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ScalarDB Cluster SQL gRPC API Guide

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This document describes the ScalarDB Cluster SQL gRPC API.

ScalarDB Cluster SQL provides a Java API that uses the gRPC API internally. If you use Java or a JVM language, you can use the Java API instead of the ScalarDB Cluster SQL gRPC API directly. For details about the Java API, see Developer Guide for ScalarDB Cluster with the Java API.

For details about the services and messages for the ScalarDB Cluster SQL gRPC API, see the definitions in the scalardb-cluster-sql.proto file. For ScalarDB Cluster users who have a commercial license, please contact support if you need the scalardb-cluster-sql.proto file.

ScalarDB Cluster SQL gRPC API is composed of the following services:

• scalardb.cluster.rpc.v1.sql.SqlTransaction: Provides a transaction capability for ScalarDB Cluster SQL.
• scalardb.cluster.rpc.v1.sql.SqlTwoPhaseCommitTransaction: Provides a two-phase commit transaction capability for ScalarDB Cluster SQL.
• scalardb.cluster.rpc.v1.sql.Metadata: Provides a metadata view of ScalarDB Cluster SQL.

The following sections describe how to use each service.

Overview of error handling in ScalarDB Cluster SQL gRPC API

Before describing how to use each service, this section explains how error handling works in ScalarDB Cluster SQL gRPC API.

ScalarDB Cluster SQL gRPC API employs Richer error model for error handling. This model enables servers to return and enables clients to consume additional error details expressed as one or more protobuf messages. ScalarDB Cluster SQL gRPC API uses google.rpc.ErrorInfo, which is one of the standard set of error message types, and puts additional error details in ErrorInfo fields.

ErrorInfo has the following fields:

• reason: A string that provides a short description of the error. The following sections describe the possible values of reason in each service.
• domain: A string that indicates the error's origin. In ScalarDB Cluster SQL gRPC API, this string is always set to com.scalar.db.cluster.sql.
• metadata: A map of metadata for the specific error. In ScalarDB Cluster SQL gRPC API, a transaction ID with the transactionId key in the map is put if the error is related to a transaction.

If you encounter an error, you can retrieve ErrorInfo from google.rpc.Status in the gRPC response, but the method for doing so depends on the programming language. Please refer to the appropriate documentation to understand how to get ErrorInfo in your specific programming language.

How to use the SqlTransaction service

The SqlTransaction service provides the following RPCs:

• Begin: Begins a transaction.
• Execute Executes a SQL statement.
• Commit: Commits a transaction.
• Rollback: Rolls back a transaction.

First, you call Begin to initiate a transaction. Following that, you can call Execute to read, write, and delete records. To finalize the transaction, call Commit. Alternatively, you can call Rollback at any time before the transaction is committed to cancel it. By calling Begin, you receive a transaction ID in the response, which you can then use to call Execute, Commit, and Rollback.

Also, you can call Execute without a transaction ID to execute a one-shot transaction. In this case, the transaction is automatically committed after it is executed. You can use this method to execute DDL statements as well. For details on the supported SQL statements, refer to ScalarDB SQL Grammar. Please note, however, that Execute supports only DML and DDL statements.

When you call Begin, you can optionally specify a transaction ID. If you specify a transaction ID, the user is responsible for guaranteeing the uniqueness of the ID. If you do not specify a transaction ID, ScalarDB Cluster will generate a transaction ID for the transaction.

You need to set RequestHeader for each RPC request. RequestHeader contains a hop_limit field, which restricts the number of hops for a request. The purpose of the hop_limit is to prevent infinite loops within the cluster. Each time a request is forwarded to another cluster node, the hop_limit decreases by one. If the hop_limit reaches zero, the request will be rejected.

