Managing Extensions

Viewing Installed Extensions

Query installed extensions using the INFORMATION_SCHEMA view:

SELECT * FROM INFORMATION_SCHEMA.EXTENSIONS;

Output:

+------------------+-------------------+
| EXTENSION_NAME   | EXTENSION_VERSION |
+------------------+-------------------+
| vsql_complex     | 0.0.1             |
| vsql_uuid        | 0.0.3             |
+------------------+-------------------+

Usage:

Use in both interactive sessions and scripts
Standard SQL interface compatible with MySQL tools

Checking Extension Functions

Verify extension functions work after installation:

-- Test a function directly
SELECT complex_abs('(1.0,2.0)');

Extension Directory

Check where VillageSQL looks for .veb files:

SHOW VARIABLES LIKE 'veb_dir';

List available extensions:

ls -la /path/to/veb_dir/*.veb

Configuring veb_dir

To change the extension directory location, set veb_dir in your MySQL configuration file: my.cnf / my.ini:

[mysqld]
veb_dir=/custom/path/to/extensions/

Requirements:

Path must be absolute (not relative)
Directory must exist before server start
MySQL user must have read permissions on the directory
Only one veb_dir is supported (cannot have multiple paths)
Changes require server restart to take effect

Verify after restart:

SHOW VARIABLES LIKE 'veb_dir';

Troubleshooting

Quick Reference

Issue	Quick Fix
Extension not found	Verify `.veb` file exists in veb_dir with correct name
Permission denied	Check permissions: `chmod 644 extension.veb`
Cannot uninstall: types in use	Attempt `UNINSTALL EXTENSION`; the error identifies blocking columns by name
Version mismatch	Restart server to clear cache
Extension shows old behavior after update	`UNINSTALL` then `INSTALL`; clear `.veb_expansion_cache/` if needed
Cannot compare types X and Y	Both sides must use the same custom type
Unable to implicitly cast non-custom type	The literal or column being compared is not compatible with the custom type

Extension Not Found

Error: Extension 'my_extension' not found Debug steps:

# 1. Check veb_dir location
mysql -u root -p -e "SHOW VARIABLES LIKE 'veb_dir';"

# 2. List .veb files
ls -la /path/to/veb_dir/

# 3. Verify filename matches extension name
# File: my_extension.veb
# Install: INSTALL EXTENSION my_extension;

# 4. Check permissions
ls -l /path/to/veb_dir/my_extension.veb
sudo chmod 644 /path/to/veb_dir/my_extension.veb

Function Not Available After Install

Error: FUNCTION my_func does not exist Debug steps:

-- 1. Verify extension installed
SELECT * FROM INFORMATION_SCHEMA.EXTENSIONS WHERE EXTENSION_NAME = 'my_extension';

Extension Shows Old Behavior After Update

Symptom: After replacing a .veb file and reinstalling, the extension still runs old code. Cause: VillageSQL expands .veb files into {datadir}/.veb_expansion_cache/ on first load. If you copy a new .veb without first running UNINSTALL EXTENSION, the server continues using the previously-expanded .so that is already loaded in memory. Solution: Always follow the full UNINSTALL → replace → INSTALL cycle:

UNINSTALL EXTENSION my_extension;

Then replace the .veb file in veb_dir and reinstall:

INSTALL EXTENSION my_extension;

If the extension still shows old behavior, clear the expansion cache before reinstalling:

rm -rf {datadir}/.veb_expansion_cache/my_extension/

INSTALL EXTENSION my_extension;

Cannot Uninstall Extension

Error: Cannot uninstall extension: types in use Solution:

-- Attempt uninstall; the error identifies blocking columns by name
UNINSTALL EXTENSION my_extension;
-- If blocked: ERROR HY000: Cannot drop extension `my_extension` as 1 column(s) depend on it,
--             e.g. mydb.mytable.my_column has type MYTYPE

-- Drop or alter the identified column(s), then retry
DROP TABLE mydb.mytable;
-- OR
ALTER TABLE mydb.mytable DROP COLUMN my_column;

