S3Queue Table Engine

This engine provides integration with Amazon S3 ecosystem and allows streaming import. This engine is similar to the Kafka, RabbitMQ engines, but provides S3-specific features.

Create Table

CREATE TABLE s3_queue_engine_table (name String, value UInt32)
    ENGINE = S3Queue(path, [NOSIGN, | aws_access_key_id, aws_secret_access_key,] format, [compression])
    [SETTINGS]
    [mode = '',]
    [after_processing = 'keep',]
    [keeper_path = '',]
    [loading_retries = 0,]
    [processing_threads_num = 1,]
    [enable_logging_to_s3queue_log = 0,]
    [polling_min_timeout_ms = 1000,]
    [polling_max_timeout_ms = 10000,]
    [polling_backoff_ms = 0,]
    [tracked_file_ttl_sec = 0,]
    [tracked_files_limit = 1000,]
    [cleanup_interval_min_ms = 10000,]
    [cleanup_interval_max_ms = 30000,]

Danger

Before 24.7, it is required to use s3queue_ prefix for all settings apart from mode, after_processing and keeper_path.

Engine parameters

S3Queue parameters are the same as S3 table engine supports. See parameters section here.

Example

CREATE TABLE s3queue_engine_table (name String, value UInt32)
ENGINE=S3Queue('https://clickhouse-public-datasets.s3.amazonaws.com/my-test-bucket-768/*', 'CSV', 'gzip')
SETTINGS
    mode = 'unordered';

Using named collections:

<clickhouse>
    <named_collections>
        <s3queue_conf>
            <url>'https://clickhouse-public-datasets.s3.amazonaws.com/my-test-bucket-768/*</url>
            <access_key_id>test<access_key_id>
            <secret_access_key>test</secret_access_key>
        </s3queue_conf>
    </named_collections>
</clickhouse>

CREATE TABLE s3queue_engine_table (name String, value UInt32)
ENGINE=S3Queue(s3queue_conf, format = 'CSV', compression_method = 'gzip')
SETTINGS
    mode = 'ordered';

Settings

mode

Possible values:

unordered — With unordered mode, the set of all already processed files is tracked with persistent nodes in ZooKeeper.
ordered — With ordered mode, the files are processed in lexicographic order. It means that if file named 'BBB' was processed at some point and later on a file named 'AA' is added to the bucket, it will be ignored. Only the max name (in lexicographic sense) of the successfully consumed file, and the names of files that will be retried after unsuccessful loading attempt are being stored in ZooKeeper.

Default value: ordered in versions before 24.6. Starting with 24.6 there is no default value, the setting becomes required to be specified manually. For tables created on earlier versions the default value will remain Ordered for compatibility.

after_processing

Delete or keep file after successful processing. Possible values:

keep.
delete.

Default value: keep.

keeper_path

The path in ZooKeeper can be specified as a table engine setting or default path can be formed from the global configuration-provided path and table UUID. Possible values:

String.

Default value: /.

s3queue_loading_retries

Retry file loading up to specified number of times. By default, there are no retries. Possible values:

Positive integer.

Default value: 0.

s3queue_processing_threads_num

Number of threads to perform processing. Applies only for Unordered mode.

Default value: 1.

s3queue_enable_logging_to_s3queue_log

Enable logging to system.s3queue_log.

Default value: 0.

s3queue_polling_min_timeout_ms

Minimal timeout before next polling (in milliseconds).

Possible values:

Positive integer.

Default value: 1000.

s3queue_polling_max_timeout_ms

Maximum timeout before next polling (in milliseconds).

Possible values:

Positive integer.

Default value: 10000.

s3queue_polling_backoff_ms

Polling backoff (in milliseconds).

Possible values:

Positive integer.

Default value: 0.

s3queue_tracked_files_limit

Allows to limit the number of Zookeeper nodes if the 'unordered' mode is used, does nothing for 'ordered' mode. If limit reached the oldest processed files will be deleted from ZooKeeper node and processed again.

Possible values:

Positive integer.

Default value: 1000.

s3queue_tracked_file_ttl_sec

Maximum number of seconds to store processed files in ZooKeeper node (store forever by default) for 'unordered' mode, does nothing for 'ordered' mode. After the specified number of seconds, the file will be re-imported.

Possible values:

Positive integer.

Default value: 0.

s3queue_cleanup_interval_min_ms

For 'Ordered' mode. Defines a minimum boundary for reschedule interval for a background task, which is responsible for maintaining tracked file TTL and maximum tracked files set.

