Migrating Oracle users to Cloud SQL for MySQL: Terminology and functionality

This document is part of a series that provides key information and guidance related to planning and performing Oracle® 11g/12c database migrations to Cloud SQL for MySQL version 5.7, second-generation instances. The series includes the following parts:

Terminology

This section details the similarities and differences in database terminology between Oracle and Cloud SQL for MySQL. It reviews and compares core aspects of each of the database platforms. The comparison distinguishes between Oracle versions 11g and 12c, due to architectural differences (for example, Oracle 12c introduces the multi-tenant feature). The Cloud SQL for MySQL version referenced here is 5.7.x.

Differences in terminology between Oracle 11g and Cloud SQL for MySQL

Oracle 11g Description Cloud SQL for MySQL Key differences
Instance A single Oracle 11g instance can hold only one database. Instance One MySQL instance can hold multiple databases.
Database A database qualifies as a single instance (the name of the database is identical to the instance name). Database Multiple or single databases serve multiple applications.
Schema Schema and users are identical because both are considered to be the owners of database objects (a user can be created without specifying or being allocated to a schema). Schema A schema is referred to as a database, while database objects are created under a certain schema/database.
User Identical to schema because both are owners of database objects—for example, instance → database → schemas/users → database objects. User A database user with specific permissions to connect or modify database objects on specific schemas/databases—for example, instance → databases/schemas → database objects.
Role Defined set of database permissions that can be chained as a group and can be assigned to database users. MySQL privileges MySQL 5.7 does not support roles management. Permissions can be configured using the GRANT clause for users to have privileges on database objects at different levels (READ/WRITE, etc.).
Admin/SYSTEM users Oracle administrator users with the highest level of access:
SYS
SYSTEM
Super users Once deployed, Cloud SQL for MySQL has the root@'%' user (can connect from any host) and an additional user named mysql.sys, which can connect only from the localhost.
Dictionary/metadata Oracle uses the following metadata tables:
USER_TableName
ALL_TableName
DBA_TableName
Dictionary/metadata MySQL uses several databases/schemas for dictionary/metadata:
MYSQL
INFORMATION_SCHEMA
PERFORMANCE_SCHEMA
SYS
Each of these databases are also system databases and are created with each Cloud SQL for MySQL deployment.
System dynamic views Oracle dynamic views:
V$ViewName
System dynamic views MySQL dynamic views can be found in several of the system databases:
INFORMATION_SCHEMA
PERFORMANCE_SCHEMA
SYS
Tablespace The primary logical storage structures of Oracle databases; each tablespace can hold one or more data files. Tablespace Similar to Oracle, a MySQL tablespace is a logical unit, but represents only a single table, unlike the Oracle tablespace, which can have multiple data files (holds data for multiple tables).

MySQL supports the creation of a new tablespace with an allocated data file, then creating a new table attached to the newly created tablespace. Note that tablespace configuration settings such as sizing and limits are set using database parameters and not during tablespace creation.
Data files The physical elements of an Oracle database that hold the data and are defined under a specific tablespace.

A single data file is defined by the initial size and max size and can hold data for multiple tables.

Oracle data files uses the .dbf suffix (not mandatory).
Data files Cloud SQL for MySQL uses the innodb_file_per_table parameter with the value "ON" (default); this configuration generates a new data file for each table and a dedicated tablespace.