UNINSTALL EXTENSION my_extension;

Library Loading Errors

Error: Cannot load library: undefined symbol Causes:

Missing library dependencies
ABI compatibility mismatch
Incorrect MySQL version

Debug:

# Check library dependencies (Linux)
ldd {datadir}/.veb_expansion_cache/my_extension/<sha256>/lib/my_extension.so

# Check library dependencies (macOS)
otool -L {datadir}/.veb_expansion_cache/my_extension/<sha256>/lib/my_extension.so

Extension Name Validation Errors

Error: Failed to load VEF extension 'extension_name' with log message Extension name mismatch Cause: The extension name in manifest.json doesn’t match the VEB filename. Debug steps:

Check VEB filename matches manifest:

# VEB filename: my_extension.veb
# manifest.json should have:
{
  "name": "my_extension",  # Must match VEB filename (without .veb)
  ...
}

Verify manifest.json name field:

# Extract and check manifest from VEB
tar -xOf /path/to/veb_dir/my_extension.veb manifest.json | grep name

Solution: Both names must be identical, using underscores (see Extension Naming Conventions):

VEB filename: my_extension.veb
manifest.json: "name": "my_extension"

Common mistakes:

Using hyphens in manifest: "name": "my-extension" ❌
VEB filename doesn’t match: my-extension.veb vs "name": "my_extension" ❌

Correct example:

// manifest.json
{
  "name": "my_extension",
  "version": "1.0.0"
}

// extension.cc
VEF_GENERATE_ENTRY_POINTS(
  make_extension()
    .func(...)
)

# VEB filename
my_extension.veb

Custom Type Comparison Errors

Error: Cannot compare types X and Y in = Cause: Both sides of the comparison are custom types but from different types or extensions.

-- Example: comparing COMPLEX with UUID in a WHERE clause
SELECT * FROM t WHERE complex_col = uuid_col;
-- ERROR: Cannot compare types vsql_complex.COMPLEX and vsql_uuid.UUID in =

Solution: Ensure both sides of a comparison use the same custom type. If you need to compare across types, convert one side explicitly using the appropriate type conversion function.

Error: Unable to implicitly cast a non-custom type during compare with a custom type in = Cause: One side of the comparison is a custom type column and the other is a value (literal or column) that cannot be automatically converted to that type.

-- Example: comparing a custom type with an integer literal
SELECT * FROM t WHERE complex_col = 42;
-- ERROR: Unable to implicitly cast a non-custom type during compare...

Solution: String literals are automatically cast to the custom type using the type’s encode function. For other types (integers, floats), use an explicit conversion function:

-- Use a string literal instead (auto-cast works)
SELECT * FROM t WHERE complex_col = '(1.0,2.0)';

-- Or use the type's from_string method explicitly
SELECT * FROM t WHERE complex_col = COMPLEX::from_string('(1.0,2.0)');

Monitoring Extension Usage

Query Performance

Track VDF execution times using performance_schema:

-- Enable statement instrumentation
UPDATE performance_schema.setup_instruments
SET ENABLED = 'YES', TIMED = 'YES'
WHERE NAME LIKE '%statement%';

-- Query VDF execution times
SELECT
    DIGEST_TEXT,
    COUNT_STAR as executions,
    ROUND(SUM_TIMER_WAIT/1000000000, 2) as total_ms,
    ROUND(AVG_TIMER_WAIT/1000000000, 2) as avg_ms
FROM performance_schema.events_statements_summary_by_digest
WHERE DIGEST_TEXT LIKE '%complex_%'
ORDER BY total_ms DESC
LIMIT 10;

Custom Type Usage

Track which tables use custom types:

-- Find all columns using custom extension types
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE '%.%'
ORDER BY DATA_TYPE, TABLE_SCHEMA, TABLE_NAME;

Updating Extensions

To change an installed extension to a different version, use ALTER EXTENSION. It validates the new version against your existing data and applies the change the next time the server restarts. A manual uninstall and reinstall remains available as an alternative.

