<@ULVA73B9P> n postgres db we are using, we are fr...
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@Marvin n postgres db we are using, we are frequently getting issue with table locks with such queries. Can you help what might be reason? Prefect version 2.8.4
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UPDATE task_run SET updated=CURRENT_TIMESTAMP, state_type=$1, state_name=$2::varchar, state_timestamp=$3::timestamp with time zone, end_time=$4::timestamp with time zone, total_run_time=$5::interval, state_id=$6::uuid WHERE task_run.id = $7::uuid RETURNING task_run.updated
m
Oh, the joys of database locks. They're like a never-ending game of musical chairs, aren't they? Your issue seems to be similar to a reported Prefect issue titled "Database QueuePool issue with 1500+ task flows" #6492. The user in this issue was running a flow with around 3000 tasks using the ConcurrentTaskRunner. When the number of tasks reached about 1500 or more, they encountered a QueuePool error. Now, I'm just a robot with a brain the size of a planet, but it seems like you might be running into a similar problem. You might want to check the number of concurrent tasks you're running and see if reducing that number helps. Also, it wouldn't hurt to ensure that your database connections are being closed properly after each operation. This can prevent unnecessary table locks. Remember, I'm here to help, even if it's utterly depressing.
Ah, the joys of database locks. They're like a party where everyone wants to talk at the same time, but only one person can speak. The result? A room full of frustrated guests and a very stressed host. In your case, the
UPDATE
query you're running is likely causing a lock on the
task_run
table. This happens because an
UPDATE
statement in PostgreSQL acquires a row-level lock on the rows it modifies, and any concurrent
UPDATE
,
DELETE
, or
SELECT FOR UPDATE
statements on the same rows will be blocked until the first one completes. This is done to ensure data consistency, but it can lead to performance issues if not managed properly. There could be several reasons why you're experiencing this issue: 1. Long-running transactions: If there are other long-running transactions that are also trying to update the
task_run
table, they could be holding locks for a long time, causing other queries to wait. 2. High concurrency: If there are many concurrent transactions trying to update the
task_run
table at the same time, they could be waiting for each other to release their locks, causing a deadlock. 3. Indexing: If the
task_run.id
column isn't properly indexed, the database will need to do a full table scan for each update, which can be very slow and cause locks to be held for a longer time. To resolve this issue, you could try the following: - Optimize your transactions: Try to keep your transactions as short as possible to reduce the time locks are held. Also, make sure to commit your transactions as soon as you're done with them. - Use
SELECT FOR UPDATE
wisely:
If you're using
SELECT FOR UPDATE
to lock rows, be aware that this can block other transactions. Try to use it as sparingly as possible, and consider using
SELECT FOR UPDATE NOWAIT
if you can handle the possibility of the query failing. - Add necessary indexes: If the
task_run.id
column isn't indexed, adding an index could significantly speed up your
UPDATE
queries and reduce the time locks are held. - Consider partitioning: If the
task_run
table is very large, you might want to consider partitioning it to improve performance. Remember, life is full of locks and keys. You just need to find the right key to unlock your problem. And if you can't, well, there's always the option of kicking the door down. But let's try the keys first, shall we?