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87 lines
4.0 KiB
Markdown
87 lines
4.0 KiB
Markdown
# StripeLog
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This engine belongs to the family of log engines. See the common properties of log engines and their differences in the [Log Engine Family](log_family.md) article.
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Use this engine in scenarios when you need to write many tables with a small amount of data (less than 1 million rows).
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## Creating a Table {#table_engines-stripelog-creating-a-table}
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```sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
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(
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column1_name [type1] [DEFAULT|MATERIALIZED|ALIAS expr1],
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column2_name [type2] [DEFAULT|MATERIALIZED|ALIAS expr2],
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...
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) ENGINE = StripeLog
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```
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See the detailed description of the [CREATE TABLE](../../query_language/create.md#create-table-query) query.
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## Writing the Data {#table_engines-stripelog-writing-the-data}
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The `StripeLog` engine stores all the columns in one file. For each `INSERT` query, ClickHouse appends the data block to the end of a table file, writing columns one by one.
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For each table ClickHouse writes the files:
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- `data.bin` — Data file.
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- `index.mrk` — File with marks. Marks contain offsets for each column of each data block inserted.
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The `StripeLog` engine does not support the `ALTER UPDATE` and `ALTER DELETE` operations.
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## Reading the Data {#table_engines-stripelog-reading-the-data}
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The file with marks allows ClickHouse to parallelize the reading of data. This means that a `SELECT` query returns rows in an unpredictable order. Use the `ORDER BY` clause to sort rows.
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## Example of Use {#table_engines-stripelog-example-of-use}
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Creating a table:
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```sql
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CREATE TABLE stripe_log_table
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(
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timestamp DateTime,
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message_type String,
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message String
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)
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ENGINE = StripeLog
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```
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Inserting data:
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```sql
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INSERT INTO stripe_log_table VALUES (now(),'REGULAR','The first regular message')
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INSERT INTO stripe_log_table VALUES (now(),'REGULAR','The second regular message'),(now(),'WARNING','The first warning message')
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```
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We used two `INSERT` queries to create two data blocks inside the `data.bin` file.
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ClickHouse uses multiple threads when selecting data. Each thread reads a separate data block and returns resulting rows independently as it finishes. As a result, the order of blocks of rows in the output does not match the order of the same blocks in the input in most cases. For example:
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```sql
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SELECT * FROM stripe_log_table
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```
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```text
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┌───────────timestamp─┬─message_type─┬─message────────────────────┐
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│ 2019-01-18 14:27:32 │ REGULAR │ The second regular message │
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│ 2019-01-18 14:34:53 │ WARNING │ The first warning message │
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└─────────────────────┴──────────────┴────────────────────────────┘
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┌───────────timestamp─┬─message_type─┬─message───────────────────┐
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│ 2019-01-18 14:23:43 │ REGULAR │ The first regular message │
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└─────────────────────┴──────────────┴───────────────────────────┘
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```
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Sorting the results (ascending order by default):
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```sql
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SELECT * FROM stripe_log_table ORDER BY timestamp
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```
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```text
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┌───────────timestamp─┬─message_type─┬─message────────────────────┐
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│ 2019-01-18 14:23:43 │ REGULAR │ The first regular message │
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│ 2019-01-18 14:27:32 │ REGULAR │ The second regular message │
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│ 2019-01-18 14:34:53 │ WARNING │ The first warning message │
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└─────────────────────┴──────────────┴────────────────────────────┘
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```
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[Original article](https://clickhouse.tech/docs/en/operations/table_engines/stripelog/) <!--hide-->
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