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1.0 (stable)
Pragmas

The PRAGMA statement is a SQL extension adopted by DuckDB from SQLite. PRAGMA statements can be issued in a similar manner to regular SQL statements. PRAGMA commands may alter the internal state of the database engine, and can influence the subsequent execution or behavior of the engine.

PRAGMA statements that assign a value to an option can also be issued using the SET statement and the value of an option can be retrieved using SELECT current_setting(option_name).

For DuckDB's built in configuration options, see the Configuration Reference. DuckDB extensions may register additional configuration options. These are documented in the respective extensions' documentation pages.

This page contains the supported PRAGMA settings.

Metadata

Schema Information

List all databases:

PRAGMA database_list;

List all tables:

PRAGMA show_tables;

List all tables, with extra information, similarly to DESCRIBE:

PRAGMA show_tables_expanded;

To list all functions:

PRAGMA functions;

Table Information

Get info for a specific table:

PRAGMA table_info('table_name');
CALL pragma_table_info('table_name');

table_info returns information about the columns of the table with name table_name. The exact format of the table returned is given below:

cid INTEGER,        -- cid of the column
name VARCHAR,       -- name of the column
type VARCHAR,       -- type of the column
notnull BOOLEAN,    -- if the column is marked as NOT NULL
dflt_value VARCHAR, -- default value of the column, or NULL if not specified
pk BOOLEAN          -- part of the primary key or not

To also show table structure, but in a slightly different format (included for compatibility):

PRAGMA show('table_name');

Database Size

Get the file and memory size of each database:

SET database_size;
CALL pragma_database_size();

database_size returns information about the file and memory size of each database. The column types of the returned results are given below:

database_name VARCHAR, -- database name
database_size VARCHAR, -- total block count times the block size
block_size BIGINT,     -- database block size
total_blocks BIGINT,   -- total blocks in the database
used_blocks BIGINT,    -- used blocks in the database
free_blocks BIGINT,    -- free blocks in the database
wal_size VARCHAR,      -- write ahead log size
memory_usage VARCHAR,  -- memory used by the database buffer manager
memory_limit VARCHAR   -- maximum memory allowed for the database

Storage Information

To get storage information:

PRAGMA storage_info('table_name');
CALL pragma_storage_info('table_name');

This call returns the following information for the given table:

Name Type Description
row_group_id BIGINT  
column_name VARCHAR  
column_id BIGINT  
column_path VARCHAR  
segment_id BIGINT  
segment_type VARCHAR  
start BIGINT The start row id of this chunk
count BIGINT The amount of entries in this storage chunk
compression VARCHAR Compression type used for this column – see blog post
stats VARCHAR  
has_updates BOOLEAN  
persistent BOOLEAN false if temporary table
block_id BIGINT empty unless persistent
block_offset BIGINT empty unless persistent

See Storage for more information.

Show Databases

The following statement is equivalent to the SHOW DATABASES statement:

PRAGMA show_databases;

Resource Management

Memory Limit

Set the memory limit for the buffer manager:

SET memory_limit = '1GB';
SET max_memory = '1GB';

Warning The specified memory limit is only applied to the buffer manager. For most queries, the buffer manager handles the majority of the data processed. However, certain in-memory data structures such as vectors and query results are allocated outside of the buffer manager. Additionally, aggregate functions with complex state (e.g., list, mode, quantile, string_agg, and approx functions) use memory outside of the buffer manager. Therefore, the actual memory consumption can be higher than the specified memory limit.

Threads

Set the amount of threads for parallel query execution:

SET threads = 4;

Collations

List all available collations:

PRAGMA collations;

Set the default collation to one of the available ones:

SET default_collation = 'nocase';

Default Ordering for NULLs

Set the default ordering for NULLs to be either NULLS FIRST or NULLS LAST:

SET default_null_order = 'NULLS FIRST';
SET default_null_order = 'NULLS LAST';

Set the default result set ordering direction to ASCENDING or DESCENDING:

SET default_order = 'ASCENDING';
SET default_order = 'DESCENDING';

Implicit Casting to VARCHAR

Prior to version 0.10.0, DuckDB would automatically allow any type to be implicitly cast to VARCHAR during function binding. As a result it was possible to e.g., compute the substring of an integer without using an explicit cast. For version v0.10.0 and later an explicit cast is needed instead. To revert to the old behaviour that performs implicit casting, set the old_implicit_casting variable to true:

SET old_implicit_casting = true;

Information on DuckDB

Version

Show DuckDB version:

PRAGMA version;
CALL pragma_version();

Platform

platform returns an identifier for the platform the current DuckDB executable has been compiled for, e.g., osx_arm64. The format of this identifier matches the platform name as described on the extension loading explainer:

PRAGMA platform;
CALL pragma_platform();

User Agent

The following statement returns the user agent information, e.g., duckdb/v0.10.0(osx_arm64):

PRAGMA user_agent;

Metadata Information

The following statement returns information on the metadata store (block_id, total_blocks, free_blocks, and free_list):