MySQL data files use .ibd (data) and .frm (metadata) files.
System tablespace Contains the data dictionary tables and views objects for the entire Oracle database. System tablespace Same as Oracle, contains the dictionary/metadata tables. Stored in the innodb_system tablespace attached with the ibdata1 data file.
Temporary tablespace Contains schema objects valid for the duration of a session; in addition, it supports running operations that cannot fit in server memory. Temporary tablespace Purpose is identical to Oracle, stored in MySQL innodb_temporary tablespace attached with the ibtmp1 data file.
Undo
tablespace
A special type of system-permanent tablespace used by Oracle to manage rollback operations when running the database in automatic undo management mode (default). Undo tablespace Similar to Oracle, MySQL Undo tablespace contains undo logs for rollback purposes. By default, this option is set to OFF and mentioned as deprecated for future MySQL releases.
ASM Oracle Automatic Storage Management is an integrated, high-performance database file system and disk manager all run automatically by an Oracle database configured with ASM. Not supported MySQL uses the term storage engines to describe different data handling implementations, but does not support Oracle ASM. Cloud SQL for MySQL supports many features that provide storage automation, such as automatic storage increases, performance, and scalability.
Tables/views User-created fundamental database objects. Tables/views Identical to Oracle.
Materialized views Defined with specific SQL statements and can be manually or automatically refreshed based on specific configurations. Not supported by MySQL As a workaround, triggers/views can be used instead of Oracle materialized views.
Sequence Oracle unique value generator. Auto increment MySQL does not support Oracle sequences; use the AUTO_INCREMENT as an alternative solution to automatic sequence generation functionality.
Synonym Oracle database objects that serve as alternative identifiers for other database objects. Not supported MySQL does not support Oracle Synonym; as a workaround, views can be used while setting the appropriate permissions.
Partitioning Oracle provides many partitioning solutions for splitting large tables into smaller managed pieces. Partitioning MySQL has more limited partitioning support to improve performance, while retaining data management and maintenance operations, like Oracle partitions.
Flashback database Oracle proprietary feature that can be used to initialize an Oracle database to a previous defined time, allowing you to query or restore data that was modified or corrupted by mistake. Not supported For an alternative solution, you can use Cloud SQL backups and point-in-time recovery to restore a database to a previous state (for example, restoring before a table drop).
sqlplus Oracle command-line interface that lets you query and manage the database instance. mysql MySQL-equivalent command line-interface for querying and managing. Can be connected from any client with the appropriate permissions to Cloud SQL.
PL/SQL Oracle extended procedural language to ANSI SQL. MySQL MySQL has its own extended procedural language with different syntax and implementation, and does not have additional naming for this extended language.
Package & package body Oracle-specific functionality to group stored procedures and functions under the same logical reference. Not supported MySQL supports stored procedures and functions as single objects with group allocation.
Stored procedures & functions Uses PL/SQL to implement code functionality. Stored procedure & functions The creation of stored procedures and functions is supported by MySQL with its proprietary procedural language implementation.
Trigger Oracle object used to control DML implementation over tables. Trigger Identical to Oracle.
PFILE/SPFILE Oracle instance and database level parameters are kept in a binary file known as the SPFILE (in previous versions, the file was called PFILE), which can be used as a text file for setting parameters manually. Cloud SQL for MySQL database flags You can set or modify Cloud SQL for MySQL parameters through the database flags utility. You cannot change database parameters in Cloud SQL for MySQL by using the MySQL client command-line interface (for example, mysql> SET GLOBAL ...). You can change these parameters only by using the database flags utility.
SGA/PGA/AMM Oracle memory parameters that control memory allocation to the database instance. INNODB_BUFFER_POOL_SIZE MySQL has its own memory parameters. An equivalent parameter could be INNODB_BUFFER_POOL_SIZE. In Cloud SQL for MySQL, this parameter is predefined by the chosen instance type, and the value changes accordingly.
Result Cache Reduces SQL I/O operations by retrieving rows from the buffer cache, which can be managed using database parameters and hints at the session level. Query Cache Has the same fundamental purpose as Oracle Result Cache and can be managed at the database level and at the session level.
Database hints Controlled impact to SQL statements that influence the optimizer's behavior in order to achieve better performance. Oracle has more than 50 different database hints. Database hints MySQL supports a limited set of database hints in comparison to Oracle (optimizer hints and index hints). Note that MySQL uses different database hints, syntax, and naming.
RMAN Oracle Recovery Manager utility. Used to take database backups with extended functionality to support multiple disaster recovery scenarios and more (cloning, etc.). Cloud SQL for MySQL Backup Cloud SQL for MySQL offers two methods for applying full backup: on-demand and automated backups.
Data Pump (EXPDP/IMPDP) Oracle dump generation utility that can be used for many features, such as export/import, database backup (at the schema or object level), schema metadata, generate schema SQL files and more.
mysqldump/mysqlimport
MySQL dump (export) utility that can be connected as a client (remotely) and generate a dump file (SQL). Later, you can compress the dump file and move it to Cloud Storage. The mysqldump utility is for the export step only.
SQL*Loader Tool that provides the ability to upload data from external files such as text files, CSV files, and more.
mysqlimport/
LOAD FILE INFILE
The mysqlimport utility provides the ability to load text or CSV files (Oracle supports additional file formats) into a database table with a corresponding structure.
Data Guard Oracle disaster recovery solution using a standby instance, enabling users to perform `READ` operations from the standby instance. Cloud SQL for MySQL high availability and replication To achieve disaster recovery or high availability, Cloud SQL for MySQL offers the failover replica architecture and for read-only operations (READ/WRITE separation) using the Read Replica.
Active Data Guard/Golden Gate Oracle's main replication solutions, which can serve multiple purposes such as Standby (DR), Read-Only instance, Bi-Directional replication (multi-source), data warehousing, and more. Cloud SQL for MySQL Read Replica Cloud SQL for MySQL Read Replica to implement clustering with READ/WRITE separation. Currently, there is no support for multi-source configuration, such as Golden Gate Bi-Directional replication, or heterogeneous replication.
RAC Oracle Real Application Cluster. Oracle proprietary clustering solution for providing high availability by deploying multiple database instances with a single storage unit. Not supported Multi-source architecture is not yet supported in Google Cloud Cloud SQL. To achieve clustering architecture with READ/WRITE separation and high availability, use Cloud SQL high availability and read replica.
Grid/Cloud Control (OEM) Oracle software for managing and monitoring databases and other related services in a web app format. This tool is useful for real-time database analysis to understand high workloads. Cloud SQL for MySQL Console, Cloud Monitoring Use Cloud SQL for MySQL for monitoring, including detailed time and resources-based graphs. Also use Cloud Monitoring to hold specific MySQL monitoring metrics and logs analysis for advanced monitoring capabilities.
REDO logs Oracle transaction logs that consist of two (or more) pre-allocated defined files that store all data modifications as they occur. The purpose of the redo log is to protect the database in case of an instance failure. REDO logs MySQL also has redo logs files, which are used during crash recovery to correct data written by incomplete transactions' redo logs mechanism.
Archive logs Archive logs provide support for backup and replication operations and more. Oracle writes to archive logs (if enabled) after each redo log switch operation. binlogs MySQL implementation of transaction logs retention. Used mainly for replication purposes (enabled by default with Cloud SQL).
Control file The Oracle control file holds information about the database, such as data files, redo logs names, and locations, the current log sequence number, and information about the instance checkpoint. MySQL MySQL architecture doesn't include a control file similar to Oracle implementation. This is controlled through the MySQL parameters and by using the SHOW MASTER STATUS command in order to see the current binary log position.
SCN Oracle SCN (System Change Number) is the primary method of maintaining data consistency by all Oracle database components in order to satisfy the ACID model of transaction. Log Sequence Number MySQL implementation for database consistency uses the LSN (Log Sequence Number).
AWR Oracle AWR (Automatic Workload Repository) is a verbose report providing detailed information about Oracle database instance performance and is considered a DBA tool for performance diagnostics.
performance_schema
MySQL doesn't have a report equivalent to Oracle AWR, but MySQL gathers performance data collected by performance_schema. An alternative solution would be to use MySQL Workbench performance dashboards.
DBMS_SCHEDULER
Oracle utility used to set and time predefined operations.
EVENT_SCHEDULER
MySQL database internal scheduler functionality. By default, this feature is set to OFF.
Transparent data encryption Encrypts data stored on disks as data-at-rest protection. Cloud SQL Advanced Encryption Standard Cloud SQL for MySQL uses the 256-bit Advanced Encryption Standard (AES-256) for data-at-rest security protection, as well as for in-transit data
Advanced compression To improve the database storage footprint, reduce storage costs, and improve database performance, Oracle provides data (tables/indexes) advanced compression capabilities. InnoDB table compression MySQL offers table compression by creating a table using the ROW_FORMAT parameter set to COMPRESSED. Read more about index compression.
SQL Developer Oracle free SQL GUI for managing and running SQL and PL/SQL statements (can be used with MySQL as well). MySQL Workbench MySQL free SQL GUI for managing and running SQL and MySQL code statements.
Alert Log Oracle main log for general database operations and errors. MySQL Error Log Uses Cloud Logging Logs Viewer to watch MySQL error logs
DUAL table Oracle special table holding mostly for retrieving pseudo column values such as SYSDATE or USER DUAL table MySQL allows DUAL to be specified as a table in SQL statements that do not depend on data from any tables.
External table Oracle allows users to create external tables having the source data on files outside the database. Not supported. No direct equivalent.
Listener Oracle network process tasked with listening for incoming database connections Cloud SQL Authorized networks MySQL accepts connections from remote sources once allowed in the Cloud SQL Authorized Networks configuration page
TNSNAMES Oracle network configuration file that defines database addresses for establishing connections by using connection aliases. Does not exist MySQL accepts external connections using the Cloud SQL Instance connection name or private/public IP address. Cloud SQL Proxy is an additional secure access method to connect to Cloud SQL for MySQL (second-generation instances) without having to allow specific IP addresses or configure SSL.
Instance default port 1521 Instance default port 3306
Database link Oracle schema objects which can be used to interact with local/remote database objects. Not supported For an alternative workaround, use application code to connect and retrieve data from a remote database.

