Motivation

When processing data, users want to have access to non-tabular (not stored in cache structures) data. 

Ignite provides a few options to set custom attributes on client side: per call (ServiceCallContext) and per connection (UserAttributes). Now there is no opportunity to set attributes on the "application level". Scenario is:

1. Application acquires Ignite connect from connection pool.
2. Application need specify ApplicationAttributesApplication attributes - an associative array specified on an application side. Business logic might depend on such attributes - application language, application name , date/time formats, debug tokensfor audit, etc ([2], [4]).SecuritySubject can be used to provide fine-grained access control to cache data. For example, CacheInterceptor saves the subject id it .
3. Another application re-uses this connect with own attributes values.

It's proposed to provide the opportunity to set attributes for application. Then there will be hierarchy of attributes:

1. Call level - ServiceCallContext
2. Application level - ApplicationAttributes
3. Connection level - UserAttributes, SecuritySubject

The access to the attributes must be provided for functions that are pre-created on Ignite cluster and aren't deployed by specific application. Examples:

• CacheInterceptor saves the SecuritySubject along with data and it can be used for

...

• fine-grained access control in QuerySqlFunction.
• Service extracts attribute from ServiceCallContext and, if absent, get default one from ApplicationAttributes.

It's proposed to introduce SessionContext API that is available from the functions and provides access to the attributes in order (call, application, connection).

Requirements:

1. The attributes ​​are set by application only once for Ignite API entry point (Ignite, IgniteClient, JDBC).
2. The attributes are available on all participating nodes of the application requests and queries.
3. The attributes must be accessible in pre-defined functions:
   1. QuerySqlFunction
   2. CacheInterceptor
   3. Service
   4. ComputeTask, ComputeJob

Attributes API that aren't part of the IEP:

1. ClientListenerConnectionContext#attributes - it's actually how client stores UserAttribute in connection context.
2. ComputeTaskSession#setAttribute - this mechanism is available only within Compute API. It allows attributes to be changed during task lifetime, use-case is different - send sync/async notifications between jobs about events happened during task lifetime.

Similar mechanisms in other DBMSs:

1. Application, Client contexts mechanisms exist in Oracle [1] and they are widely used [6].
2. Custom session variables exist in DBMS like

The requirements include:

1. Data must be accessible from user defined functions (QuerySqlFunction, CacheInterceptor) on all nodes participated in queries.
2. Application attributes ​​can change during the life of the connection (a connection from a connection pool can be sequentially used by different applications).

Ignite does not have a such API:

1. ServiceCallContext helps solve similar problems, but has several limitations - available only by calls via the IgniteService API and cannot be used for primitive operations.
2. UserAttributes - allows to set user attributes, but the attribute values ​​are fixed for the entire lifetime of the connection.
3. ClientListenerConnectionContext - it's available only on single node which directly accepts a client connection.

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1. SQLServer [8], Snowflake [7], MySQL [9]

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1. .

Description

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Setting application attributes

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Ignite 

1. Users set attributes with Ignite#withApplicationAttributes. It returns Ignite instance that is aware of the attributes.
2. Application attributes are propagated with all messages sent within operation on remote nodes (similar to GridIoSecurityAwareMessage)
3. ApplicationContext is an entrypoint for accessing all non-tabular data.
4. The access requires static methods, because objects injection isn't possible for user functions (QuerySqlFunction are static, CacheInterceptor is a cache singleton).
5. User can easily create own QuerySqlFunction  to get access to the attribute from SQL if needed.

/** ApplicationContext interface. It's an entrypoint for all non-tabular data. */
public class ApplicationContext {
    /** @returnExample Application attributes set for current thread. */
    public static @Nullable Map<String, String> getAttributes();

    /** @return Current SecuritySubject. */
	public static @Nullable SecuritySubject getSecuritySubject();
 }
 
/** Example, use it in QuerySqlFunction. */
public static class UserDefinedFunctions {
    /** @return Session ID set with application attributes. */
    @QuerySqlFunction
    public static @Nullable String sessionId(of usage.
try (Ignite ign = Ignition.start(ignCfg)) {
        Map<String, String> appAttrs = ApplicationContextF.getAttributes(asMap("SESSION_ID", "1234");
 
        return appAttrs == null ? null : appAttr.get("SESSION_ID");
    }	Ignite app = Ignite.withApplicationAttributes(appAttrs);	

 	...
}

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IgniteClient (Java)

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1. Users set attributes with IgniteClient#withApplicationAttributesClient should mirror the logic of Ignite node.
2. New feature is needed in the ClientBitmaskFeature protocol.

