@Rocky i am revisiting the PK on one of my tables and I see that it is limited to 32 bytes, is there a way that I can tell the size of a few fields in a table before I actually implement

Hey there! I'm Rocky. Re-evaluating your Primary Key (PK) strategy is a great idea, especially for performance and memory optimization. First, a quick correction: In StarRocks, the default maximum length of an encoded primary key value is actually 128 bytes, not 32. This limit is controlled by the

primary_key_limit_size

parameter in your

be.conf

(BE configuration). If you really need more, you can increase this value, though it will consume more memory and I/O. To check the size of your fields before implementing them as a PK, you can use the following methods: 1. For String Fields (VARCHAR, CHAR) StarRocks provides the

length()

function, which specifically returns the length of a string in bytes (unlike

char_length()

, which returns the number of characters). You can run a query like this to see the maximum byte size currently used in your data:

sql
SELECT 
    MAX(length(your_column_name)) as max_bytes,
    AVG(length(your_column_name)) as avg_bytes
FROM your_table;

2. For Fixed-Width Types If you are using numeric or date types, they have fixed byte sizes regardless of the value: * TINYINT: 1 byte * SMALLINT: 2 bytes * INT: 4 bytes * BIGINT: 8 bytes * LARGEINT: 16 bytes * DECIMAL: 16 bytes * DATE: 3 bytes * DATETIME: 8 bytes * BOOLEAN: 1 byte 3. Calculating Composite Primary Keys If your PK consists of multiple columns, the total size is the sum of the byte sizes of each column. For example, if you have a PK consisting of an

INT

(4 bytes) and a

VARCHAR

that contains strings up to 20 bytes long, your total PK size would be 24 bytes. Why does this matter? The primary key index is stored in memory (unless you enable the Persistent Index). Smaller primary keys lead to: * Lower memory consumption: Smaller keys mean more keys can fit in the same amount of RAM. * Faster performance: Smaller keys are faster to compare and search during upsert/delete operations. Pro-tip: If you find that your strings are too long but you still need them for uniqueness, consider if you can represent that data using a

BIGINT

or a shorter ID instead. Let me know if you have more questions about your table design! References • sql-reference/sql-functions/string-functions/character_length.md • sql-reference/sql-functions/string-functions/char_length.md • faq/Others.md • knowledge/usage/best-practice.md • sql-reference/sql-functions/string-functions/length.md • sql-reference/data-types/string-type/VARCHAR.md • sql-reference/data-types/string-type/CHAR.md

@Rocky how can i check that

primary_key_limit_size

param?

To check the value of the

primary_key_limit_size

parameter (and other Backend configurations), you have a few options: 1. Using SQL (Recommended) You can query the

information_schema.be_configs

table directly from your MySQL client. This is the easiest way to see the current effective value across all your BE nodes:

sql
SELECT * FROM information_schema.be_configs WHERE NAME = 'primary_key_limit_size';

2. Using the HTTP API Each Backend (BE) node provides a

/varz

endpoint that lists all configuration parameters. You can use

curl

to check it:

bash
curl http://<BE_IP>:<BE_HTTP_PORT>/varz | grep primary_key_limit_size

_Note: The default

<BE_HTTP_PORT>

is usually

8040

._ 3. Checking the Configuration File You can also check the configuration file on the server where the BE is running: * Path:

starrocks/be/conf/be.conf

* Open the file and look for

primary_key_limit_size

. If it's not listed, it is using the default value of 128 bytes. ────────── Important Notes on the Limit: * Default: 128 bytes. * What it limits: This is the maximum size of the encoded primary key. If you have a composite PK, the limit applies to the total sum of the key columns' byte sizes. * Mutable: This parameter is dynamic. You can change it without restarting the BE by using the

curl

command (though it's safer to update

be.conf

as well to make it persistent):

bash
    curl -X POST http://<BE_IP>:<BE_HTTP_PORT>/api/update_config?primary_key_limit_size=256

Warning: Increasing this will increase memory usage for the Primary Key index. References • administration/management/BE_configuration.md • sql-reference/information_schema/be_configs.md • best_practices/primarykey_table.md References • administration/management/BE_configuration.md • administration/management/FE_configuration.md • sql-reference/sql-statements/cluster-management/config_vars/ADMIN_SHOW_CONFIG.md • sql-reference/sql-statements/cluster-management/nodes_processes/SHOW_BACKENDS.md