Differences in terminology between Oracle 12c and Cloud SQL for MySQL

Oracle 12c Description Cloud SQL for MySQL Key differences
Instance The multi-tenant ability introduced in Oracle 12c instance that can hold multiple databases as a pluggable database (PDB), as opposed to Oracle 11g, where an Oracle instance can only obtain one database. Instance Cloud SQL for MySQL can hold multiple databases with different naming serving multiple services and applications.
CDB A multi-tenant container database (CDB) can support one or more PDBs, while CDB global objects (affects all PDBs) can be created, such as roles. MySQL Instance The MySQL instance is comparable to the Oracle CDB. Both provide a system layer for the PDBs.
PDB PDBs (pluggable databases) can be used to isolate services and applications from one another and can be used as a portable collection of schemas. MySQL databases/schemas A MySQL database can serve multiple services and applications as well as many database users.
Session sequences Starting with Oracle 12c, sequences can be created at the session level (return unique values only within a session) or at the global level (for example, when using temporary tables). Auto
increment
Sequences are not supported by MySQL, but users can use the AUTO_INCREMENT column property as an alternate solution.
Identity columns The Oracle 12c IDENTITY type generates a sequence and associates it with a table column without the need to manually create a separate sequence object. Auto increment Use the AUTO_INCREMENT column property to simulate the same functionality as Oracle 12c identity column (an alternative solution to automatic sequence generation functionality).
Sharding Oracle sharding is a solution in which one Oracle database is partitioned into multiple smaller databases (shards) to allow scalability, availability, and geo-distribution for OLTP environments. Not supported (as a feature) MySQL does not have an equivalent sharding feature. Sharding can be implemented using MySQL (as the data platform) with a supporting application layer.
In-memory database Oracle provides a suite of features which can improve database performance for OLTP as well for and mixed workloads. Not supported MySQL does not have an equivalent feature. You can use Memorystore as an alternative.
Redaction As part of Oracle's advanced security features, redaction can perform column masking to prevent sensitive data from being displayed by users and applications. Not supported MySQL does not have an equivalent feature.

