~drizzle-trunk/drizzle/development

package drizzled.message;
option optimize_for = SPEED;

import "table.proto";
import "schema.proto";

/*
 * @file
 *
 * This file contains definitions for protobuffer messages that
 * are involved in Drizzle's replication system.
 *
 * @note
 *
 * We do not discuss implementation specifics about how messages
 * are transmitted across the wire in this documentation because a
 * discussion about those implementation details is immaterial to the
 * definition of the messages used in replication.
 *
 * For a discussion on the implementation of how messages are transmitted
 * to replicas, see the plugins which implement the replication system.
 *
 * @details
 *
 * Messages defined in this file are related in the following ways:
 *
 * ------------------------------------------------------------------
 * |                                                                |
 * | Transaction message                                            |
 * |                                                                |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | TransactionContext message                              |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Statement message 1                                     |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Statement message 2                                     |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * |                             ...                                |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Statement message N                                     |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * ------------------------------------------------------------------
 *
 * with each Statement message looking like so:
 *
 * ------------------------------------------------------------------
 * |                                                                |
 * | Statement message                                              |
 * |                                                                |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Common information                                      |  |
 * |   |                                                         |  |
 * |   |  - Type of Statement (INSERT, DELETE, etc)              |  |
 * |   |  - Start Timestamp                                      |  |
 * |   |  - End Timestamp                                        |  |
 * |   |  - (OPTIONAL) Actual SQL query string                   |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Statement subclass message 1 (see below)                |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * |                             ...                                |
 * |   -----------------------------------------------------------  |
 * |   |                                                         |  |
 * |   | Statement subclass message N (see below)                |  |
 * |   |                                                         |  |
 * |   -----------------------------------------------------------  |
 * ------------------------------------------------------------------
 *
 * The Transaction Message
 * =======================
 *
 * The main "envelope" message which represents an atomic transaction
 * which changed the state of a server is the Transaction message class.
 *
 * The Transaction message contains two pieces:
 *
 *   1) A TransactionContext message containing information about the
 *      transaction as a whole, such as the ID of the executing server, 
 *      the start and end timestamp of the transaction, and a globally-
 *      unique identifier for the transaction.
 *
 *   2) A vector of Statement messages representing the distinct SQL
 *      statements which modified the state of the server.  The Statement
 *      message is, itself, a generic envelope message containing a
 *      sub-message which describes the specific data modification which
 *      occurred on the server (such as, for instance, an INSERT statement.
 *
 * The Statement Message
 * =====================
 *
 * The generic "envelope" message containing information common to each
 * SQL statement executed against a server (such as a start and end timestamp
 * and the type of the SQL statement) as well as a Statement subclass message
 * describing the specific data modification event on the server.
 *
 * Each Statement message contains a type member which indicates how readers
 * of the Statement should construct the inner Statement subclass representing
 * a data change.
 *
 * For example, suppose we have have read a Transaction message and have executed
 * the following code:
 *
 * @code
 *
 * message::Statement &statement= transaction.statement(0); // Get first statement
 * 
 * switch (statement.type())
 * {
 *   case Statement::INSERT:
 *   {
 *     // Assume this is where we land...so, we know that the Statement
 *     // message represents an INSERT SQL statement.  We must now get the
 *     // specific information describing the INSERT statement.
 *     //
 *     // We assume here a simple INSERT statement that does not represent
 *     // a bulk operation.
 *     message::InsertHeader &insert_header= statement.insert_header();
 *     message::TableMetadata &table_metadata= insert_header.table_metadata();
 *     
 *     // Grab table name and echo out as start of INSERT SQL string...
 *     cout << "INSERT INTO `" << table_metadata.schema_name();
