---
id: e1087707-ff0d-4b1c-9c0e-647b5a9695f2
---

# Concurrency issues with write operations in PostgreSQL.
---

Concurrency issues with write operations occur when multiple users or processes attempt to write to the same database at the same time, leading to race conditions and data inconsistencies. This can cause corruption of data, loss of data, or unexpected behavior in the database. It is important to handle concurrency issues properly to maintain data integrity and ensure that the database is functioning correctly.

### Parameters
```shell
export HOSTNAME="PLACEHOLDER"

export USERNAME="PLACEHOLDER"

export DATABASE_NAME="PLACEHOLDER"

export TABLE_NAME="PLACEHOLDER"

export ID_VALUE="PLACEHOLDER"

export DATABASE_PASSWORD="PLACEHOLDER"

export DATABASE_PORT="PLACEHOLDER"
```

## Debug

### Check the number of active connections to the database
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT count(*) FROM pg_stat_activity;"
```

### Check for long running transactions
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT pid, age(clock_timestamp(), query_start), usename, query FROM pg_stat_activity WHERE query NOT LIKE '%IDLE%' AND query NOT LIKE '%pg_stat_activity%' AND query NOT LIKE '%SELECT count(*)%' ORDER BY query_start ASC LIMIT 10;"
```

### Check for deadlocks
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT * FROM pg_locks WHERE NOT granted;"
```

### Check for table locks
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT * FROM pg_locks WHERE relation IS NOT NULL;"
```

### Check for blocked processes
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT block.pid AS blocked_pid, block.query AS blocked_query, block.mode AS blocked_mode, block.relation::regclass, now() - block.activity_age AS blocked_duration, blocker.pid AS blocking_pid, blocker.query AS blocking_query, blocker.mode AS blocking_mode, now() - blocker.activity_age AS blocking_duration FROM pg_catalog.pg_locks AS block JOIN pg_catalog.pg_locks AS blocker ON block.relation = blocker.relation AND block.pid != blocker.pid WHERE NOT block.granted;"
```

### Check for slow queries
```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT query, (now() - query_start) AS duration FROM pg_stat_activity WHERE state='active' AND now() - query_start > INTERVAL '1 minute';"
```

### Multiple users or processes are attempting to write to the same database table simultaneously.
```shell


#!/bin/bash



# Set variables

database=${DATABASE_NAME}

table=${TABLE_NAME}



# Check for active write operations

active_writes=$(psql -d $database -c "SELECT count(*) FROM pg_stat_activity WHERE query LIKE '%INSERT INTO $table%' OR query LIKE '%UPDATE $table%' OR query LIKE '%DELETE FROM $table%'")



# Check for locks on the table

table_locks=$(psql -d $database -c "SELECT count(*) FROM pg_locks WHERE relation::regclass = '$table'::regclass")



# Check for blocked processes

blocked_processes=$(psql -d $database -c "SELECT count(*) FROM pg_stat_activity WHERE waiting='t'")



# Output results

echo "Active write operations: $active_writes"

echo "Table locks: $table_locks"

echo "Blocked processes: $blocked_processes"


```

## Repair

### Use PostgreSQL's built-in locking mechanisms, such as row-level locks or advisory locks, to prevent multiple processes from writing to the same data at the same time.
```shell
bash

#!/bin/bash



# Define variables

database=${DATABASE_NAME}

table=${TABLE_NAME}

id=${ID_VALUE}



# Connect to PostgreSQL

psql -d $database -c "BEGIN; LOCK TABLE $table IN ROW EXCLUSIVE MODE; UPDATE $table SET column = value WHERE id = $id; COMMIT;"


```

Concurrency issues with write operations occur when multiple users or processes attempt to write to the same database at the same time, leading to race conditions and data inconsistencies. This can cause corruption of data, loss of data, or unexpected behavior in the database. It is important to handle concurrency issues properly to maintain data integrity and ensure that the database is functioning correctly.


```shell
export HOSTNAME="PLACEHOLDER"

export USERNAME="PLACEHOLDER"

export DATABASE_NAME="PLACEHOLDER"

export TABLE_NAME="PLACEHOLDER"

export ID_VALUE="PLACEHOLDER"

export DATABASE_PASSWORD="PLACEHOLDER"

export DATABASE_PORT="PLACEHOLDER"
```


### Check the number of active connections to the database

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT count(*) FROM pg_stat_activity;"
```

### Check for long running transactions

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT pid, age(clock_timestamp(), query_start), usename, query FROM pg_stat_activity WHERE query NOT LIKE '%IDLE%' AND query NOT LIKE '%pg_stat_activity%' AND query NOT LIKE '%SELECT count(*)%' ORDER BY query_start ASC LIMIT 10;"
```

### Check for deadlocks

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT * FROM pg_locks WHERE NOT granted;"
```

### Check for table locks

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT * FROM pg_locks WHERE relation IS NOT NULL;"
```

### Check for blocked processes

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT block.pid AS blocked_pid, block.query AS blocked_query, block.mode AS blocked_mode, block.relation::regclass, now() - block.activity_age AS blocked_duration, blocker.pid AS blocking_pid, blocker.query AS blocking_query, blocker.mode AS blocking_mode, now() - blocker.activity_age AS blocking_duration FROM pg_catalog.pg_locks AS block JOIN pg_catalog.pg_locks AS blocker ON block.relation = blocker.relation AND block.pid != blocker.pid WHERE NOT block.granted;"
```

### Check for slow queries

```shell
psql -U ${USERNAME} -h ${HOSTNAME} -c "SELECT query, (now() - query_start) AS duration FROM pg_stat_activity WHERE state='active' AND now() - query_start > INTERVAL '1 minute';"
```

### Multiple users or processes are attempting to write to the same database table simultaneously.

```shell


#!/bin/bash



# Set variables

database=${DATABASE_NAME}

table=${TABLE_NAME}



# Check for active write operations

active_writes=$(psql -d $database -c "SELECT count(*) FROM pg_stat_activity WHERE query LIKE '%INSERT INTO $table%' OR query LIKE '%UPDATE $table%' OR query LIKE '%DELETE FROM $table%'")



# Check for locks on the table

table_locks=$(psql -d $database -c "SELECT count(*) FROM pg_locks WHERE relation::regclass = '$table'::regclass")



# Check for blocked processes

blocked_processes=$(psql -d $database -c "SELECT count(*) FROM pg_stat_activity WHERE waiting='t'")



# Output results

echo "Active write operations: $active_writes"

echo "Table locks: $table_locks"

echo "Blocked processes: $blocked_processes"


```


### Use PostgreSQL's built-in locking mechanisms, such as row-level locks or advisory locks, to prevent multiple processes from writing to the same data at the same time.

```shell
bash

#!/bin/bash



# Define variables

database=${DATABASE_NAME}

table=${TABLE_NAME}

id=${ID_VALUE}



# Connect to PostgreSQL

psql -d $database -c "BEGIN; LOCK TABLE $table IN ROW EXCLUSIVE MODE; UPDATE $table SET column = value WHERE id = $id; COMMIT;"


```


Concurrency issues with write operations in PostgreSQL.

Overview

Parameters

Debug

Check the number of active connections to the database

Check for long running transactions

Check for deadlocks

Check for table locks

Check for blocked processes

Check for slow queries

Multiple users or processes are attempting to write to the same database table simultaneously.

Repair

Use PostgreSQL's built-in locking mechanisms, such as row-level locks or advisory locks, to prevent multiple processes from writing to the same data at the same time.

Learn more

Related Runbooks

Support