Functionality

Although Oracle 11g/12c and Cloud SQL for MySQL databases work on different architectures (infrastructure and extended procedural languages), they share the same fundamental aspects of a relational database. They support database objects, multi-user concurrency workloads, and transactions (ACID compatibility). They also manage locking contentions that support multiple isolation levels (based on the business needs), and they serve ongoing application requirements as a relational data store for Online Transactional Processing (OLTP) operations and Online Analytical Processing (OLAP).

The following section provides an overview of some of the main functional differences between Oracle and Cloud SQL for MySQL. In some cases, where needed, the section includes detailed technical comparisons.

Creating and viewing existing databases

Oracle 11g/12c Cloud SQL for MySQL 5.7
You usually create databases, and view existing ones, by using the Oracle Database Creation Assistant (DBCA) utility. Manually created databases or instances require that you specify additional parameters:
SQL> CREATE DATABASE ORADB
     USER SYS IDENTIFIED BY password
     USER SYSTEM IDENTIFIED BY password
     EXTENT MANAGEMENT LOCAL
     DEFAULT TEMPORARY TABLESPACE temp
     UNDO TABLESPACE undotbs1
     DEFAULT TABLESPACE users;
Use a statement of the form CREATE DATABASE Name;, as in this example:
mysql> CREATE DATABASE MYSQLDB;
Oracle 12c Cloud SQL for MySQL 5.7
In Oracle 12c, you can create PDBs from the seed, either from a container database (CDB) template or by cloning a PDB from an existing PDB. You use several parameters:

SQL> CREATE PLUGGABLE DATABASE PDB
     ADMIN USER usr IDENTIFIED BY passwd
     ROLES = (dba)
     DEFAULT TABLESPACE sales
     DATAFILE '/disk1/ora/dbs/db/db.dbf'
     SIZE 250M AUTOEXTEND ON
     FILE_NAME_CONVERT =
     ('/disk1/oracle/dbs/pdbseed/',
      '/disk1/oracle/dbs/salespdb/')
      STORAGE (MAXSIZE 2G)
      PATH_PREFIX =
      '/disk1/oracle/dbs/salespdb/';
Use a statement of the form CREATE DATABASE Name;, as in this example:
mysql> CREATE DATABASE MYSQLDB;
List all PDBs:
SQL> SHOW is PDBS;
List all existing databases:
mysql> SHOW DATABASES;
Connect to a different PDB:
SQL> ALTER SESSION SET CONTAINER=pdb;
Connect to a different database:
mysql> use databaseName;
Or:
mysql> \u databaseName;
Open or close a specific PDB (open/read-only):
SQL> ALTER PLUGGABLE DATABASE pdb CLOSE;
Not supported for a single database.

All databases are under the same Cloud SQL for MySQL instance; thus, all databases are all up or all down.

Managing a database through the Cloud SQL console

  • In the Cloud Console, go to Storage > SQL > Instance > Databases > View/Create.

    Console page for creating/viewing a MySQL database.

System databases and schemas

Oracle database instances obtain certain system schemas—for example, SYS/SYSTEM—with the owners role of database metadata objects.

In contrast, MySQL holds several system databases (as opposed to Oracle schemas), which serve the metadata layer (note that the database names are case sensitive):

  • Mysql

    The mysql system database holds tables that store information required by the MySQL server as it runs, such as the following:

    • System privileges tables
    • Objects information tables
    • Log system tables
    • Replication system tables
    • Optimizer system tables
    • Time zone system tables
  • INFORMATION_SCHEMA

    INFORMATION_SCHEMA serves as the main database data dictionary and system catalog. It provides access to database metadata, which is internal database information about the MySQL server, such as the name of a database or table, the column data type, and the access privileges.

  • performance_schema

    A system database that collects statistical information about the MySQL instance. The performance_schema system database holds metrics for server execution monitoring at a very granular level. The schema provides server internal execution inspection at run time, and it can serve as the main source for analyzing database performance issues.

    The performance_schema is not enabled by default using Cloud SQL for MySQL. To enable the schema, use the gcloud command-line tool:

    gcloud sql instances patch INSTANCE_NAME --database-flags performance_schema=on
    

    To complete this configuration, you must reboot the instance. You cannot modify the --database-flags parameter by using the Cloud SQL for MySQL database flags page in the Cloud Console.