 *     cout << "`.`" << table_metadata.table_name() << "` (";
 *
 *     // Add field list to SQL string...
 *     uint32_t num_fields= insert_header.field_metadata_size();
 *     uint32_t x, y;
 *
 *     for (x= 0; x < num_fields; ++x)
 *     {
 *       message::FieldMetadata &field_metadata= insert_header.field_metadata(x);
 *       if (x != 0)
 *         cout << ',';
 *       cout << "`" << field_metadata.name() << "`";
 *     }
 *
 *     cout << ") VALUES (";
 *
 *     // Add insert values
 *     message::InsertData &insert_data= statement.insert_data();
 *     uint32_t num_records= insert_data.record_size();
 *     
 *     for (x= 0; x < num_records; ++x)
 *     {
 *       if (x != 0)
 *         cout << "),(";
 *       for (y= 0; y < num_fields; ++y)
 *       {
 *         if (y != 0)
 *           cout << ',';
 *         cout << "'" << insert_data.record(x).insert_value(y) << "'";
 *       }
 *     }
 *     cout << ")";
 *   }
 *   ...
 * }
 *
 * @endcode
 * 
 * How Bulk Operations Work
 * ========================
 *
 * Certain operations which change large volumes of data on a server
 * present a specific set of problems for a transaction coordinator or
 * replication service. If all operations must complete atomically on a
 * publishing server before replicas are delivered the complete
 * transactional unit:
 *
 * 1) The publishing server could consume a large amount of memory
 *    building an in-memory Transaction message containing all the
 *    operations contained  in the entire transaction.
 * 
 * 2) A replica, or subscribing server, is wasting time waiting on the
 *    eventual completion (commit) of the large transaction on the
 *    publishing server. It could be applying pieces of the large
 *    transaction in the meantime...
 *
 * In order to prevent the problems inherent in 1) and 2) above, Drizzle's 
 * replication system uses a mechanism which provides bulk change
 * operations.
 *
 * When a regular SQL statement modifies or inserts more rows than a
 * certain threshold, Drizzle's replication services component will begin
 * sending Transaction messages to replicas which contain a chunk
 * (or "segment") of the data which has been changed on the publisher.
 *
 * When data is inserted, updated, or modified in the database, a
 * header containing information about modified tables and fields is 
 * matched with one or more data segments which contain the actual
 * values changed in the statement.
 *
 * It's easiest to understand this mechanism by following through a real-world
 * scenario.
 *
 * Suppose the following table:
 *
 * CREATE TABLE test.person
 * (
 *   id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
 * , first_name VARCHAR(50)
 * , last_name VARCHAR(50)
 * , is_active CHAR(1) NOT NULL DEFAULT 'Y'
 * );
 *
 * Also suppose that test.t1 contains <strong>1 million records</strong>.
 *
 * Next, suppose a client issues the SQL statement:
 *
 * UPDATE test.person SET is_active = 'N';
 * 
 * It is clear that one million records could be updated by this statement 
 * (we say, "could be" since Drizzle does not actually update a record if 
 * the UPDATE would not change the existing record...).
 *
 * In order to prevent the publishing server from having to construct an 
 * enormous Transaction message, Drizzle's replication services component 
 * will do the following:
 *
 * 1) Construct a Transaction message with a transaction context containing
 *    information about the originating server, the transaction ID, and 
 *    timestamp information.
 *
 * 2) Construct an UpdateHeader message with information about the tables
 *    and fields involved in the UPDATE statement.  Push this UpdateHeader
 *    message onto the Transaction message's statement vector.
 *
 * 3) Construct an UpdateData message.  Set the segment_id member to 1.
 *    Set the end_segment member to true.
 *
 * 4) For every record updated in a storage engine, the ReplicationServices
 *    component builds a new UpdateRecord message and appends this message
 *    to the aforementioned UpdateData message's record vector.
 *
 * 5) After a certain threshold of records is reached, the
 *    ReplicationServices component sets the current UpdateData message's
 *    end_segment member to false, and proceeds to send the Transaction
 *    message to replicators.
 *
 * 6) The ReplicationServices component then constructs a new Transaction
 *    message and constructs a transaction context with the same
 *    transaction ID and server information.
 *
 * 7) A new UpdateData message is created.  The message's segment_id is 
 *    set to N+1 and as new records are updated, new UpdateRecord messages
 *    are appended to the UpdateData message's record vector.
 *
 * 8) While records are being updated, we repeat steps 5 through 7, with 
 *    only the final UpdateData message having its end_segment member set
 *    to true.
 *
 * Handling ROLLBACKs
 * ==================
 *
 * Any time a transaction is rolled back, a single Transaction message is
 * containing a Statement with type = ROLLBACK is sent to replicators.  
 *
 * What the replicator does with this information depends on the
 * replicator.  For most, only rollbacks of bulk operations will actually
 * trigger any real action on a replica, since non-bulk operations won't
 * have changed any data on a replica and the ROLLBACK is only sent to a 
 * replica to notify it of a transaction being rolled back (so that the 
 * replica can understand transaction ID sequence gaps...)
 */

