PostgreSQL 9.5.
A very small update SQL uses very high CPU for a long time like a hang.
My Windows console application uses a simple UPDATE statement to update the latest time as follows.
UPDATE META_TABLE SET latest_time = current_timestamp WHERE host = 'MY_HOST'
There are just 2 console applications which issue above SQL.
No index on META_TABLE.
Only 1 row.
When it is hanging, no lock information.
UNLOGGED Table.
IDLE status in pg_stat_activity
Commit after UPDATE.
During that the hang time, I can INSERT or DELETE data with the table above.
After starting the application, about in 20 minutes, this issue happens.
I think it is not a SQL statement or table structure issue, probably something wrong in a database side.
Can you guess anything to resolve this issue?
Update
There are 2 db connections in the console application. 1 for Select & 1 for DML.
I tried to close DML DB connection every 2 minutes. Then, I haven't seen the issue!! However, the hang issue happened on SELECT statement (also very simple SELECT).
It seems that there is a some limit per the session.
Now, I am also closing the Select db connection as well per 3 minutes and monitoring.
Related
I'm doing a huge upgrade on a Database. I have quite a complex query that needs a few hours to run - I tested it on some sample data and the query is fine.
After analyzing my queries, I saw that my query changed from state 'ACTIVE' to 'IDLE' after running for 3:30h.
What does that exactly mean? The PostgreSQL manual indicates that this means the transaction is open (inside BEGIN) and idle. I
Will my query end? Should I kill it and find a smarter way to upgrade?
I have a table with 500k elements. Now I want to add a new column
(type boolean, nullable = false) without a default value.
The query to do so is running like for ever.
I'm using PostgreSQL 12.1, compiled by Visual C++ build 1914, 64-bit on my Windows 2012 Server
In pgAdmin I can see the query is blocked by PID 0. But when I execute this query, I can't see the query with pid = 0
SELECT *
FROM pg_stat_activity
Can someone help me here? Why is the query blocked and how can I fix this to add a new column to my table.
UPDATE attempt:
SELECT *
FROM pg_prepared_xacts
Update
It works after rollback all prepared transaction.
ROLLBACK PREPARED 'gid goes here';
You have got stale prepared transactions. I say that as in "you have got the measles", because it is a disease for a database.
Such prepared transactions keep holding locks and block autovacuum progress, so they will bring your database to its knees if you don't take action. In addition, such transactions are persisted, so even a restart of the database won't get rid of them.
Remove them with
ROLLBACK PREPARED 'gid goes here'; /* use the transaction names shown in the view */
If you use prepared transactions, you need a distributed transaction manager. That is a piece of software that keeps track of all prepared transactions and their state and persists that information, so that no distributed transaction can become stale. Even if there is a crash, the distributed transaction manager will resolve in-doubt transactions in all involved databases.
If you don't have that, don't use prepared transactions. You now know why. Best is to set max_prepared_transactions to 0 in that case.
I have pgpool installed on my server but I am facing issue while optimising it. I have 2 different queries running on the same table-
1st is update query which runs every 1 min and query exec time is around 30 secs. So technically it is running every 30 secs.
2nd is select query.
The issue I am facing here is that update query is running and i try to run select query , my pg-pool process only update query and until unless update query is not finished it wont process my select query.
As of now, I am following the pg-pool default settings.
Any kind of feedback will be helpful:
I am facing an issue, possibly quite easy to solve, I am just new to advanced transaction settings.
Every 30 minutes I am running an INSERT query that is getting latest data from a linked server to my client's server, to a table we can call ImportTable. For this I have a simple job that looks like this:
BEGIN TRAN
DELETE FROM ImportTable
INSERT INTO ImportTable (columns)
SELECT (columns)
FROM QueryGettingResultsFromLinkedServer
COMMIT
The thing is, each time the job runs the ImportTable is locked for the query run time (2-5 minutes) and nobody can read the records. I wish the table to be read-accessible all the time, with as little downtime as possible.
Now, I read that it is possible to allow SNAPSHOT ISOLATION in the database settings that could probably solve my problem (set to FALSE at the moment), but I have never played with different transaction isolation types and as this is not my DB but my client's, I'd rather not alter any database settings if I am not sure if it can break something.
I know I could have an intermediary table that the records are inserted to and then inserted to the final table and that is certainly a possible solution, I was just hoping for something more sophisticated and learning something new in the process.
PS: My client's server & database is fairly new and barely used, so I expect very little impact if I change some settings, but still, I cannot just randomly change various settings for learning purposes.
Many thanks!
Inserts wont normally block the table ,unless it is escalated to table level.In this case,you are deleting table first and inserting data again,why not insert only updated data?.for the query you are using transaction level (rsci)snapshot isolation will help you,but you will have an added impact of row version which means sql will store row versions of rows that changed in tempdb.
please see MCM isolation videos of Kimberely tripp for indepth understanding ,also dont forget to test in stage enviornment.
You are making this harder than it needs to be
The problem is the 2-5 minutes that you let be part of a transaction
It is only a few thousand rows - that part takes like a few milliseconds
If you need ImportTable to be available during those few milliseconds then put it in a SnapShot
Delete ImportTableStaging;
INSERT INTO ImportTableStaging(columns)
SELECT (columns)
FROM QueryGettingResultsFromLinkedServer;
BEGIN TRAN
DELETE FROM ImportTable
INSERT INTO ImportTable (columns) with (tablock)
SELECT (columns)
FROM ImportTableStaging
COMMIT
If you are worried about concurrent update to ImportTableStaging then use a #temp
All,
SQL 2005 sp3, database is about 70gb in size. Once in a while when I reindex all of my indexes in all of my tables, the front end seems to freeze up or run very slowly. These are queries coming from the front end, not stored procedures in sql server. The front end is using JTDS JDBC connection to access the SQL Server. If we stop and restart the web services sending the queries the problem seems to go away. It is my understandning that we have a connection pool in which we re-use connections and dont establish a new connection each time.
This problem does not happen every time we reindex. I have tried both ways with dbcc dbreindex and alter index online = on and sort in tempdb = on.
Any insight into why this problem occurs once in a while and how to prevent this problem would be very helpful.
Thanks in advance,
Gary Abbott
When this happens next time, look into sys.dm_exec_requests to see what is blocking the requests from the clients. The blocking_session_id will indicate who is blocking, and the wait_type and wait_resource will indicate what is blocking on. You can also use the Activity Monitor to the same effect.
On a pre-grown database an online index rebuild will not block normal activity 9select/insert/update/delete). The load on the server may increase as a result of the online index rebuild and this could result in overall slower responses, but should not cause blocking.
If the database is not pre-grown though then the extra allocations of the index rebuild will trigger database growth events, which can be very slow if left default at 10% increments and without instant file initialisation enabled. During a database growth event all activity is frozen in that database, and this may be your problem even if the indexes are rebuilt online. Again, Activity Monitor and sys.dm_exec_requests would both clearly show this as happening.