Important Tables

performance schema

Table	Description
data_locks	This table contains details of table and records locks at the InnoDB level. It shows all locks currently held or are pending.
data_lock_waits	Like the data_locks table, it shows locks related to InnoDB, but only those waiting to be granted with information on which threads is blocking the request.
metadata_locks	This table contains information about user-level locks, metadata locks, and similar. To record information, the wait/lock/metadata/sql/mdl Performance Schema instrument must be enabled (it is enabled by default in MySQL 8). The OBJECT_TYPE column shows which kind of lock is held, and the LOCK_TYPE column shows the access level.
table_handles	This table holds information about which table locks are currently in effect. The wait/lock/table/sql/handler Performance Schema instrument must be enabled for data to be recorded (this is the default). This table is less frequently used than the other tables.

sys schema

Table	Description
innodb_lock_waits	This view shows ongoing InnoDB row lock waits. It uses the data_locks and data_lock_waits tables.
schema_table_lock_waits	This view shows ongoing metadata and user lock waits. It uses the metadata_locks table.

information schema

Table	Description
INNODB_TRX	This Information Schema view includes details for InnoDB transactions and is the best resource for studying ongoing InnoDB transactions.

Per Usage

TRANSACTION INFORMATION

The transaction tables can be used to find information about individual transactions or aggregated data.

Table	Description
events_transactions_current	Transactions that are ongoing as well as the latest transaction for threads that are still connected but that have not yet started a new transaction.
events_transactions_history	The last ten transactions (can be changed with the performance_schema_events_transactions_history_size) for each existing thread.
events_transactions_history_long	The last 10000 transactions (the performance_schema_events_transactions_history_long_size option) for the instance. It also includes transactions for disconnected threads. The consumer for this table is disabled by default.
INNODB_TRX	This Information Schema view includes details for InnoDB transactions and is the best resource for studying ongoing InnoDB transactions.

There are five transaction summary tables grouping the data globally or by account, host, thread, or user.

Table	Description
events_transactions_summary_global_by_event_name	All transactions aggregated. There is only a single row in this table.
events_transactions_summary_by_account_by_event_name	The transactions grouped by username and hostname.
events_transactions_summary_by_host_by_event_name	The transactions grouped by hostname of the account.
events_transactions_summary_by_thread_by_event_name	The transactions grouped by thread. Only currently existing threads are included.
events_transactions_summary_by_user_by_event_name	The events grouped by the username part of the account.

STATEMENT INFORMATION

The statement tables follow the same pattern as the transaction tables with three tables with information about individual events and several summary tables with aggregate data.
Additionally, there is the threads table .

Table	Description
events_statements_current	The statements currently executing or for idle connections the latest executed query. When executing stored programs, there may be more than one row per connection.
events_statements_history	The last statements for each connection. The number of statements per connection is capped at performance_schema_events_statements_history_size (defaults to 10). The statements for a connection are removed when the connection is closed.
events_statements_history_long	The latest queries for the instance irrespective of which connection executed it. This table also includes statements from connections that have been closed. The consumer for this table is disabled by default. The number of rows is capped at performance_schema_events_statements_history_long_size (defaults to 10000).
threads	Information about all current threads in the instance, both background and foreground threads. You can use this table instead of the SHOW PROCESSLIST command. In addition to the process list information, there are columns showing whether the thread is instrumented, the operating system thread id, and more.

The statement summary tables group the data by the statement digest, event name, user, etc.

Table	Description
events_statements_summary_by_digest	The statement statistics grouped by the default schema and digest.
events_statements_summary_by_account_by_event_name	The statement statistics grouped by the account and event name. The event name shows what kind of statement is executed, for example, statement/sql/select for a SELECT statement executed directly (not executed through a stored program).
events_statements_summary_by_host_by_event_name	The statement statistics grouped by the hostname of the account and the event name.
events_statements_summary_by_program	The statement statistics grouped by the stored program (event, function, procedure, table, or trigger) that executed the statement. This is useful to find the stored programs that perform the most work.
events_statements_summary_by_thread_by_event_name	The statement statistics grouped by thread and event name. Only threads currently connected are included.
events_statements_summary_by_user_by_event_name	The statement statistics grouped by the username of the account and the event name.
events_statements_summary_global_by_event_name	The statement statistics grouped by the event name.
events_statements_histogram_by_digest	Histogram statistics grouped by the default schema and digest.
events_statements_histogram_global	Histogram statistics where all queries are aggregated in one histogram.
prepared_statements_instances	Statistics for prepared statements with one row per prepared statement (the same statement prepared by two threads count as two unique prepared statements).

