employ horizontal and vertical partitioning to establish more granular static ownership of data. For example, applications might have update access to specific columns or rows in a replicated table on a site-by-site basis. The dynamic ownership replicated data model is less restrictive than primary site ownership. With dynamic ownership, the capability to update a data replica moves from site to site, still ensuring that only one site provides update access to specific data at any given point in time.
A workflow system clearly illustrates the concept of a dynamic ownership. For example, related departmental applications can read the status code of a product order to determine when they can and cannot update the order. Figure illustrates an application that uses a dynamic ownership model. Primary site ownership and dynamic ownership replication data models, which promote conflict avoidance, are often too restrictive or impossible to implement for some database applications.
Some applications must operate using a shared ownership replicated data model in which applications can update the data of any table replica at any time. When a shared data ownership system replicates changes asynchronously store-and-forward replication , corresponding applications must be sure to avoid, or detect and resolve replication conflicts if and when they occur.
For example:. When an application uses a shared ownership data model with asynchronous row-level replication, Oracle automatically detects uniqueness, update, and delete conflicts. To detect conflicts during replication, Oracle compares a minimal amount of row data from the originating site with the corresponding row information at the receiving site. When there are differences, Oracle detects the conflict.
To detect replication conflicts accurately, Oracle must be able to uniquely identify and match corresponding rows at different sites during data replication. Typically, Oracle's advanced replication facility uses the primary key of a table to uniquely identify rows in the table. When a table does not have a primary key, you must designate an alternate key - a column or set of columns that Oracle can use to identify rows in the table during data replication.
In either case, applications should not be allowed to update the identity columns of a table to ensure that Oracle can identify rows and preserve the integrity of replicated data. When a receiving site in an advanced replication system is using asynchronous row-level replication and it detects a conflict in a transaction, the default behavior is to log the conflict and the entire transaction, and leave the local version of the data intact.
In most cases, you should use Oracle's advanced replication facility to automate the resolution of replication conflicts. Oracle uses column groups to detect and resolve conflicts during asynchronous, row-level symmetric replication. A column group is a logical grouping of one or more columns in a table. Every column in a replicated table is part of a single column group.
When configuring replicated tables, you can create column groups and then assign columns and corresponding conflict resolution methods to each group.
Each column group in a replicated table can have a list of one or more conflict resolution methods. Indicating multiple conflict resolution methods for a group allows Oracle to resolve a conflict in different ways should others fail to resolve the conflict. When trying to resolve a conflict for a group, Oracle executes the group's resolution methods in the order that you list for the group. By default, every replicated table has a shadow column group.
A table's shadow column group contains all columns that are not within a specific column group. You cannot assign conflict resolution methods to a table's shadow group. When designing column groups you can choose from among many built-in conflict resolution methods. For example, to resolve update conflicts, you might choose to have Oracle overwrite the column values at the destination site with the column values from the originating site.
Oracle offers many other conflict resolution methods. Some applications have special requirements of an advanced replication system. The following sections explain the Oracle unique advanced replication options, including. Batch processing applications can change large amounts of data within a single transaction. In such cases, typical row-level replication could saturate a network with a huge quantity of data changes. To avoid such problems, a batch processing application that operates in an advanced replication environment can use Oracle's procedural replication to replicate simple stored procedure calls that will converge data replicas.
Procedural replication replicates only the call to a stored procedure that an application uses to update a table. Procedural replication does not replicate data modifications. To use procedural replication, at all sites you must replicate the packages that modify data in the system.
After replicating a package, you must generate a wrapper for this package at each site. When an application calls a packaged procedure at the local site to modify data, the wrapper ensures that the call is ultimately made to the same packaged procedure at all other sites in the replicated environment. Procedural replication can occur asynchronously or synchronously. When an advanced replication system replicates data using procedural replication, the procedures that replicate data are responsible for ensuring the integrity of the replicated data.
That is, you must design such procedures either to avoid or to detect replication conflicts and resolve them appropriately. Consequently, procedural replication is most typically used when databases are available only for the processing of large batch operations. In such situations, replication conflicts are unlikely because numerous transactions are not contending for the same data. Additional Information: See Oracle8 Replication.
Applications can update any replicated table at any site in a multimaster configuration. Oracle database servers operating as master sites in a multimaster environment automatically work to converge the data of all table replicas and to ensure global transaction consistency and data integrity. Asynchronous replication is the most common way to implement multimaster replication.
