Performance Schema Summary Tables These are similar to the  COUNT_STAR  and  xxx _TIMER_WAIT  columns, but summarize read-write transactions only. The transaction access mode specifies whether transactions operate in read/write or read-only mode. These are similar to the  COUNT_STAR  and  xxx _TIMER_WAIT  columns, but summarize read-only transactions only. The transaction access mode specifies whether transactions operate in read/write or read-only mode. The transaction summary tables have these indexes: • COUNT_READ_ONLY ,  SUM_TIMER_READ_ONLY ,  MIN_TIMER_READ_ONLY ,  AVG_TIMER_READ_ONLY , MAX_TIMER_READ_ONLY • events_transactions_summary_by_account_by_event_name : •Primary key on ( USER ,  HOST ,  EVENT_NAME ) • events_transactions_summary_by_host_by_event_name : •Primary key on ( HOST ,  EVENT_NAME ) • events_transactions_summary_by_thread_by_event_name : •Primary key on ( THREAD_ID ,  EVENT_NAME ) • events_transactions_summary_by_user_by_event_name : •Primary key on ( USER ,  EVENT_NAME ) • events_transactions_summary_global_by_event_name : •Primary key on ( EVENT_NAME ) •For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows. •For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows. TRUNCATE TABLE  is permitted for transaction summary tables. It has these effects: In addition, each transaction summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_transactions_summary_global_by_event_name . For details, see Section 27.12.8, “Performance Schema Connection Tables” . Transaction event collection occurs without regard to isolation level, access mode, or autocommit mode. Transaction event collection occurs for all non-aborted transactions initiated by the server, including empty transactions. Read-write transactions are generally more resource intensive than read-only transactions, therefore transaction summary tables include separate aggregate columns for read-write and read-only transactions. Resource requirements may also vary with transaction isolation level. However, presuming that only one isolation level would be used per server, aggregation by isolation level is not provided. Transaction Aggregation Rules 5062