...

// Example of usage.
try (IgniteClient cln = Ignition.startClient(clnCfg)) {
    Map<String, String> appAttrs = F.asMap("SESSION_ID", "1234");

    try (ClientTransaction tx 	IgniteClient app = cln.transactions().withApplicationAttributes(appAttrs).txStart()) {
        ;	

 	...
    }
}

JDBC

The standard jdbc protocol describes the methods Connection#setClientInfo, which allow changing the values ​​of client attributes during the life of the connection [3]. Implementation features:

1. The list of attributes that can be set using #setClientInfo is arbitrary. The documentation recommends strictly limiting the set of attributes, but this is not necessary. For example, Oracle does not have such a limitation [5]. The setClientInfo array is completely translated into the getClientAttributes array ApplicationAttributes.
2. The parameters set in setClientInfo are passed along with each JdbcRequest (this requires a new feature in JdbcThinFeature).
3. The client must reset the set values ​​itself.

...

// JDBC connection to Ignite server.
try (Connection conn = DriverManager.getConnection(URL)) {
    conn.setClientInfo("SESSION_ID", "1234");
 
    ...
}

Spreading context across cluster nodes

1. Via the QueryStartRequest SQL message protocol (for jdbc, SQL transactions)
2. Via the transaction protocol for handling inserts (CacheInterceptor), since inserts are not always performed on the request initiator node.

Risks and Assumptions

// Describe project risks, such as API or binary compatibility issues, major protocol changes, etc.

1. It doesn't work for non-transactional ignite-node SQL but work for JDBC.

Discussion Links

Accessing attributes

SessionContext is an entrypoint for accessing attributes on all levels and other session-level data (e.g. SecurutySubject). Ignite provides SessionContextProviderResource to access to SessionContext.

1. Injecting the ProviderResource doesn't require new instance of CacheInterceptor or QuerySqlFunction target class for every call (every row or key).
2. Provider implementation is responsible for extracting SessionContext from Ignite thread.
3. Note, it proposes to make possible use non-static QuerySqlFunction to inject the resource.
   
   

/** SessionContext interface. It's an entrypoint for all attributes. */
public class SessionContext {
    /** @return Attribute by name. */
    public @Nullable String getAttribute(String attrName);

    /** @return Current SecuritySubject. */
	public @Nullable SecuritySubject getSecuritySubject();
 }
 
/** Example, use it in QuerySqlFunction. */
public static class UserDefinedFunctions {
    /** Injection performs once per query. */
    @SessionContextProviderResource
    public SessionContextProvider sesCtxProv;

    /** @return Session ID set with application attributes. */
    @QuerySqlFunction
    public @Nullable String sessionId() {             
		return sesCtxProv.getSessionContext().getAttribute("SESSION_ID");
    }
}

Risks and Assumptions

1. No security checks are performed on the application attributes.
2. Application attributes keys and values are strings, to avoid serialization problems.
3. User should specify only few application attributes, and they should be small.
4. UserAttributes currently fill with node attributes (~50 items on node start), and they are not transferred between nodes. This process should be changed.

Discussion Links

https://lists.apache.org/thread/c5j5yykr6tfrnp9zprhg9j69w63r11zx// Links to discussions on the devlist, if applicable.

Reference Links

[1] https://docs.oracle.com/en/database/oracle/oracle-database/19/dbseg/using-application-contexts-to-retrieve-user-information.html#GUID-51C9D5FA-6787-4F05-82EF-A5968BEDC5A0

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[9] https://dev.mysql.com/doc/refman/8.4/en/user-variables.html

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