Other ways include synchronous replication and procedural replication, which are discussed later in this chapter. When you use asynchronous replication, an update of a table is stored in the deferred transaction queue at the master site where the change occurred. These changes are called deferred transactions. The deferred transactions are pushed or propagated to the other participating master sites at regular intervals.
You can control the amount of time in an interval. Using asynchronous replication means that conflicts are possible because the same row value might be updated at two different master sites at nearly the same time.
However, you can use techniques to avoid conflicts and, if conflicts occur, Oracle provides built-in mechanisms to resolve them. At times, you must stop all replication activity for a master group so that you can perform certain administrative tasks on the master group.
For example, you must stop all replication activity for a master group to issue data definition language DDL statements on any table in the group. Stopping all replication activity for a master group is called quiescing the group. When a master group is quiesced, users cannot perform data manipulation language DML statements on any of the objects in the master group. A snapshot contains a complete or partial copy of a target master table from a single point in time.
A snapshot may be read-only or updateable. Offload queries from the master site, because users can query the local snapshot instead. Increase data security by allowing you to replicate only a selected subset of the target master table's data set.
Read-Only Snapshots In a basic configuration, snapshots can provide read-only access to the table data that originates from a master site. Applications can query data from read-only snapshots to avoid network access regardless of network availability. However, applications throughout the system must access data at the master site to perform an update.
Figure illustrates basic, read-only replication. The master tables of read-only snapshots do not need to belong to a master group. Support complex snapshots. See Also: "Available Snapshots" for more information about complex snapshots. Figure Read-Only Snapshot Replication Updateable Snapshots In a more advanced configuration, you can create an updateable snapshot that allows users to insert, update, and delete rows of the target master table by performing these operations on the snapshot.
An updateable snapshot may also contain only a subset of the data in the target master table. Figure illustrates a replication environment using updateable snapshots.
Updateable snapshots are based on tables at a master site that have been set up to support replication. In fact, updateable snapshots must be part of a snapshot group that is based on a master group at a master site.
Updateable snapshots can be incrementally or "fast" refreshed. Oracle propagates the changes made to an updateable snapshot to the snapshot's remote master table. If necessary, the updates to the master table then cascade to all other master sites. Oracle can refresh an updateable snapshot as part of a refresh group in the same way it refreshes read-only snapshots. Updateable snapshots provide the following benefits:.
Require fewer resources than multimaster replication, while still supporting data updates. For example, because snapshots can reside on an Oracle8 i Lite database, the disk space and memory requirements for snapshot clients are much less than the requirements for an Oracle8 i server.
Snapshot Refresh To ensure that a snapshot is consistent with its master table, you need to refresh the snapshot periodically. Oracle provides the following three methods to refresh snapshots:. Complete refresh updates the entire snapshot. Force refresh performs a fast refresh when possible. When a fast refresh is not possible, force refresh performs a complete refresh.
When it is important for snapshots to be transactionally consistent with each other, you can organize them into refresh groups. By refreshing the refresh group, you can ensure that the data in all of the snapshots in the refresh group correspond to the same transactionally consistent point in time. A snapshot in a refresh group still can be refreshed individually, but doing so nullifies the benefits of the refresh group because refreshing the snapshot individually does not refresh the other snapshots in the refresh group.
A snapshot log is a table that records all of the DML changes to a master table. A snapshot log is associated with a single master table, and each master table has only one snapshot log, regardless of how many snapshots refresh from the master. A fast refresh of a snapshot is possible only if the snapshot's master table has a snapshot log.
When a snapshot is fast refreshed, entries in the snapshot's associated snapshot log that have appeared since the snapshot was last refreshed are applied to the snapshot. Deployment templates simplify the task of deploying and maintaining many remote snapshot sites.
Using deployment templates, you can define a collection of snapshot definitions at a master site, and you can use parameters in the definitions so that the snapshots can be customized for individual users or types of users.
For example, you might create one template for the sales force and another template for field service representatives. In this case, a parameter value might be the sales territory or the customer support level. When a remote user connects to a master site, the user can query a list of available templates. When the user instantiates a template, the appropriate snapshots are created and populated at the remote site. The appropriate parameter values can either be supplied by the remote user or taken from a table maintained at the master site.
Users can instantiate templates while connected to the master site over a network online instantiation , or while disconnected from the master site offline instantiation.
Offline instantiation is often used to decrease server loads during peak usage periods and to reduce remote connection times. To instantiate a template offline, you package the template and required data on some type of storage media, such as tape, CD-ROM, and so on. Then, instead of pulling the data from the master site, users pull the data from the storage media containing the template and data.
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