Error handling

The table below shows the status code and the possible values of reason in ErrorInfo in each RPC in the SqlTransaction service:

RPC	Status code	reason in ErrorInfo	Description
Begin	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Begin	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Begin	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Begin	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Execute	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Execute	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Execute	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. This error indicates that the transaction has expired or the routing information has been updated due to cluster topology changes. In this case, please retry the transaction from the beginning.
Execute	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Execute	FAILED_PRECONDITION	TRANSACTION_CONFLICT	A transaction conflict occurred. If you encounter this error, please retry the transaction from the beginning.
Execute	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Commit	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Commit	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Commit	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. This error indicates that the transaction has expired or the routing information has been updated due to cluster topology changes. In this case, please retry the transaction from the beginning.
Commit	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Commit	FAILED_PRECONDITION	TRANSACTION_CONFLICT	A transaction conflict occurred. If you encounter this error, please retry the transaction from the beginning.
Commit	INTERNAL	UNKNOWN_TRANSACTION_STATUS	The status of the transaction is unknown (it is uncertain whether the transaction was successfully committed or not). In this situation, you need to check whether the transaction was successfully committed, and if not, to retry it. The responsibility for determining the transaction status rests with the users. It may be beneficial to create a transaction status table and update it in conjunction with other application data so that you can determine the status of a transaction from the table itself.
Commit	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Rollback	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Rollback	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Rollback	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. In case of a rollback, you do not need to retry the transaction because the transaction will expire automatically.
Rollback	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. In case of a rollback, you do not need to retry the transaction because the transaction will expire automatically.
Rollback	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.

If you encounter an error, you should roll back the transaction, except in the case of Begin. Then, you can retry the transaction from the beginning for the errors that can be resolved by retrying.

Besides the errors listed above, you may encounter errors returned by the gRPC library. In these cases, the response will not contain ErrorInfo. For details, refer to the gRPC documentation.

You can set a deadline for each RPC in gRPC. If the deadline is exceeded, you will receive a DEADLINE_EXCEEDED error. In general, you should roll back the transaction in this situation, unless the RPC is Begin or Commit. In the case of Commit, the situation is equivalent to UNKNOWN_TRANSACTION_STATUS (it is uncertain whether the transaction was successfully committed or not), and you must handle the error in the same way.

How to use the SqlTwoPhaseCommitTransaction service

The SqlTwoPhaseCommitTransaction service provides the following RPCs:

• Begin: Begins a transaction.
• Join: Joins a transaction.
• Execute Executes a SQL statement.
• Prepare: Prepares a transaction.
• Validate: Validates a transaction.
• Commit: Commits a transaction.
• Rollback: Rolls back a transaction.

First, you call Begin to initiate a transaction if you are the coordinator process. Alternatively, if you are a participant process, you can call Join to take part in a transaction that the coordinator has already begun. Following that, you can call Execute to read, write, and delete records. To finalize the transaction, call Prepare, Validate, and then Commit in order. Alternatively, you can call Rollback at any time before the transaction is committed to cancel it. By calling Begin or Join, you receive a transaction ID in the response, which you can then use to call Execute, Prepare, Validate, Commit, and Rollback.

In addition, you can call Execute without a transaction ID to execute a one-shot transaction. In this case, the transaction is automatically committed after it is executed. You can use this method to execute DDL statements as well. For details on the supported SQL statements, refer to ScalarDB SQL Grammar. Please note, however, that Execute supports only DML and DDL statements.

When you call Begin, you can optionally specify a transaction ID. If you specify a transaction ID, the user is responsible for guaranteeing the uniqueness of the ID. If you do not specify a transaction ID, ScalarDB Cluster will generate a transaction ID for the transaction.

You need to set RequestHeader for each RPC request. RequestHeader contains a hop_limit field, which restricts the number of hops for a request. The purpose of the hop_limit is to prevent infinite loops within the cluster. Each time a request is forwarded to another cluster node, the hop_limit decreases by one. If the hop_limit reaches zero, the request will be rejected.