  • sys

    The sys schema exists from MySQL version 5.5.7 and holds mainly views on the performance_schema system tables. This schema provides a more readable set of views that summarize performance_schema data into a more easily understandable form. The sys schema also holds several stored procedures and functions to perform operations such as configuring performance_schema and generating diagnostic reports.

    The sys schema displays information only when the performance_schema is enabled.

Viewing metadata and system dynamic views

This section provides an overview of some of the most common metadata tables and system dynamic views used in Oracle and their corresponding database objects in Cloud SQL for MySQL version 5.7.

Oracle provides hundreds of system metadata tables and views, while MySQL only holds several dozen. For each case, there can be more than one database object, serving a specific purpose.

Oracle provides several levels of metadata objects, each requiring different privileges:

  • USER_TableName: Can be viewed by the user.
  • ALL_TableName: Can be viewed by all users.
  • DBA_TableName: Can be viewed only by users with the DBA privilege, such as SYS and SYSTEM.

For dynamic performance views, Oracle uses the V$ and GV$ prefixes. For a MySQL user to be able to view system metadata tables or views, they must have specific permissions on system objects. For more information about security, see the Security section.

Metadata type Oracle table/view MySQL table/view/show (MySQL CMD)
Open sessions
V$SESSION
SHOW PROCESSLIST
INFORMATION_SCHEMA.PROCESSLIST
performance_schema.threads
Running transactions
V$TRANSACTION
INFORMATION_SCHEMA.INNODB_TRX
Database objects
DBA_OBJECTS
Not supported. Query each object by its type.
Tables
DBA_TABLES
INFORMATION_SCHEMA.TABLES
INFORMATION_SCHEMA.INNODB_SYS_TABLES
Table columns
DBA_TAB_COLUMNS
INFORMATION_SCHEMA.COLUMNS
INFORMATION_SCHEMA.INNODB_SYS_COLUMNS
Table and column privileges
TABLE_PRIVILEGES
DBA_COL_PRIVS
ROLE_TAB_PRIVS
INFORMATION_SCHEMA.COLUMN_PRIVILEGES
Partitions
DBA_TAB_PARTITIONS
DBA_TAB_SUBPARTITIONS
INFORMATION_SCHEMA.PARTITIONS
SHOW CREATE TABLE TableName
SHOW TABLE STATUS LIKE 'TableName'
Views
DBA_VIEWS
INFORMATION_SCHEMA.VIEWS
Constraints
DBA_CONSTRAINTS
INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS
SHOW CREATE TABLE TableName
Indexes
DBA_INDEXES
DBA_PART_INDEXES
INFORMATION_SCHEMA.STATISTICS
INFORMATION_SCHEMA.INNODB_SYS_INDEXES
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
Materialized views
DBA_MVIEWS
Not supported
Stored procedures
DBA_PROCEDURES
INFORMATION_SCHEMA.ROUTINES
Stored functions
DBA_PROCEDURES
INFORMATION_SCHEMA.ROUTINES
Triggers
DBA_TRIGGERS
INFORMATION_SCHEMA.TRIGGERS
Users
DBA_USERS
mysql.user
User privileges
DBA_SYS_PRIVS
DBA_ROLE_PRIVS
SESSION_PRIVS
INFORMATION_SCHEMA.USER_PRIVILEGES
Jobs/
Scheduler
DBA_JOBS
DBA_JOBS_RUNNING
DBA_SCHEDULER_JOBS
DBA_SCHEDULER_JOB_LOG
INFORMATION_SCHEMA.EVENTS
Tablespaces
DBA_TABLESPACES
INFORMATION_SCHEMA.INNODB_SYS_TABLESPACES
Data files
DBA_DATA_FILES
INFORMATION_SCHEMA.FILES
INFORMATION_SCHEMA.INNODB_SYS_DATAFILES
Synonyms
DBA_SYNONYMS
Not supported
Sequences
DBA_SEQUENCES
Not supported
Database links
DBA_DB_LINKS
Not supported
Statistics
DBA_TAB_STATISTICS
DBA_TAB_COL_STATISTICS
DBA_SQLTUNE_STATISTICS
DBA_CPU_USAGE_STATISTICS
INFORMATION_SCHEMA.STATISTICS
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
SHOW INDEXES FROM TableName
Locks
DBA_LOCK
DBA_DDL_LOCKS
DBA_DML_LOCKS
V$SESSION_BLOCKERS
V$LOCKED_OBJECT
INFORMATION_SCHEMA.INNODB_LOCKS
INFORMATION_SCHEMA.INNODB_LOCK_WAITS
INFORMATION_SCHEMA.INNODB_TRX
performance_schema.metadata_locks
performance_schema.rwlock_instances
SHOW PROCESSLIST
Database parameters
V$PARAMETER
V$NLS_PARAMETERS
SHOW PARAMETER Param
performance_schema.global_variables
performance_schema.session_variables
INFORMATION_SCHEMA.CHARACTER_SETS
SHOW VARIABLES LIKE '%variable%';
Segments
DBA_SEGMENTS
Segments table is not supported. Query each object by its type.
Roles
DBA_ROLES
DBA_ROLE_PRIVS
USER_ROLE_PRIVS
Roles not supported use instead:
information_schema.COLUMN_PRIVILEGES
information_schema.SCHEMA_PRIVILEGES
information_schema.TABLE_PRIVILEGES
information_schema.USER_PRIVILEGES
mysql.columns_priv
mysql.procs_priv
mysql.proxies_priv
mysql.tables_priv
Session history
V$ACTIVE_SESSION_HISTORY
DBA_HIST_*
sys.statement_analysis
performance_schema.events_stages_history
performance_schema.events_stages_history_long
performance_schema.events_statements_history
performance_schema.events_statements_history_long
performance_schema.events_transactions_history
performance_schema.events_transactions_history_long
performance_schema.events_waits_history
performance_schema.events_waits_history_long
Version
V$VERSION
sys.version
SHOW VARIABLES LIKE '%version%';
Wait events
V$WAITCLASSMETRIC
V$WAITCLASSMETRIC_HISTORY
V$WAITSTAT
V$WAIT_CHAINS
performance_schema.events_waits_current
performance_schema.events_waits_history
performance_schema.events_waits_history_long
sys.innodb_lock_waits
sys.io_global_by_wait_by_bytes
sys.io_global_by_wait_by_latency
sys.schema_table_lock_waits
sys.wait_classes_global_by_avg_latency
sys.wait_classes_global_by_latency
sys.waits_by_host_by_latency
sys.waits_by_user_by_latency
sys.waits_global_by_latency
SQL tuning and
analyzing
V$SQL
V$SQLAREA
V$SESS_IO
V$SYSSTAT
V$STATNAME
V$OSSTAT
V$ACTIVE_SESSION_HISTORY
V$SESSION_WAIT
V$SESSION_WAIT_CLASS
V$SYSTEM_WAIT_CLASS
V$LATCH
V$SYS_OPTIMIZER_ENV
V$SQL_PLAN
V$SQL_PLAN_STATISTICS
performance_schema.events_statements_current
performance_schema.events_statements_history
performance_schema.events_statements_history_long
sys.statement_analysis
sys.host_summary_by_statement_latency
sys.host_summary_by_statement_type
sys.statements_with_errors_or_warnings
sys.statements_with_full_table_scans
sys.statements_with_runtimes_in_95th_percentile
sys.statements_with_sorting
sys.statements_with_temp_tables
sys.user_summary_by_statement_latency
sys.user_summary_by_statement_type
slow-query-log
general-log
SHOW STATUS LIKE '%StatusName%';
Instance
memory tuning
V$SGA
V$SGASTAT
V$SGAINFO
V$SGA_CURRENT_RESIZE_OPS
V$SGA_RESIZE_OPS
V$SGA_DYNAMIC_COMPONENTS
V$SGA_DYNAMIC_FREE_MEMORY
V$PGASTAT
information_schema.INNODB_CMPMEM_RESET
information_schema.INNODB_CMPMEM
performance_schema.memory_summary_by_account_by_event_name
performance_schema.memory_summary_by_host_by_event_name
performance_schema.memory_summary_by_thread_by_event_name
performance_schema.memory_summary_by_user_by_event_name
performance_schema.memory_summary_global_by_event_name
performance_schema.replication_group_member_stats
performance_schema.replication_group_members
sys.memory_by_host_by_current_bytes
sys.memory_by_thread_by_current_bytes
sys.memory_by_user_by_current_bytes
sys.memory_global_by_current_bytes
sys.memory_global_total

