Searches until it finds a link specifying a database string. Then, you can access the remote database as follows: To access a remote schema object, you must be granted access to the remote object in the remote database. A database link connection allows local users to access data on a remote database. For example, if you connect to the hq database and access the dept table on this database as in Figure 28-2, you can issue the following: This query is direct because you are not accessing an object on a remote database. To achieve low latency and high availability, instances of these applications need to be deployed in datacenters that are close to their users. By using fixed user links, you can create non-global users whose password information is stored in unencrypted form in the LINK$ data dictionary table. For example, you can issue: This table describes how users access the remote database through the link: When connecting to the remote database, Oracle uses security information (userid/password) taken from the local session. A direct connection occurs when a client connects to a server and accesses information from a database contained on that server. Current user links are an aspect of the Oracle Advanced Security option. Oracle provides different ways for you to manage the users and privileges involved in a distributed system. The following table illustrates the possibilities: A shared database link can exist in any of these four configurations. The following table explains when Oracle completes the expansion of a partial global object name for views, synonyms, and program units: Does not expand partial global names--the data dictionary stores the exact text of the defining query. CREATE PUBLIC DATABASE LINK hq CONNECT TO jane IDENTIFIED BY doe USING 'hq'; "Specifying Link Users" to learn how to specify users where creating links. Fixed user links are easy to create and require low overhead because there are no SSL or directory requirements, but a security risk results from the storage of password information in the data dictionary. In short, if your application needs fast response time anywhere in the world, if it's required to be always online, and needs unlimited and elastic scalability of throughput and storage, you should build your application on Azure Cosmos DB. 99.999% read and write availability all around the world. Performance at scale Get relational databases … As one of the foundational services of Azure, Cosmos DB runs in every … Outline. AWS’s portfolio of purpose-built databases supports diverse data models and allows you to build use case driven, highly scalable, distributed applications. The fact that the username and password are stored in unencrypted form in the data dictionary creates a potential security weakness of fixed user database links. User called PUBLIC. The username and password are stored in unencrypted form in the data dictionary in the LINK$ table. She will have all scott's privileges if she connects locally and any audit records will be recorded as if she were scott. Guaranteed reads and writes served in less than 10 milliseconds at the 99th percentile. For example, this transaction updates the local database and the remote sales database: If all statements of a transaction reference only a single remote node, the transaction is remote, not distributed. Note that current user database links have these consequences: Create database links using the CREATE DATABASE LINK statement. The following steps occur (not necessarily in this exact order): Oracle Advanced Security Administrator's Guide for more information about enterprise user security. For example, if the global database name for hq is, and GLOBAL_NAMES is TRUE, then the link name must be called The userid/password is taken from the link definition rather than from the local session context. After the local Oracle database connects to the specified remote database on behalf of the local user that issued the SQL statement, object resolution continues as if the remote user had issued the associated SQL statement. When creating the link, you determine which user should connect to the remote database to access the data. These basic link types differ according to which users are allowed access to the remote database: User who created the link. A database link is a connection between two physical database servers that allows a client to access them as one logical database. These applications are typically deployed in multiple datacenters and are called globally distributed. 1.4.2. By using this API, you can carry out regular business continuity drills. An Oracle distributed database system has features that allow application developers and administrators to hide the physical location of database objects from applications and users. More than 128 million doses have been administered across 73 countries, according to data collected by Bloomberg. The Azure Cosmos DB replication protocol offers five well-defined, practical, and intuitive consistency models. The advantage of a connected user link is that a user referencing the link connects to the remote database as the same user. Create database links using the CREATE DATABASE LINK statement. Users connect using the username and password referenced in the link. Oracle Advanced Security Administrator's Guide for more information about these and other features of the Oracle Advanced Security option. While replication relies on distributed database technology, database replication offers applications benefits that are not possible within a pure distributed database environment. The default for the O7_DICTIONARY_ACCESSIBILITY initialization parameter is FALSE. To ensure that data has not been modified, deleted, or replayed during transmission, the security services of the Oracle Advanced Security option can generate a cryptographically secure message digest and include it with each packet sent across the network. The multi-region writes capability also enables: By using the Azure Cosmos DB multi-homing APIs, your application is aware of the nearest region and can send requests to that region. For example, A/P users can access the hq database as scott, but unlike fixed user links, scott's credentials are not stored where database users can see them. The Oracle database server accesses the non-Oracle system using Oracle Heterogeneous Services in conjunction with an agent. Consequently, the corresponding global database names are both changed as follows: In this case, the defining query of the employee_names view expands to a non-existent global database name. 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