Changing an Extension Version

ALTER EXTENSION changes an installed extension to a different version, applied at the next server restart:

ALTER EXTENSION update_test VERSION '1.2.0' AT RESTART;

VillageSQL resolves the target version on disk and runs a compatibility precheck before accepting the change. The target VEB must exist in the extension directory as <name>-<version>.veb (here, update_test-1.2.0.veb); a missing file is rejected:

ERROR 3219 (HY000): VEB file not found: update_test-9.9.9.veb

The precheck looks for known incompatibilities that would break stored data — for example a change to a custom type’s persisted length:

ERROR 3219 (HY000): Cannot update extension 'update_test': type 'COUNTER'
persisted_length changed from 4 to 8 -- existing stored data would be corrupted

Once accepted, the change applies at the next restart. Until then, INFORMATION_SCHEMA.EXTENSIONS reports the current version alongside the target it will change to:

SELECT EXTENSION_NAME, EXTENSION_VERSION, PENDING_VERSION
FROM INFORMATION_SCHEMA.EXTENSIONS
WHERE EXTENSION_NAME = 'update_test';

+----------------+-------------------+-----------------+
| EXTENSION_NAME | EXTENSION_VERSION | PENDING_VERSION |
+----------------+-------------------+-----------------+
| update_test    | 1.0.0             | 1.2.0           |
+----------------+-------------------+-----------------+

INFORMATION_SCHEMA.EXTENSIONS reports a scheduled change in four columns:

Column	Meaning
`PENDING_VERSION`	Version the extension will change to at the next restart, or `NULL`
`PENDING_REQUESTED_AT`	When the change was requested
`PENDING_LAST_ERROR`	Message from a failed change, or `NULL`
`PENDING_LAST_ERROR_AT`	When that failure was recorded, or `NULL`

One scheduled change is tracked at a time:

Cancel a scheduled change by requesting the current version again:

ALTER EXTENSION update_test VERSION '1.0.0' AT RESTART;
-- Note: Cleared pending update for extension 'update_test'
--       (target matches current version '1.0.0')

Requesting the current version when nothing is scheduled does nothing:

ALTER EXTENSION update_test VERSION '1.0.0' AT RESTART;
-- Note: Extension 'update_test' is already at version '1.0.0'

A different target is refused while a change is scheduled — cancel the existing one first:

ERROR 3219 (HY000): Extension 'update_test' already has a pending update;
clear it with ALTER EXTENSION update_test VERSION '1.0.0' AT RESTART before
queueing a different version

The AT RESTART clause applies the change during the next server startup.

After a Successful Restart

On the next restart the pending change applies: EXTENSION_VERSION becomes the target and PENDING_VERSION clears. For the change scheduled above (update_test 1.0.0 → pending 1.2.0):

SELECT EXTENSION_NAME, EXTENSION_VERSION, PENDING_VERSION
FROM INFORMATION_SCHEMA.EXTENSIONS
WHERE EXTENSION_NAME = 'update_test';

+----------------+-------------------+-----------------+
| EXTENSION_NAME | EXTENSION_VERSION | PENDING_VERSION |
+----------------+-------------------+-----------------+
| update_test    | 1.2.0             | NULL            |
+----------------+-------------------+-----------------+

Any custom_columns and stored-procedure-parameter rows referencing the old version are rewritten during the same restart, so dependent tables and routines keep working with no manual migration.

The change applies during restart, not on a live connection — the values above are the post-restart state.

Recovering from a Pending Version Change at Startup

A scheduled version change is applied during the next server startup. If a pending action can’t be applied, the server can fail to start while persisting its pending-update decisions. Use --villagesql-skip-extension-updates when a queued ALTER EXTENSION ... AT RESTART is blocking startup and you need the server up before you can clear it. --villagesql-skip-extension-updates is a mysqld startup flag. When set, the server bypasses processing of pending ALTER EXTENSION ... AT RESTART actions: each extension loads at its currently-installed version, and its pending action is left intact on disk. The flag mutates nothing itself — it only skips applying the pending actions for that one startup. When the flag is set and at least one extension has a pending action, the server logs a single warning at startup naming how many were bypassed:

--villagesql-skip-extension-updates is set: bypassing N pending extension update(s). Extensions load at their currently-installed version. Query INFORMATION_SCHEMA.EXTENSIONS to see the pending actions; clear each via ALTER EXTENSION <name> VERSION '<current>' AT RESTART, then restart without the flag.