MySQL storage engines

Unlike many other RDBMS (including Oracle's), MySQL can work polymorphically due to its pluggable storage system. The MySQL pluggable storage engine architecture enables a database administrator to select a specialized storage engine for a particular application need.

The MySQL pluggable storage engine component in the MySQL database server is responsible for performing the data I/O operations, including storing the data into the disks or memory buffers. The pluggable storage engine architecture provides a standard set of management and support services that are common among all underlying storage engines.

From MySQL version 5.5 and higher, the default storage engine is the InnoDB storage engine, while InnoDB is also handling the temporary tables. You can configure storage engines during table CREATE or ALTER, as in the following example:

mysql> SHOW CREATE TABLE JOBS \G;

The output is the following:

*************************** 1. row ***************************
       Table: JOBS
Create Table: CREATE TABLE `JOBS` (
  `JOB_ID` varchar(10) NOT NULL,
  `JOB_TITLE` varchar(35) NOT NULL,
  `MIN_SALARY` decimal(6,0) DEFAULT NULL,
  `MAX_SALARY` decimal(6,0) DEFAULT NULL,
  PRIMARY KEY (`JOB_ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

For more information, see MySQL different storage engines.
You can view the storage engine configuration by using the following query:

mysql> SHOW VARIABLES LIKE '%storage%';

The output is similar to the following:

+----------------------------------+--------+
| Variable_name                    | Value  |
+----------------------------------+--------+
| default_storage_engine           | InnoDB |
| default_tmp_storage_engine       | InnoDB |
| disabled_storage_engines         |        |
| enforce_storage_engine           | Innodb |
| internal_tmp_disk_storage_engine | InnoDB |
+----------------------------------+--------+

You can view all built-in storage engines:

mysql> SHOW STORAGE ENGINES;

The output is similar to the following:

+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

Note that InnoDB is the default storage engine, and is the only storage engine to support transactions (ACID compliant). Because InnoDB is the only storage engine that approximates Oracle functionality, we recommend that you use InnoDB at all times. Cloud SQL for MySQL Second Generation supports only the InnoDB storage engine.