PRAGMA metadata_info;

Progress Bar

Show progress bar when running queries:

PRAGMA enable_progress_bar;

Or:

PRAGMA enable_print_progress_bar;

Don't show a progress bar for running queries:

PRAGMA disable_progress_bar;

Or:

PRAGMA disable_print_progress_bar;

Profiling Queries

Explain Plan Output

The output of EXPLAIN output can be configured to show only the physical plan. This is the default configuration:

SET explain_output = 'physical_only';

To only show the optimized query plan:

SET explain_output = 'optimized_only';

To show all query plans:

SET explain_output = 'all';

Profiling

Enable Profiling

To enable profiling:

PRAGMA enable_profiling;

Or:

PRAGMA enable_profile;

Profiling Format

The format of the resulting profiling information can be specified as either json, query_tree, or query_tree_optimizer. The default format is query_tree, which prints the physical operator tree together with the timings and cardinalities of each operator in the tree to the screen.

To return the logical query plan as JSON:

SET enable_profiling = 'json';

To return the logical query plan:

SET enable_profiling = 'query_tree';

To return the physical query plan:

SET enable_profiling = 'query_tree_optimizer';

Disable Profiling

To disable profiling:

PRAGMA disable_profiling;

Or:

PRAGMA disable_profile;

Profiling Output

By default, profiling information is printed to the console. However, if you prefer to write the profiling information to a file the PRAGMA profiling_output can be used to write to a specified file.

Warning The file contents will be overwritten for every new query that is issued, hence the file will only contain the profiling information of the last query that is run:

SET profiling_output = '/path/to/file.json';
SET profile_output = '/path/to/file.json';

Profiling Mode

By default, a limited amount of profiling information is provided (standard). For more details, use the detailed profiling mode by setting profiling_mode to detailed. The output of this mode shows how long it takes to apply certain optimizers on the query tree and how long physical planning takes:

SET profiling_mode = 'detailed';

Query Optimization

Optimizer

To disable the query optimizer:

PRAGMA disable_optimizer;

To enable the query optimizer:

PRAGMA enable_optimizer;

Selectively Disabling Optimizers

The disabled_optimizers option allows selectively disabling optimization steps. For example, to disable filter_pushdown and statistics_propagation, run:

SET disabled_optimizers = 'filter_pushdown,statistics_propagation';

The available optimizations can be queried using the duckdb_optimizers() table function.

Warning The disabled_optimizers option should only be used for debugging performance issues and should be avoided in production.

Logging

Set a path for query logging:

SET log_query_path = '/tmp/duckdb_log/';

Disable query logging:

SET log_query_path = '';

Full-Text Search Indexes

The create_fts_index and drop_fts_index options are only available when the fts extension is loaded. Their usage is documented on the Full-Text Search extension page.

Verification

Verification of External Operators

Enable verification of external operators:

PRAGMA verify_external;

Disable verification of external operators:

PRAGMA disable_verify_external;

Verification of Round-Trip Capabilities

Enable verification of round-trip capabilities for supported logical plans:

PRAGMA verify_serializer;

Disable verification of round-trip capabilities:

PRAGMA disable_verify_serializer;

Object Cache

Enable caching of objects for e.g., Parquet metadata:

PRAGMA enable_object_cache;

Disable caching of objects:

PRAGMA disable_object_cache;

Checkpointing

Force Checkpoint

When CHECKPOINT is called when no changes are made, force a checkpoint regardless:

PRAGMA force_checkpoint;

Checkpoint on Shutdown

Run a CHECKPOINT on successful shutdown and delete the WAL, to leave only a single database file behind:

PRAGMA enable_checkpoint_on_shutdown;

Don't run a CHECKPOINT on shutdown:

PRAGMA disable_checkpoint_on_shutdown;

Temp Directory for Spilling Data to Disk

By default, DuckDB uses a temporary directory named ⟨database_file_name⟩.tmp to spill to disk, located in the same directory as the database file. To change this, use:

SET temp_directory = '/path/to/temp_dir.tmp/';

Returning Errors as JSON

The errors_as_json option can be set to obtain error information in raw JSON format. For certain errors, extra information or decomposed information is provided for easier machine processing. For example:

SET errors_as_json = true;

Then, running a query that results in an error produces a JSON output:

SELECT * FROM nonexistent_tbl;
{
   "exception_type":"Catalog",
   "exception_message":"Table with name nonexistent_tbl does not exist!\nDid you mean \"temp.information_schema.tables\"?",
   "name":"nonexistent_tbl",
   "candidates":"temp.information_schema.tables",
   "position":"14",
   "type":"Table",
   "error_subtype":"MISSING_ENTRY"
}

Query Verification (for Development)

The following PRAGMAs are mostly used for development and internal testing.

Enable query verification:

PRAGMA enable_verification;

Disable query verification:

PRAGMA disable_verification;

Enable force parallel query processing:

PRAGMA verify_parallelism;

Disable force parallel query processing:

PRAGMA disable_verify_parallelism;
About this page

Last modified: 2024-07-16