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ALTER SYSTEM is available in SDK v5+.
The ALTER SYSTEM statement provides runtime configuration management, allowing you to change system parameters dynamically.

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Syntax

DQL
ALTER SYSTEM SET parameter_name TO value
ALTER SYSTEM SET parameter_name = value
ALTER SYSTEM RESET parameter_name
ALTER SYSTEM RESET ALL
ALTER SYSTEM Syntax Diagram

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SET Parameter

Change a configuration parameter to a specific value:
DQL
-- Using TO syntax
ALTER SYSTEM SET DQL_STRICT_MODE TO false

-- Using = syntax (equivalent)
ALTER SYSTEM SET DQL_STRICT_MODE = false

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Set to DEFAULT

Reset a parameter to its default value using the DEFAULT keyword:
DQL
ALTER SYSTEM SET parameter_name TO DEFAULT

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RESET Parameter

Reset a configuration parameter to its default value:
DQL
-- Reset single parameter
ALTER SYSTEM RESET DQL_STRICT_MODE

-- Reset all parameters to defaults
ALTER SYSTEM RESET ALL

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Parameter Values

Parameter values can be:
  • Literals: Numbers, strings, booleans
    • Boolean: true, false
    • Integer: 100, 5000
    • String: 'value' or "value"
  • DEFAULT keyword: Resets to the default value

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Available DQL Configuration Parameters

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DQL_STRICT_MODE

Type: Boolean Default: true Controls whether strict mode is enabled for collection type definitions.
DQL
ALTER SYSTEM SET DQL_STRICT_MODE TO false
See Strict Mode for more information.

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DQL_DEFAULT_DIRECTIVES

Type: Object (JSON) Default: {} Sets default query directives that apply to all queries. Individual query directives can override these defaults.
DQL
-- Set default directives for development
ALTER SYSTEM SET DQL_DEFAULT_DIRECTIVES = {"#reprepare": true, "#max_serial_ranges": 2}

-- Reset to no default directives
ALTER SYSTEM SET DQL_DEFAULT_DIRECTIVES = {}
See Directives for more information.

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DQL_CONCURRENT_REQUEST_LIMIT

Type: Integer Default: System-dependent Limits the number of concurrent DQL requests that can execute simultaneously. When the limit is reached, additional requests are queued until capacity becomes available.
DQL
-- Limit to 10 concurrent requests
ALTER SYSTEM SET DQL_CONCURRENT_REQUEST_LIMIT TO 10

-- Reset to default (no limit)
ALTER SYSTEM RESET DQL_CONCURRENT_REQUEST_LIMIT
This parameter helps prevent resource exhaustion under heavy query load by controlling the maximum number of queries running at once.

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Available Transport Configuration Parameters

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tcp_server_bind_mdns_server_port

Type: Integer Default: Random port Specifies the port that a Small Peer SDK instance uses for mDNS announcements and incoming LAN (TCP) connections on the local device. Setting an explicit port is useful when you need to traverse a VLAN or firewall by scanning for open ports, or when you need a deterministic port for network policy. Leaving the parameter unset preserves the default behavior of binding to a random port.
DQL
ALTER SYSTEM SET tcp_server_bind_mdns_server_port TO 1234
If you run multiple Ditto applications on the same device — for example a debug or TestFlight build alongside a production build — each application must use a unique port. Otherwise only one application will be able to establish LAN connections at a time.
tcp_server_bind_mdns_server_port must be set before sync is started for the value to take effect.
let result = try await ditto.store.execute(
  query: "ALTER SYSTEM SET tcp_server_bind_mdns_server_port TO 1234"
)
See Local Area Network for the underlying mDNS, TCP, and firewall behavior this parameter affects.

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Common Use Cases

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Enable/Disable Strict Mode

DQL
-- Disable strict mode to allow flexible type definitions
ALTER SYSTEM SET DQL_STRICT_MODE TO false

-- Re-enable strict mode
ALTER SYSTEM SET DQL_STRICT_MODE TO true

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Configure Default Query Directives

DQL
-- Set default directives during development
ALTER SYSTEM SET DQL_DEFAULT_DIRECTIVES = {"#reprepare": true}

-- Clear default directives for production
ALTER SYSTEM SET DQL_DEFAULT_DIRECTIVES = {}

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Control Concurrent Query Execution

DQL
-- Limit concurrent queries to prevent overload
ALTER SYSTEM SET DQL_CONCURRENT_REQUEST_LIMIT TO 20

-- Remove limit
ALTER SYSTEM RESET DQL_CONCURRENT_REQUEST_LIMIT

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Reset All Configuration

DQL
-- Reset all parameters to their default values
ALTER SYSTEM RESET ALL

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Examples

// Set strict mode
await ditto.store.execute(
  query: "ALTER SYSTEM SET DQL_STRICT_MODE TO false"
)

// Reset parameter
await ditto.store.execute(
  query: "ALTER SYSTEM RESET DQL_STRICT_MODE"
)

// Reset all parameters
await ditto.store.execute(
  query: "ALTER SYSTEM RESET ALL"
)

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Checking Current Values

To verify the current value of a parameter after changing it, use the SHOW statement:
DQL
-- Set parameter
ALTER SYSTEM SET DQL_STRICT_MODE TO false

-- Verify the change
SHOW DQL_STRICT_MODE
Configuration changes made with ALTER SYSTEM are runtime only and do not persist across restarts. To apply settings on every startup, set the parameters in your Ditto instance configuration before starting.

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See Also

  • SHOW - Display configuration parameter values
  • Strict Mode - Understanding DQL_STRICT_MODE parameter