System parameters

Both Oracle and Cloud SQL for MySQL databases can be specifically configured to achieve certain functionality beyond the default configuration. To alter configuration parameters in Oracle, certain administration permissions are required (primarily the SYS/SYSTEM user permissions).

Following is an example of altering the Oracle configuration by using the ALTER SYSTEM statement. In this example, the user changes the "maximum attempts for failed logins" parameter at the spfile configuration level only (with the modification valid only after after a reboot):

SQL> ALTER SYSTEM SET SEC_MAX_FAILED_LOGIN_ATTEMPTS=2 SCOPE=spfile;

In the next example, the user is requesting to simply view the Oracle parameter value:

SQL> SHOW PARAMETER SEC_MAX_FAILED_LOGIN_ATTEMPTS;

The output is similar to the following:

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
sec_max_failed_login_attempts        integer     2

The Oracle parameter modification works in three scopes:

  • SPFILE: Parameter modifications are written to the Oracle spfile, with an instance reboot required for the parameter to take effect.
  • MEMORY: Parameter modifications are applied in the memory layer only while no static parameter change is allowed.
  • BOTH: Parameter modifications are applied in both the server parameter file and in the instance memory, where no static parameter change is allowed.

Cloud SQL for MySQL configuration flags

You can modify the Cloud SQL for MySQL system parameters by using the configuration flags in the Cloud Console, the gcloud tool, or CURL. See the complete list of all parameters supported by Cloud SQL for MySQL that you can alter.

MySQL parameters can be divided into several scopes:

  • Dynamic parameters: Can be altered at run time.
  • Static parameters: Require an instance reboot to take effect.
  • Global parameters: Will have a global effect on all current and future sessions.
  • Session parameters: Can be altered at the session level for the current session lifetime only, isolated from other sessions.

The Cloud SQL for MySQL memory parameter innodb_buffer_pool_size (one of the crucial parameters to consider when planning and sizing a MySQL environment) is determined by the instance type and cannot be altered by using the configuration flags or by any other method—for example:

  • Instance type db-n1-standard-1 has 1.4 GB of memory allocation.
  • Instance type db-n1-highmem-8 has 38 GB of memory allocation.

Examples of altering Cloud SQL for MySQL parameters

Console

Use the Cloud Console to enable the event_scheduler parameter.

  1. Go to the Edit instance page of Cloud Storage.

    Go to Edit instance

  2. Under Flags, click Add item and search for event_scheduler as in the following screenshot.

    Edit the event scheduler instance in the console.

gcloud

  • Use the gcloud tool to enable the event_scheduler parameter.:

    gcloud sql instances patch INSTANCE_NAME \
        --database-flags event_scheduler=on
    

    The output is the following:

    WARNING: This patch modifies database flag values, which may require
    your instance to be restarted. Check the list of supported flags -
    /sql/docs/mysql/flags - to see if your
    instance will be restarted when this patch is submitted.
    
    Do you want to continue (Y/n)?
    

MySQL session

Disable AUTOCOMMIT mode at the session level. This alteration stays in effect for the current session and holds for the session lifetime only.

  1. Show variables like autocommit:

    mysql> SHOW VARIABLES LIKE '%autoc%';
    

    You see the following output, where autocommit is ON:

    +---------------+-------+
    | Variable_name | Value |
    +---------------+-------+
    | autocommit    | ON    |
    +---------------+-------+
    
  2. Disable autocommit:

    mysql> SET autocommit=off;
    
  3. Show variables like autocommit:

    mysql> SHOW VARIABLES LIKE '%autoc%';
    

    You see the following output, where autocommit is OFF:

    +---------------+-------+
    | Variable_name | Value |
    +---------------+-------+
    | autocommit    | OFF   |
    +---------------+-------+
    

Transactions and isolation levels

This section describes the main differences between Oracle and Cloud SQL for MySQL relevant to transaction and isolation level migrations.

Commit mode

Oracle works by default in non-autocommit mode, where each DML transaction must be determined with COMMIT/ROLLBACK statements. One of the fundamental differences between Oracle and MySQL is that MySQL works by default in autocommit mode, and each DML transaction is autocommitted with explicitly specifying the COMMIT/ROLLBACK statements.

