Find open / long-running transactions

Oracle

SELECT s.sid, s.serial#, s.username,
       t.start_time, t.used_ublk AS undo_blocks
FROM v$transaction t
JOIN v$session s ON t.ses_addr = s.saddr
ORDER BY t.start_time;

A high used_ublk means a large transaction is consuming a lot of undo; it may be waiting for a commit/rollback.

PostgreSQL

SELECT pid, usename, state,
       now() - xact_start AS xact_age, query
FROM pg_stat_activity
WHERE xact_start IS NOT NULL
ORDER BY xact_start;

Long transactions in the 'idle in transaction' state block VACUUM and tuple cleanup; monitor them.

MySQL

SELECT trx_id, trx_state, trx_started,
       TIMESTAMPDIFF(SECOND, trx_started, NOW()) AS age_sec,
       trx_mysql_thread_id
FROM information_schema.innodb_trx
ORDER BY trx_started;

Use trx_mysql_thread_id to correlate with PROCESSLIST and KILL it if necessary.

SQL Server

DBCC OPENTRAN;
-- Detailed:
SELECT st.session_id, dt.database_transaction_begin_time
FROM sys.dm_tran_database_transactions dt
JOIN sys.dm_tran_session_transactions st ON st.transaction_id = dt.transaction_id
WHERE dt.database_id = DB_ID()
ORDER BY dt.database_transaction_begin_time;

Long open transactions prevent log truncation and bloat the log file.

MongoDB

db.adminCommand({
  currentOp: 1,
  "transaction": { $exists: true }
})

Long multi-document transactions are aborted automatically after transactionLifetimeLimitSeconds (default 60 s).

Redis

# Not applicable: MULTI/EXEC transactions are short and atomic; they do not stay open.

Redis transactions hold no locks; for long-running single commands, check SLOWLOG.