This engine provides integration with [Amazon S3](https://aws.amazon.com/s3/) ecosystem and allows streaming import. This engine is similar to the [Kafka](../../../engines/table-engines/integrations/kafka.md), [RabbitMQ](../../../engines/table-engines/integrations/rabbitmq.md) engines, but provides S3-specific features.
## Create Table {#creating-a-table}
``` sql
CREATE TABLE s3_queue_engine_table (name String, value UInt32)
`S3Queue` parameters are the same as `S3` table engine supports. See parameters section [here](../../../engines/table-engines/integrations/s3.md#parameters).
- 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.
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.
Determines the additional wait time added to the previous polling interval when no new files are found. The next poll occurs after the sum of the previous interval and this backoff value, or the maximum interval, whichever is lower.
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.
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.
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.
`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`.
`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](../../../sql-reference/statements/create/view.md). To do this:
1. Use the engine to create a table for consuming from specified path in S3 and consider it a data stream.
2. Create a table with the desired structure.
3. 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:
``` sql
CREATE TABLE s3queue_engine_table (name String, value UInt32)
For more information about virtual columns see [here](../../../engines/table-engines/index.md#table_engines-virtual_columns).
## Wildcards In Path {#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](../../../sql-reference/table-functions/remote.md) table function.
-`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;
2.`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.
1.`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.
