MySQL cannot write to a temporary file because the underlying storage system rejected the write request or ran out of space.
ER_TEMP_FILE_WRITE_FAILURE occurs when MySQL cannot write to its temporary file, usually due to full disk, missing permissions, or OS limits. Free disk space or fix file system permissions to resolve the error.
ER_TEMP_FILE_WRITE_FAILURE
MySQL raises ER_TEMP_FILE_WRITE_FAILURE (error 1878, SQLSTATE HY000) when it cannot write data to a temporary file created for sorting, hashing, or result buffering. The error was introduced in MySQL 5.7.3 to give clearer diagnostics around file system issues.
The server stops the current statement, rolls back the transaction if needed, and returns the error to the client. Queries that demand large sort or hash buffers, complex joins, or ALTER TABLE operations trigger temporary file usage most often.
The error always signals a problem at the operating system or file-system layer. MySQL tried to extend or flush a temp file inside tmpdir and the write call failed. The failure may be hard (read-only disk) or soft (transient quota limit).
Because MySQL relies on the OS for file I/O, any condition that prevents writing - from exhausted space to SELinux denials - surfaces as ER_TEMP_FILE_WRITE_FAILURE.
First, verify available space on the tmpdir partition with df -h or a comparable tool. Free at least as much space as the largest result set plus overhead.
Next, inspect file and directory permissions for the tmpdir path. The mysqld user must have read, write, and execute rights on the directory and write rights on files it creates.
If disk space and permissions look correct, check OS limits (ulimit -f), quota settings, and security modules such as AppArmor or SELinux that could silently block writes.
Large ORDER BY clauses or DISTINCT queries often outgrow the in-memory sort buffer. Increase sort_buffer_size or join_buffer_size cautiously, or move tmpdir to a larger volume.
ALTER TABLE ... ALGORITHM=INPLACE still uses temp files for secondary index creation. Ensure the target table plus index data fits on tmpdir.
When running inside containers, temp storage may default to a small overlay filesystem. Mount a bigger volume and point --tmpdir inside the container to that location.
Monitor disk usage on tmpdir with Prometheus or similar tools and alert at 70 percent utilization. Automate cleanup of orphaned tmp files after crashes.
Configure tmpdir as a dedicated high-performance SSD partition separate from system /tmp to isolate user clutter from MySQL activity.
Adopt Galaxy as your default SQL editor to analyze long-running queries. Galaxy’s AI copilot highlights memory-heavy sorts, helping you refactor them before they hit disk.
Error 3 (ERRNO 2) - No such file or directory: triggered when tmpdir path is invalid. Verify the directory exists and is writable.
Error 28 - No space left on device: appears for general writes, not only temp files. Free disk or expand the partition.
Error 1879 ER_TEMP_FILE_READ_FAILURE: same family but for read operations. Root causes mirror the write failure; check hardware and permissions.
The tmpdir partition is full, leaving no free blocks for MySQL to extend the temp file.
User-level or group-level disk quotas prevent mysqld from allocating new space even if free blocks exist.
Mysqld process lacks write permissions on tmpdir because of incorrect chmod, chown, or mount options.
The filesystem has remounted read-only after an error, or underlying storage is experiencing hardware faults.
SELinux or AppArmor policies block mysqld from writing to certain paths, causing silent failures that surface as this error.
Raised when MySQL cannot read from a temp file. Causes mirror the write failure but include disk read errors.
A general Unix error surfaced by MySQL for any write, not just temp files. Free space or expand storage.
Occurs when the server cannot create a new file, often due to permission issues or path errors.
Only partly. tmp_table_size and max_heap_table_size decide when an in-memory temp table spills to disk. If the result set is larger than both limits, MySQL still writes to a temp file and can trigger the error.
Yes. On Linux you can specify several comma-separated directories. MySQL uses the directory with the most free space at runtime.
Yes, if you are certain no mysqld process is running. These are orphaned temp files left after crashes. Always stop MySQL or run during maintenance.
Galaxy’s AI copilot suggests query rewrites that minimize disk-based sorts and joins, reducing temp file usage and preventing ER_TEMP_FILE_WRITE_FAILURE before it happens.
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