Of these tables, the events_statements_summary_by_digest is the most used.
One important thing to note is that queries executed as prepared statements are not included in the statement tables, and instead the prepared_statements_instances table must be used to get information about them.
The sys schema includes a view that serves as an advanced process list as well as views returning statements filtered by criteria such as whether they perform full tables scans, performs sorting, etc.

Table	Description
session	This view returns an advanced process list based on the threads and events_statements_current tables with some additional information from other Performance Schema tables. The view includes the current statement for active connections and the last executed statement for idle connections. The rows are returned in descending order according to the process list time and the duration of the previous statement. The session view is particularly useful to understand what is happening right now.
statement_analysis	This view is a formatted version of the events_statements_summary_by_digest table ordered by the total latency in descending order.
statements_with_errors_or_warnings	This view returns the statements that cause errors or warnings. The rows are ordered in descending order by the number of errors and then number of warnings.
statements_with_full_table_scans	This view returns the statements that include a full table scan. The rows are first ordered by the percentage of times no index is used and then by the total latency, both in descending order.
statements_with_runtimes_in_95th_percentile	This view returns the statements that are in the 95th percentile of all queries in the events_statements_summary_by_digest table. The rows are ordered by the average latency in descending order.
statements_with_sorting	This view returns the statements that sort the rows in its result. The rows are ordered by the total latency in descending order.
statements_with_temp_tables	This view returns the statements that use internal temporary tables. The rows are ordered in descending order by the number of internal temporary tables on disk and internal temporary tables in memory.

METADATA INFORMATION

In metadata_locks table, the most commonly encountered object types are GLOBAL and TABLE.

Object Type	Description
ACL_CACHE	For the access control list (ACL) cache.
BACKUP_LOCK	For the backup lock.
CHECK_CONSTRAINT	For the names of CHECK constraints.
COLUMN_STATISTICS	For histograms and other column statistics.
COMMIT	For blocking commits. It is related to the global read lock.
EVENT	For stored events.
FOREIGN_KEY	For the foreign key names.
FUNCTION	For stored functions.
GLOBAL	For the global read lock (triggered by FLUSH TABLES WITH READ LOCK).
LOCKING_SERVICE	For locks acquired using the locking service interface.
PROCEDURE	For stored procedures.
RESOURCE_GROUPS	For the resource groups.
SCHEMA	For schema/databases. These are similar to the metadata locks for tables except they are for a schema.
SRID	For the spatial reference systems (SRIDs).
TABLE	For tables and views. This includes what is called metadata locks in this book.
TABLESPACE	For tablespaces.
TRIGGER	For triggers (on tables).
USER_LEVEL_LOCK	For user-level locks.

Also, METADATA LOCK TYPES are:

Lock Type	Description
INTENTION_EXCLUSIVE	An intention exclusive lock that can later be upgraded to an exclusive lock. This is also used when accessing the dictionary cache.
SHARED	For shared access to only the metadata of the object. For example, used with stored procedures and when preparing prepared statements.
SHARED_HIGH_PRIO	A high-priority shared lock which is used when only accessing the metadata, for example, when populating the Information Schema view with metadata for the tables.
SHARED_READ	A shared lock for cases where it is intended to read the data of the object.
SHARED_WRITE	A shared lock on the metadata for cases where the intention is to modify the data of the object.
SHARED_WRITE_LOW_PRIO	The same as SHARED_WRITE but for statements that use the LOW_PRIORITY clause. This is not supported by InnoDB.
SHARED_UPGRADABLE	A shared lock that allows concurrent read/write of the table data. It can later be upgraded to lock types preventing data changes. It is used by the first phase of ALTER TABLE statements.
SHARED_READ_ONLY	This lock type is used with LOCK TABLES … READ to take a shared lock while preventing modification of the table’s metadata and data.
SHARED_NO_WRITE	Another upgradable shared lock which blocks writes to the data. It is also used with the first phase of ALTER TABLE statements.
SHARED_NO_READ_WRITE	An upgradable lock holding a shared lock on the metadata but prevents both reads and writes of the table data. This is used by LOCK TABLES ... WRITE.
EXCLUSIVE	No other access to neither the metadata nor table data is allowed. This is used with CREATE TABLE, DROP TABLE, and RENAME TABLE statements as well as some phases of other DDL statements.