To force MySQL to work in a non-autocommit mode, there are several options:

  • When managing transactions within the scope of stored procedures, use the START TRANSACTION clause to enter the same transactional mode same as Oracle.
  • Use the following statement to set the autocommit system parameter to OFF at the session level and explicitly use COMMIT/ROLLBACK statements in DML transactions:

    mysql> SET autocommit=off;
    

Isolation levels

The ANSI/ISO SQL standard (SQL92) defines four levels of isolation. Each level provides a different approach for handling concurrent execution of database transactions:

  • Read Uncommitted: A currently processed transaction can see uncommitted data made by the other transaction. If a rollback is performed, all data is restored to its previous state.
  • Read Committed: A transaction only sees data changes that were committed; uncommitted changes("dirty reads") are not possible.
  • Repeatable Read: A transaction can view changes made by the other transaction only after both transactions issued a COMMIT or both are rolled back.
  • Serializable: The strictest/strongest isolation level. This level locks all records that are accessed, and locks the resource so that records cannot be appended to the table.

Transaction isolation levels manage the visibility of changed data as seen by other running transactions. Also, when the same data is accessed by several concurrent transactions, the selected level of transaction isolation affects the way different transactions interact.

Oracle supports the following isolation levels:

  • Read Committed (default)
  • Serializable
  • Read-Only (not a part of the ANSI/ISO SQL standard (SQL92)

Oracle MVCC (Multiversion Concurrency Control):

  • Oracle uses the MVCC mechanism to provide automatic read consistency across the entire database and all sessions.
  • Oracle relies on the System Change Number (SCN) of the current transaction to obtain a consistent view of the database; therefore, all database queries only return data committed with respect to the SCN at the time of query execution.
  • Isolation levels can be changed at the transaction and session levels.

Here's an example of setting isolation levels:

-- Transaction Level
SQL> SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
SQL> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
SQL> SET TRANSACTION READ ONLY;

-- Session Level
SQL> ALTER SESSION SET ISOLATION_LEVEL = SERIALIZABLE;
SQL> ALTER SESSION SET ISOLATION_LEVEL = READ COMMITTED;

Cloud SQL for MySQL, like Oracle, supports the following four transaction isolation levels specified in the ANSI SQL:92 standard:

  • READ UNCOMMITTED
  • READ COMMITTED
  • REPEATABLE READ (default)
  • SERIALIZABLE

The Cloud SQL for MySQL default isolation level is REPEATABLE READ. Any new data will be available for both only after both transactions issue a COMMIT command. These isolation levels can be altered at SESSION level and at GLOBAL level (global level modification is currently in beta stage using configuration flags).

To verify current isolation levels both at SESSION and GLOBAL levels, use the following statement:

mysql> SELECT @@GLOBAL.tx_isolation, @@tx_isolation;

The output is the following:

+-----------------------+-----------------+
| @@GLOBAL.tx_isolation | @@tx_isolation  |
+-----------------------+-----------------+
| REPEATABLE-READ       | REPEATABLE-READ |
+-----------------------+-----------------+

You can modify the isolation level syntax as follows:

SET [SESSION] TRANSACTION ISOLATION LEVEL [READ WRITE | READ ONLY]
| REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED | SERIALIZABLE]

And you can modify the isolation level at SESSION level:

mysql> SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

       -- Verify

mysql> SELECT @@GLOBAL.tx_isolation, @@tx_isolation;

The output is the following:

+-----------------------+------------------+
| @@GLOBAL.tx_isolation | @@tx_isolation   |
+-----------------------+------------------+
| REPEATABLE-READ       | READ-UNCOMMITTED |
+-----------------------+------------------+

Cloud SQL for MySQL transactions structure

Transactions syntax:

START TRANSACTION
    [transaction_characteristic [, transaction_characteristic] ...]

transaction_characteristic: { WITH CONSISTENT SNAPSHOT | READ WRITE | READ ONLY }
BEGIN [WORK] COMMIT [WORK] [AND [NO] CHAIN] [[NO] RELEASE] ROLLBACK [WORK] [AND [NO] CHAIN] [[NO] RELEASE] SET autocommit = {0 | 1}

Transactions can be implemented with START TRANSACTION or BEGIN.

The WITH CONSISTENT SNAPSHOT option starts a consistent READ transaction, which is effectively the same as issuing a START TRANSACTION, followed by a SELECT from any table. The WITH CONSISTENT SNAPSHOT clause that starts a consistent READ (a READ operation that uses snapshot information to present query results based on a point in time) does not change the transaction isolation level and is supported only by the REPEATABLE READ isolation level.

A consistent READ uses snapshot information to make query results available based on a point-in-time, regardless of modifications performed by concurrent transactions. If queried data has been changed by another transaction, the original data is reconstructed using the undo log. This will assist avoiding locking issues that may reduce concurrency.

With REPEATABLE READ isolation level, the snapshot is based on the time the first READ operation is performed. With the READ COMMITTED isolation level, the snapshot is reset to the time of each consistent READ operation.

Here's an example of transaction and isolation level setting:

mysql> SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
mysql> START TRANSACTION;
mysql> INSERT INTO tbl1 VALUES (1, 'A');
mysql> UPDATE tbl2 SET col1 = 'Done' WHERE KeyColumn = 1;
mysql> COMMIT;