---
title: "Fixing Database Write errors"
url: https://phatdev.net/en/docs/sl-migrations/how-to-fix-database-write-issues
lang: en
updated: 2026-10-20
alternate:
  vi: https://phatdev.net/docs/sl-migrations/how-to-fix-database-write-issues
markdown: https://phatdev.net/en/docs/sl-migrations/how-to-fix-database-write-issues.md
---

# Fixing Database Write errors

Part of the doc set: [SL Migrations](https://phatdev.net/en/docs/sl-migrations.md)

> The database build phase or restore step 2 reports a write error.

## Database Write Issues

Symptoms:
- The database build phase fails with `ER_LOCK_WAIT_TIMEOUT`
- Restore step 2 reports `MySQL server has gone away`
- `max_allowed_packet too small`
- `Got a packet bigger than 'max_allowed_packet' bytes`

## Fix 1: max_allowed_packet

Restoring a large SQL dump needs a large enough `max_allowed_packet`.

Raise this value in the MySQL configuration. On shared hosting, contact support to have it raised. On a VPS, edit `my.cnf` or `mariadb.conf`:

```
[mysqld]
max_allowed_packet = 256M
```

Then restart MySQL/MariaDB.

## Fix 2: MySQL user is missing privileges

The restore user needs `ALL PRIVILEGES` on the database (including CREATE, DROP, INSERT, UPDATE, DELETE, INDEX, REFERENCES, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES, TRIGGER, EVENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE).

```sql
GRANT ALL PRIVILEGES ON example_db.* TO 'example_user'@'localhost';
FLUSH PRIVILEGES;
```

## Fix 3: Disk full

The database server cannot write when the disk is full. Check the free disk space on the server and delete old logs and unneeded binary logs (`PURGE BINARY LOGS`).

## Fix 4: MySQL crashed / connection drop

Restart the MySQL service. Check the MySQL/MariaDB error log to find the cause of the crash.

## Fix 5: innodb_lock_wait_timeout

A large restore needs a longer timeout:

```
[mysqld]
innodb_lock_wait_timeout = 600
```

## Fix 6: utf8mb4 collation mismatch

The error `Unknown collation: 'utf8mb4_0900_ai_ci'` when restoring a database from MySQL 8 to an older MariaDB.

**Fix 1**: replace the collation in the SQL file before importing:

```
sed -i 's/utf8mb4_0900_ai_ci/utf8mb4_unicode_ci/g' dump.sql
```

**Fix 2**: create the destination database with a compatible collation:

```sql
CREATE DATABASE example_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
```

## See also

- [Database Install](https://phatdev.net/en/docs/sl-migrations/database-install)
- [Server resources](https://phatdev.net/en/docs/sl-migrations/how-to-manage-server-resources-cpu-memory-disk)