Default value: 10000.

s3queue_cleanup_interval_max_ms

For 'Ordered' mode. Defines a maximum boundary for reschedule interval for a background task, which is responsible for maintaining tracked file TTL and maximum tracked files set.

Default value: 30000.

s3queue_buckets

For 'Ordered' mode. Available since 24.6. If there are several replicas of S3Queue table, each working with the same metadata directory in keeper, the value of s3queue_buckets needs to be equal to at least the number of replicas. If s3queue_processing_threads setting is used as well, it makes sense to increase the value of s3queue_buckets setting even further, as it defines the actual parallelism of S3Queue processing.

S3-related Settings

Engine supports all s3 related settings. For more information about S3 settings see here.

S3Queue Ordered mode

S3Queue processing mode allows to store less metadata in ZooKeeper, but has a limitation that files, which added later by time, are required to have alphanumerically bigger names.

S3Queue ordered mode, as well as unordered, supports (s3queue_)processing_threads_num setting (s3queue_ prefix is optional), which allows to control number of threads, which would do processing of S3 files locally on the server. In addition, ordered mode also introduces another setting called (s3queue_)buckets which means "logical threads". It means that in distributed scenario, when there are several servers with S3Queue table replicas, where this setting defines the number of processing units. E.g. each processing thread on each S3Queue replica will try to lock a certain bucket for processing, each bucket is attributed to certain files by hash of the file name. Therefore, in distributed scenario it is highly recommended to have (s3queue_)buckets setting to be at least equal to the number of replicas or bigger. This is fine to have the number of buckets bigger than the number of replicas. The most optimal scenario would be for (s3queue_)buckets setting to equal a multiplication of number_of_replicas and (s3queue_)processing_threads_num. The setting (s3queue_)processing_threads_num is not recommended for usage before version 24.6. The setting (s3queue_)buckets is available starting with version 24.6.

Description

SELECT is not particularly useful for streaming import (except for debugging), because each file can be imported only once. It is more practical to create real-time threads using materialized views. To do this:

Use the engine to create a table for consuming from specified path in S3 and consider it a data stream.
Create a table with the desired structure.
Create a materialized view that converts data from the engine and puts it into a previously created table.

When the MATERIALIZED VIEW joins the engine, it starts collecting data in the background.

Example:

  CREATE TABLE s3queue_engine_table (name String, value UInt32)
    ENGINE=S3Queue('https://clickhouse-public-datasets.s3.amazonaws.com/my-test-bucket-768/*', 'CSV', 'gzip')
    SETTINGS
        mode = 'unordered';

  CREATE TABLE stats (name String, value UInt32)
    ENGINE = MergeTree() ORDER BY name;

  CREATE MATERIALIZED VIEW consumer TO stats
    AS SELECT name, value FROM s3queue_engine_table;

  SELECT * FROM stats ORDER BY name;

Virtual columns

_path — Path to the file.
_file — Name of the file.

For more information about virtual columns see here.

Wildcards In Path

path argument can specify multiple files using bash-like wildcards. For being processed file should exist and match to the whole path pattern. Listing of files is determined during SELECT (not at CREATE moment).

* — Substitutes any number of any characters except / including empty string.
** — Substitutes any number of any characters include / including empty string.
? — Substitutes any single character.
{some_string,another_string,yet_another_one} — Substitutes any of strings 'some_string', 'another_string', 'yet_another_one'.
{N..M} — Substitutes any number in range from N to M including both borders. N and M can have leading zeroes e.g. 000..078.

Constructions with {} are similar to the remote table function.

Limitations

Duplicated rows can be as a result of:

an exception happens during parsing in the middle of file processing and retries are enabled via s3queue_loading_retries;
S3Queue is configured on multiple servers pointing to the same path in zookeeper and keeper session expires before one server managed to commit processed file, which could lead to another server taking processing of the file, which could be partially or fully processed by the first server;
abnormal server termination.

S3Queue is configured on multiple servers pointing to the same path in zookeeper and Ordered mode is used, then s3queue_loading_retries will not work. This will be fixed soon.

Introspection

For introspection use system.s3queue stateless table and system.s3queue_log persistent table.

system.s3queue. This table is not persistent and shows in-memory state of S3Queue: which files are currently being processed, which files are processed or failed.