Error handling

The table below shows the status code and the possible values of reason in ErrorInfo in each RPC in the SqlTwoPhaseCommitTransaction service:

RPC	Status code	reason in ErrorInfo	Description
Begin, Join	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Begin, Join	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Begin, Join	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Begin, Join	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Execute	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Execute	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Execute	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. This error indicates that the transaction has expired or the routing information has been updated due to cluster topology changes. In this case, please retry the transaction from the beginning.
Execute	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Execute	FAILED_PRECONDITION	TRANSACTION_CONFLICT	A transaction conflict occurred. If you encounter this error, please retry the transaction from the beginning.
Execute	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Prepare, Validate	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Prepare, Validate	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Prepare, Validate	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. This error indicates that the transaction has expired or the routing information has been updated due to cluster topology changes. In this case, please retry the transaction from the beginning.
Prepare, Validate	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Prepare, Validate	FAILED_PRECONDITION	TRANSACTION_CONFLICT	A transaction conflict occurred. If you encounter this error, please retry the transaction from the beginning.
Prepare, Validate	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Commit	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Commit	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Commit	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. This error indicates that the transaction has expired or the routing information has been updated due to cluster topology changes. In this case, please retry the transaction from the beginning.
Commit	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. This occurs when the routing information between cluster nodes is inconsistent. The error is usually resolved in a short amount of time, so you can retry the transaction from the beginning after some time has passed since encountering this error.
Commit	FAILED_PRECONDITION	TRANSACTION_CONFLICT	A transaction conflict occurred. If you encounter this error, please retry the transaction from the beginning.
Commit	INTERNAL	UNKNOWN_TRANSACTION_STATUS	The status of the transaction is unknown (it is uncertain whether the transaction was successfully committed or not). In this situation, you need to check whether the transaction was successfully committed, and if not, to retry it. The responsibility for determining the transaction status rests with the users. It may be beneficial to create a transaction status table and update it in conjunction with other application data so that you can determine the status of a transaction from the table itself.
Commit	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.
Rollback	INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
Rollback	FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
Rollback	NOT_FOUND	TRANSACTION_NOT_FOUND	The transaction associated with the specified transaction ID was not found. In case of a rollback, you do not need to retry the transaction because the transaction will expire automatically.
Rollback	INTERNAL	HOP_LIMIT_EXCEEDED	The hop limit was exceeded. In case of a rollback, you do not need to retry the transaction because the transaction will expire automatically.
Rollback	INTERNAL	INTERNAL_ERROR	The operation has failed due to transient or nontransient faults. You can try retrying the transaction from the beginning, but the transaction may still fail if the cause is nontransient.

If you encounter an error, you should roll back the transaction, except in the case of Begin or Join. Then, you can retry the transaction from the beginning for the errors that can be resolved by retrying.

Besides the errors listed above, you may encounter errors returned by the gRPC library. In these cases, the response will not contain ErrorInfo. For details, refer to the gRPC documentation.

You can set a deadline for each RPC in gRPC. If the deadline is exceeded, you will receive a DEADLINE_EXCEEDED error. In general, you should roll back the transaction in this situation, unless the RPC is Begin, Join, or Commit. In the case of Commit, the situation is equivalent to UNKNOWN_TRANSACTION_STATUS (it is uncertain whether the transaction was successfully committed or not), and you must handle the error in the same way.

How to use the Metadata service

The Metadata service provides the following RPCs:

• GetNamespaceMetadata: Retrieves namespace metadata of the specified namespace.
• ListTableMetadataInNamespace: Retrieves table metadata of tables in the specified namespace.
• GetTableMetadata: Retrieves table metadata of the specified table.

Error handling

The table below shows the status code and the possible values of reason in ErrorInfo for all RPCs in the Metadata service:

Status code	reason in ErrorInfo	Description
INVALID_ARGUMENT	ILLEGAL_ARGUMENT	The argument in the request message is invalid.
FAILED_PRECONDITION	ILLEGAL_STATE	The RPC was called in an invalid state.
INTERNAL	INTERNAL_ERROR	The operation has failed.

Besides the errors listed above, you may encounter errors returned by the gRPC library. In these cases, the response will not contain ErrorInfo. For details, refer to the gRPC documentation.