/*
 * Some minimal information transferred in the header of Statement
 * submessage classes which identifies metadata about a specific
 * field involved in a Statemet.
 */
message FieldMetadata
{
  required Table.Field.FieldType type = 1; /* Type of the field */
  required string name = 2; /* Name of the field */
}

/*
 * Minimal information transferred in the header of Statement submessage
 * classes which identifies metadata about the schema objects being
 * modified in a Statement.
 */
message TableMetadata
{
  required string schema_name = 1; /* Name of the containing schema */
  required string table_name = 2; /* Name of the table */
}

/*
  Context for a transaction.
*/
message TransactionContext
{
  required uint32 server_id = 1; /* Unique identifier of a server */
  required uint64 transaction_id = 2; /* Globally-unique transaction ID */
  required uint64 start_timestamp = 3; /* Timestamp of when the transaction started */
  required uint64 end_timestamp = 4; /* Timestamp of when the transaction ended */
}

/*
 * Represents a single record being inserted into a single table.
 *
 * @note 
 *
 * An INSERT Statement contains one or more InsertRecord submessages, each
 * of which represents a single record being inserted into a table.
 */
message InsertRecord
{
  repeated bytes insert_value = 1;
  repeated bool is_null = 2;
}

/*
 * Represents statements which insert data into the database:
 *
 * INSERT
 * INSERT SELECT
 * LOAD DATA INFILE
 * REPLACE (is a delete and an insert)
 *
 * The statement is composed of a header (InsertHeader) containing
 * metadata about affected tables and fields, as well as one or more data
 * segments (InsertData) containing the actual records
 * being inserted.
 *
 * @note
 *
 * Bulk insert operations will have >1 data segment, with the last data
 * segment having its end_segment member set to true.
 */
message InsertHeader
{
  required TableMetadata table_metadata = 1; /* Minimal metadata about the table affected */
  repeated FieldMetadata field_metadata = 2; /* Collection of metadata about fields affected */
}

message InsertData
{
  required uint32 segment_id = 1; /* The segment number */
  required bool end_segment = 2; /* Is this the final segment? */
  repeated InsertRecord record = 3; /* The records inserted */
}

/*
 * Represents a single record being updated in a single table.
 *
 * @note 
 *
 * An UPDATE Statement contains one or more UpdateRecord submessages, each
 * of which represents a single record being updated in a table.
 */
message UpdateRecord
{
  repeated bytes key_value = 1; /* The value of keys of updated records (unique or primary key) */
  repeated bytes after_value = 2; /* The value of the field after the update */
  repeated bytes before_value = 3; /* The value of the field before the update (optional) */
  repeated bool is_null = 4;
}

/*
 * Represents statements which update data in the database:
 *
 * INSERT ... ON DUPLICATE KEY UPDATE
 * UPDATE
 * REPLACE INTO when the UPDATE optimization occurs.
 *
 * The statement is composed of a header (UpdateHeader) containing
 * metadata about affected tables and fields, as well as one or more data
 * segments (UpdateData) containing the actual records
 * being updateed.
 *
 * @note
 *
 * Bulk update operations will have >1 data segment, with the last data
 * segment having its end_segment member set to true.
 */
message UpdateHeader
{
  required TableMetadata table_metadata = 1; /* Minimal metadata about the table affected */
  repeated FieldMetadata key_field_metadata = 2; /* Collection of metadata about key fields */
  repeated FieldMetadata set_field_metadata = 3; /* Collection of metadata about fields affected */
}

message UpdateData
{
  required uint32 segment_id = 1; /* The segment number */
  required bool end_segment = 2; /* Is this the final segment? */
  repeated UpdateRecord record = 3; /* Collection of same size as above metadata containing the
                                       values of all records of all the fields being updated. */
}

/*
 * Represents a single record being deleted in a single table.
 *
 * @note 
 *
 * A DELETE Statement contains one or more DeleteRecord submessages, each
 * of which represents a single record being delete from a table.
 */
message DeleteRecord
{
  repeated bytes key_value = 1;
}

/*
 * Represents statements which delete data from the database:
 *
 * DELETE
 * REPLACE (is a delete and an insert)
 *
 * The statement is composed of a header (DeleteHeader) containing
 * metadata about affected tables and fields, as well as one or more data
 * segments (DeleteData) containing the actual records
 * being deleteed.
 *
 * @note
 *
 * Bulk delete operations will have >1 data segment, with the last data
 * segment having its end_segment member set to true.
 */
message DeleteHeader
{
  required TableMetadata table_metadata = 1; /* Minimal metadata about the table affected */
  repeated FieldMetadata key_field_metadata = 2; /* Collection of metadata about key fields */
}

message DeleteData
{
  required uint32 segment_id = 1; /* The segment number */
  required bool end_segment = 2; /* Is this the final segment? */
  repeated DeleteRecord record = 3; /* Collection of same size as above metadata containing the
                                       values of all records of all the fields being deleted. */
}