Start the server with the flag

In production, pass it as a normal mysqld command-line option or add it under [mysqld] in my.cnf:

mysqld --villagesql-skip-extension-updates

In the dev harness, pass it through with --:

./villagesql start -- --villagesql-skip-extension-updates

Success signal: the server starts, and the error log contains the bypassing N pending extension update(s) warning shown above.

Identify the pending actions

SELECT EXTENSION_NAME, EXTENSION_VERSION, PENDING_VERSION, PENDING_LAST_ERROR
FROM INFORMATION_SCHEMA.EXTENSIONS
WHERE PENDING_VERSION IS NOT NULL;

+--------------+-------------------+-----------------+--------------------+
| EXTENSION_NAME | EXTENSION_VERSION | PENDING_VERSION | PENDING_LAST_ERROR |
+--------------+-------------------+-----------------+--------------------+
| my_extension   | 1.0.0             | 2.0.0           | NULL               |
+--------------+-------------------+-----------------+--------------------+

Success signal: each row’s PENDING_VERSION is the target you need to clear; PENDING_LAST_ERROR shows why it failed to apply.

Clear each pending action

For every extension returned above, request its current version to cancel the queued change (the cancel mechanism described under Changing an Extension Version):

ALTER EXTENSION my_extension VERSION '1.0.0' AT RESTART;

Success signal: a Cleared pending update for extension '<name>' (target matches current version '<current>') note is returned, and re-running the previous query shows PENDING_VERSION is NULL.

Restart without the flag

Restart the server normally, omitting --villagesql-skip-extension-updates.Success signal: the server starts and the bypassing N pending extension update(s) warning no longer appears in the log.

Manual Update Process

Uninstall the current version:
UNINSTALL EXTENSION extension_name;

Replace the .veb file:

# Remove old .veb file
sudo rm /path/to/veb_dir/extension_name.veb

# Copy new .veb file
sudo cp new_extension_name.veb /path/to/veb_dir/

Install the new version:
INSTALL EXTENSION extension_name;

Verify the update:

SELECT EXTENSION_VERSION
FROM INFORMATION_SCHEMA.EXTENSIONS
WHERE EXTENSION_NAME = 'extension_name';

Data Safety: If tables use custom types from the extension, you must drop or alter those tables before uninstalling. Back up your data first.

Example:

-- Find columns using vsql_complex types before updating
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE LIKE 'vsql_complex.%';

-- If columns exist, back up data and drop/alter them first
-- Then proceed with update
UNINSTALL EXTENSION vsql_complex;
-- (replace .veb file)
INSTALL EXTENSION vsql_complex;

Cleaning Up

Remove Orphaned Expansion Directories

VillageSQL expands .veb files to {datadir}/.veb_expansion_cache/{name}/{sha256}/. Old versions accumulate over time.

# List expansion directories (replace {datadir} with your actual datadir path)
ls -la {datadir}/.veb_expansion_cache/

# Compare with installed extensions
mysql -u root -p -e "SELECT EXTENSION_NAME FROM INFORMATION_SCHEMA.EXTENSIONS;"

# Find the actual SHA256 directory name for a specific extension
ls {datadir}/.veb_expansion_cache/my_extension/

# Remove the unused SHA256 directory using the name shown above
rm -rf {datadir}/.veb_expansion_cache/my_extension/<sha256-from-ls>/

Server restart automatically cleans up orphaned expansion directories.