┌─statement──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE system.s3queue
(
    `database` String,
    `table` String,
    `file_name` String,
    `rows_processed` UInt64,
    `status` String,
    `processing_start_time` Nullable(DateTime),
    `processing_end_time` Nullable(DateTime),
    `ProfileEvents` Map(String, UInt64)
    `exception` String
)
ENGINE = SystemS3Queue
COMMENT 'Contains in-memory state of S3Queue metadata and currently processed rows per file.' │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

Example:

SELECT *
FROM system.s3queue

Row 1:
──────
zookeeper_path:        /clickhouse/s3queue/25ea5621-ae8c-40c7-96d0-cec959c5ab88/3b3f66a1-9866-4c2e-ba78-b6bfa154207e
file_name:             wikistat/original/pageviews-20150501-030000.gz
rows_processed:        5068534
status:                Processed
processing_start_time: 2023-10-13 13:09:48
processing_end_time:   2023-10-13 13:10:31
ProfileEvents:         {'ZooKeeperTransactions':3,'ZooKeeperGet':2,'ZooKeeperMulti':1,'SelectedRows':5068534,'SelectedBytes':198132283,'ContextLock':1,'S3QueueSetFileProcessingMicroseconds':2480,'S3QueueSetFileProcessedMicroseconds':9985,'S3QueuePullMicroseconds':273776,'LogTest':17}
exception:

system.s3queue_log. Persistent table. Has the same information as system.s3queue, but for processed and failed files.

The table has the following structure:

SHOW CREATE TABLE system.s3queue_log

Query id: 0ad619c3-0f2a-4ee4-8b40-c73d86e04314

┌─statement──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE system.s3queue_log
(
    `event_date` Date,
    `event_time` DateTime,
    `table_uuid` String,
    `file_name` String,
    `rows_processed` UInt64,
    `status` Enum8('Processed' = 0, 'Failed' = 1),
    `processing_start_time` Nullable(DateTime),
    `processing_end_time` Nullable(DateTime),
    `ProfileEvents` Map(String, UInt64),
    `exception` String
)
ENGINE = MergeTree
PARTITION BY toYYYYMM(event_date)
ORDER BY (event_date, event_time)
SETTINGS index_granularity = 8192 │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

In order to use system.s3queue_log define its configuration in server config file:

    <s3queue_log>
        <database>system</database>
        <table>s3queue_log</table>
    </s3queue_log>

Example:

SELECT *
FROM system.s3queue_log

Row 1:
──────
event_date:            2023-10-13
event_time:            2023-10-13 13:10:12
table_uuid:
file_name:             wikistat/original/pageviews-20150501-020000.gz
rows_processed:        5112621
status:                Processed
processing_start_time: 2023-10-13 13:09:48
processing_end_time:   2023-10-13 13:10:12
ProfileEvents:         {'ZooKeeperTransactions':3,'ZooKeeperGet':2,'ZooKeeperMulti':1,'SelectedRows':5112621,'SelectedBytes':198577687,'ContextLock':1,'S3QueueSetFileProcessingMicroseconds':1934,'S3QueueSetFileProcessedMicroseconds':17063,'S3QueuePullMicroseconds':5841972,'LogTest':17}
exception:

S3Queue Table Engine

Create Table​

Settings​

mode​

after_processing​

keeper_path​

s3queue_loading_retries​

s3queue_processing_threads_num​

s3queue_enable_logging_to_s3queue_log​

s3queue_polling_min_timeout_ms​

s3queue_polling_max_timeout_ms​

s3queue_polling_backoff_ms​

s3queue_tracked_files_limit​

s3queue_tracked_file_ttl_sec​

s3queue_cleanup_interval_min_ms​

s3queue_cleanup_interval_max_ms​

s3queue_buckets​

S3-related Settings​

S3Queue Ordered mode​

Description​

Virtual columns​

Wildcards In Path​

Limitations​

Introspection​

Create Table

Settings

mode

after_processing

keeper_path

s3queue_loading_retries

s3queue_processing_threads_num

s3queue_enable_logging_to_s3queue_log

s3queue_polling_min_timeout_ms

s3queue_polling_max_timeout_ms

s3queue_polling_backoff_ms

s3queue_tracked_files_limit

s3queue_tracked_file_ttl_sec

s3queue_cleanup_interval_min_ms

s3queue_cleanup_interval_max_ms

s3queue_buckets

S3-related Settings

S3Queue Ordered mode

Description

Virtual columns

Wildcards In Path

Limitations

Introspection