/*
 * Represents a TRUNCATE TABLE statement
 */
message TruncateTableStatement
{
  required TableMetadata table_metadata = 1; /* Metadata about table to truncate */
}

/*
 * Represents a CREATE SCHEMA statement
 */
message CreateSchemaStatement
{
  required Schema schema = 1; /* Definition of new schema */
}

/*
 * Represents an ALTER SCHEMA statement
 */
message AlterSchemaStatement
{
  required Schema before = 1; /* Definition of old schema */
  required Schema after = 2; /* Definition of new schema */
}

/*
 * Represents a DROP SCHEMA statement
 */
message DropSchemaStatement
{
  required string schema_name = 1; /* Name of the schema to drop */
}

/*
 * Represents a CREATE TABLE statement.
 */
message CreateTableStatement
{
  required Table table = 1; /* The full table definition for the new table */
}

/*
 * Represents an ALTER TABLE statement.
 */
message AlterTableStatement
{
  required Table before = 1; /* The prior full table definition */
  required Table after = 2; /* The new full table definition */
}

/*
 * Represents a DROP TABLE statement
 */
message DropTableStatement
{
  required TableMetadata table_metadata = 1; /* Minimal metadata about the table to be dropped */
  optional bool if_exists_clause = 2; /* Did the user specify an IF EXISTS clause? */
}

/*
 * Represents a SET statement
 *
 * @note
 *
 * This is constructed only for changes in a global variable.  For changes
 * to a session-local variable, the variable's contents are not transmitted
 * as Statement messages.
 */
message SetVariableStatement
{
  required FieldMetadata variable_metadata = 1; /* Metadata about the variable to set */
  required bytes variable_value = 2; /* Value to set variable */
}

/*
 * Base message class for a Statement.  A Transaction is composed of
 * one or more Statement messages.  The transaction message represents
 * a single atomic unit of change in the server's state.  Depending on 
 * whether the server/connection is in AUTOCOMMIT mode or not, a 
 * Transaction message may contain one or more than one Statement message.
 */
message Statement
{
  enum Type
  {
    ROLLBACK = 0; /* A ROLLBACK indicator */
    INSERT = 1; /* An INSERT statement */
    DELETE = 2; /* A DELETE statement */
    UPDATE = 3; /* An UPDATE statement */
    TRUNCATE_TABLE = 4; /* A TRUNCATE TABLE statement */
    CREATE_SCHEMA = 5; /* A CREATE SCHEMA statement */
    ALTER_SCHEMA = 6; /* An ALTER SCHEMA statement */
    DROP_SCHEMA = 7; /* A DROP SCHEMA statement */
    CREATE_TABLE = 8; /* A CREATE TABLE statement */
    ALTER_TABLE = 9; /* An ALTER TABLE statement */
    DROP_TABLE = 10; /* A DROP TABLE statement */
    SET_VARIABLE = 98; /* A SET statement */
    RAW_SQL = 99; /* A raw SQL statement */
  }
  required Type type = 1; /* The type of the Statement */
  required uint64 start_timestamp = 2; /* Nanosecond precision timestamp of when the 
                                          Statement was started on the server */
  required uint64 end_timestamp = 3; /* Nanosecond precision timestamp of when the
                                        Statement finished executing on the server */
  optional string sql = 4; /* May contain the original SQL string */
  
  /*
   * Each Statement message may contain one or more of
   * the below sub-messages, depending on the Statement's type.
   */
  optional InsertHeader insert_header = 5;
  optional InsertData insert_data = 6;
  optional UpdateHeader update_header = 7;
  optional UpdateData update_data = 8;
  optional DeleteHeader delete_header = 9;
  optional DeleteData delete_data = 10;
  optional TruncateTableStatement truncate_table_statement = 11;
  optional CreateSchemaStatement create_schema_statement = 12;
  optional DropSchemaStatement drop_schema_statement = 13;
  optional AlterSchemaStatement alter_schema_statement = 14;
  optional CreateTableStatement create_table_statement = 15;
  optional AlterTableStatement alter_table_statement = 16;
  optional DropTableStatement drop_table_statement = 17;  
  optional SetVariableStatement set_variable_statement = 18;  
}

/*
 * Represents a collection of Statement messages that
 * has been executed atomically on a server.
 *
 * @note
 *
 * For bulk operations, the transaction may contain only
 * a data segment, and the atomic guarantee can only be enforced by XA.
 */
message Transaction
{
  required TransactionContext transaction_context = 1;
  repeated Statement statement = 2;
}