Hologres query management and timeout processing

adopt Hologres Of Query Management can query SQL Operation information of , Set up Query Timeout for running , Better management SQL, Prevent deadlock .

Inquire about pg_stat_activity View information

select * from pg_stat_activity ;

pg_stat_activity Parameter description of view ：

• datid：Hologres The database to which the backend is connected OID.
• datname：Hologres The name of the database to which the backend is connected .
• pid：Hologres Back end process ID.
• usesysid： Log in to Hologres Back end users OID.
• usename： The user name of the current connection .
• application_name： Application type of client .
• client_addr： Client's IP Address . According to the IP The address may be resolved , There is no guarantee that it must be the source IP.
• client_hostname： Host name of the client .
• client_port： Client port .
• backend_start： The time when the background process starts .
• xact_start： The time when the current transaction of the process was started .
  • If there are no active transactions , Is empty .
  • If the current query is the first transaction of the process , This column is equal to query_start.
• query_start： The time when the current active query started , If the current connection state is not active, The value is the start time of the previous query .
• state_change： The state of the connection （state） The last time it was changed .
• wait_event_type： The type of event the backend is waiting for , If it doesn't exist, it is NULL. The possible values are ：
  • LWLock： The backend is waiting for a lightweight lock .
  • Lock： The backend is waiting for a heavyweight lock .wait_event Will identify the type of lock waiting .
  • BufferPin： The server process is waiting to access a data buffer , At this time, no other process is checking the buffer .
  • Activity： The server process is idle . A system process used to wait for activity in its main processing loop .
  • Extension： The server process is waiting for activity in an extension module .
  • Client： The server process is waiting for some kind of query from the user application , And the server anticipates something that has nothing to do with its internal processing .
  • PC： The server process is waiting for some activity from another process in the server .
  • Timeout： The server process is waiting for a timeout to occur .
  • IO： The server process is waiting for one IO complete .
• wait_event： If the backend is currently waiting , Is the name of the waiting event , Otherwise NULL.
• state： Indicates the status of the connection . Common states are as follows ：
  • active： active .
  • idle： Free .
  • idle in transaction： Idle state in long transactions .
  • idle in transaction（Aborted）： Idle state in failed transactions .
  • \N: The state is empty , Represents a non user connected process , Generally, it belongs to the maintenance process in the background of the system , You can ignore .
• backend_xid：Hologres The top-level transaction identifier of the back end .
• backend_xmin： Current backend xmin Range .
• query： Recent queries executed by the backend . If state by active, The currently executing query will be displayed . In all other states , Display the last executed query .
• backend_type： Current backend type . Possible types are autovacuum launcher、autovacuum worker、logical replication launcher、logical replication worker、parallel worker、background writer、client backend、checkpointer、startup、walreceiver、walsender as well as walwriter. In addition, it also includes the back-end execution components , for example PQE etc. .

HoloWeb Active visualization Query management

Can pass HoloWeb Visual view active Query, And manage .

see SQL Operation information

Superuser You can view all users SQL Operation information ,RAM Users can only view their own SQL Operation information .

1. You can view the user's in the current instance through the following statement SQL Operation information .

SELECT datname::text,usename,query,pid::text,state FROM pg_stat_activity;

2. You can execute the following statement to view the currently running SQL Information .

SELECT datname::text,usename,query,pid::text,state
   FROM pg_stat_activity
   WHERE state != 'idle' ;

3. You can execute the following statement to view the current instance that is running and takes a long time SQL Information .

SELECT current_timestamp - query_start as runtime, datname::text, usename, query, pid::text
    FROM pg_stat_activity
    WHERE state != 'idle'
    order by 1 desc;

4. End Query

If there is currently something that does not meet expectations Query, The following commands can be used to terminate according to the actual situation .

Cancel Query.

select pg_cancel_backend(<pid>);

Batch cancel Query.

SELECT pg_cancel_backend(pid)
        ,query
        ,datname::text
        ,usename
        ,application_name
        ,client_addr
        ,client_port
        ,backend_start
        ,state
FROM    pg_stat_activity
WHERE   length(query) > 0
AND     pid != pg_backend_pid()
AND     backend_type = 'client backend'
AND     application_name != 'hologres'
AND     usename != 'holo_admin'
AND     query not like '%pg_cancel_backend%';

Modify active Query Timeout time

-- session  Level modification ( To modify the timeout SQL Statements are executed together to take effect )
set statement_timeout = <time>;
-- db  Level modification 
alter database dbname set statement_timeout=<time>;

time The value range of timeout is 0~2147483647ms, The default unit is ms（ When time You need to use single quotation marks when adding units , Otherwise, an error will be reported ）. The current default timeout is 8 Hours .

Examples are as follows ：

Set the timeout to 10min, The specific time zone unit ,10min You need to add single quotation marks as a whole .

set statement_timeout = '10min' ; 
select * from tablename;

Set the timeout to 5000ms.

set statement_timeout = 5000 ; 
select * from tablename;

Set up db The timeout is 10min.

alter database dbname set statement_timeout='10min';

Query whether the settings are effective ：

show statement_timeout;

Modify idle Query Timeout time

Parameters idle_in_transaction_session_timeout Describes the transaction entry idle Timeout behavior after status , If the parameter value is not set , By default, the transaction timeout will not be released , Transactions are prone to occur without releasing , Causes the query to be locked .

When Query When execution generates deadlock , You need to set the timeout . For example, the following code , unexecuted commit, Opened a transaction , But didn't submit , It will cause transaction leakage , And then cause database level deadlock , Affect the normal use of the service .

begin; 
select * from t;

When this deadlock scenario occurs , Can be set by idle_in_transaction_session_timeout Timeout to solve . When an idle connection with transactions exceeds idle_in_transaction_session_timeout The set time has not been committed or rolled back , The system will automatically rollback the transaction according to the timeout , And close the connection .

--session Modify idle transaction timeout 
set idle_in_transaction_session_timeout=<time>;

--DB Level modify idle transaction timeout 
alter database db_name set idle_in_transaction_session_timeout=<time>;

time The value range of timeout is 0~2147483647ms, The default unit is ms（ When time You need to use single quotation marks when adding units , Otherwise, an error will be reported ）. stay Hologres V0.10 Up to , The default value is 0, That is, it will not be cleaned automatically ; stay Hologres V1.1 edition , The default value is 10 minute , exceed 10 The transaction will be rolled back in minutes .

It is not recommended to set the timeout too short , If it is too short, it is easy to rollback the transaction in use .

Set the timeout to 300000ms.

--session Modify idle transaction timeout 
set idle_in_transaction_session_timeout=300000;

--DB Level modify idle transaction timeout 
alter database db_name set idle_in_transaction_session_timeout=300000;

Query whether the settings are effective ：

show idle_in_transaction_session_timeout;

reference ：https://help.aliyun.com/document_detail/263548.html