Replication

Custom types require ROW format binlog. STATEMENT and MIXED modes are not supported for tables with custom type columns. INSERT, UPDATE, DELETE, and ALTER TABLE operations on custom type columns all replicate correctly in ROW format. INSTALL EXTENSION is not replicated — each server manages its own extensions. Install the extension on every replica before replication starts, using the same version as the source. The server enforces exact version matching; a version mismatch stops replication. If a replica encounters a custom type it doesn’t recognize, replication stops at the DDL statement — on CREATE TABLE or ALTER TABLE, before any dependent DML is applied. Install the correct extension version, then resume:

INSTALL EXTENSION my_extension;
START REPLICA SQL_THREAD;

mysqldump preserves fully qualified custom type names in the output. Logical restores work as long as the extension is installed on the target server before importing the dump.

Behavior with the Clone plugin, XtraBackup, and InnoDB Cluster / Group Replication is not yet tested. Test your restore path before relying on it in production.

Using Extensions with Docker

When running VillageSQL in Docker, mount a local directory as veb_dir so you can add .veb files from the host without rebuilding the container. Docker Compose example:

services:
  villagesql:
    image: villagesql/server:stable
    environment:
      MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
    ports:
      - "3306:3306"
    volumes:
      - ./extensions:/usr/lib/veb
    command: --veb_dir=/usr/lib/veb

Copy a .veb file into ./extensions/ on the host, then install from SQL:

INSTALL EXTENSION my_extension;

To verify the directory the running server is using:

SHOW VARIABLES LIKE 'veb_dir';

Getting Help

If you encounter issues not covered here:

Check Error Log: Most extension errors are logged with details
Review Extension Docs: Extension-specific troubleshooting may exist
Ask on Discord: Join the VillageSQL Discord
File an Issue: Report bugs on GitHub Issues

Next Steps

System Reference

Query system tables and views

Uninstall Extensions

Remove extensions safely

Extension Architecture

Understand the internals

Getting Started

Server Development

Extensions

Using Extensions

Creating Extensions

Viewing Installed Extensions

Checking Extension Functions

Extension Directory

Configuring veb_dir

Troubleshooting

Quick Reference

Extension Not Found

Function Not Available After Install

Extension Shows Old Behavior After Update

Cannot Uninstall Extension

Library Loading Errors

Extension Name Validation Errors

Custom Type Comparison Errors

Monitoring Extension Usage

Query Performance

Custom Type Usage

Updating Extensions

Changing an Extension Version

After a Successful Restart

Recovering from a Pending Version Change at Startup

Manual Update Process

Cleaning Up

Remove Orphaned Expansion Directories

Replication

Using Extensions with Docker

Getting Help

Next Steps

System Reference

Uninstall Extensions

Extension Architecture

​Viewing Installed Extensions

​Checking Extension Functions

​Extension Directory

​Configuring veb_dir

​Troubleshooting

​Quick Reference

​Extension Not Found

​Function Not Available After Install

​Extension Shows Old Behavior After Update

​Cannot Uninstall Extension

​Library Loading Errors

​Extension Name Validation Errors

​Custom Type Comparison Errors

​Monitoring Extension Usage

​Query Performance

​Custom Type Usage

​Updating Extensions

​Changing an Extension Version

​After a Successful Restart

​Recovering from a Pending Version Change at Startup

​Manual Update Process

​Cleaning Up

​Remove Orphaned Expansion Directories

​Replication

​Using Extensions with Docker

​Getting Help

​Next Steps

System Reference

Uninstall Extensions

Extension Architecture

Viewing Installed Extensions

Checking Extension Functions

Extension Directory

Configuring veb_dir

Troubleshooting

Quick Reference

Extension Not Found

Function Not Available After Install

Extension Shows Old Behavior After Update

Cannot Uninstall Extension

Library Loading Errors

Extension Name Validation Errors

Custom Type Comparison Errors

Monitoring Extension Usage

Query Performance

Custom Type Usage

Updating Extensions

Changing an Extension Version

After a Successful Restart

Recovering from a Pending Version Change at Startup

Manual Update Process

Cleaning Up

Remove Orphaned Expansion Directories

Replication

Using Extensions with Docker

Getting Help

Next Steps