Random choice

The YDB SDK uses the random_choice (uniform random) balancing algorithm by default, except the C++ SDK, which defaults to "prefer the nearest data center".

Below are examples of explicitly setting the "random choice" balancing algorithm in different YDB SDKs.

C++

Python

Native SDK

database/sql

package main

import (
  "context"
  "os"

  "github.com/ydb-platform/ydb-go-sdk/v3"
  "github.com/ydb-platform/ydb-go-sdk/v3/balancers"
)

func main() {
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel()
  db, err := ydb.Open(ctx,
    os.Getenv("YDB_CONNECTION_STRING"),
    ydb.WithBalancer(
      balancers.RandomChoice(),
    ),
  )
  if err != nil {
    panic(err)
  }
  defer db.Close(ctx)
  // ...
}

Client-side balancing in the YDB database/sql driver happens only when opening a new connection (in database/sql terms), which maps to a YDB session on a specific node. After the session is created, all queries on that session go to that node. Queries on the same YDB session are not balanced across nodes.

Example for "random choice" balancing:

package main

import (
  "context"
  "database/sql"
  "os"

  "github.com/ydb-platform/ydb-go-sdk/v3"
  "github.com/ydb-platform/ydb-go-sdk/v3/balancers"
)

func main() {
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel()
  nativeDriver, err := ydb.Open(ctx,
    os.Getenv("YDB_CONNECTION_STRING"),
    ydb.WithBalancer(
      balancers.RandomChoice(),
    ),
  )
  if err != nil {
    panic(err)
  }
  defer nativeDriver.Close(ctx)

  connector, err := ydb.Connector(nativeDriver)
  if err != nil {
    panic(err)
  }

  db := sql.OpenDB(connector)
  defer db.Close()
  // ...
}

#include <ydb-cpp-sdk/client/driver/driver.h>

int main() {
  auto connectionString = std::string(std::getenv("YDB_CONNECTION_STRING"));

  auto driverConfig = NYdb::TDriverConfig(connectionString)
    .SetBalancingPolicy(NYdb::TBalancingPolicy::UseAllNodes());

  NYdb::TDriver driver(driverConfig);
  // ...
  driver.Stop(true);
  return 0;
}

Native SDK

Native SDK (Asyncio)

SQLAlchemy

import os
import ydb

driver_config = ydb.DriverConfig(
    endpoint=os.environ["YDB_ENDPOINT"],
    database=os.environ["YDB_DATABASE"],
    credentials=ydb.credentials_from_env_variables(),
    use_all_nodes=True,  # uniform random choice
)

with ydb.Driver(driver_config) as driver:
    driver.wait(timeout=5)
    # ...

import os
import ydb
import asyncio

async def ydb_init():
    driver_config = ydb.DriverConfig(
        endpoint=os.environ["YDB_ENDPOINT"],
        database=os.environ["YDB_DATABASE"],
        credentials=ydb.credentials_from_env_variables(),
        use_all_nodes=True,  # uniform random choice
    )
    async with ydb.aio.Driver(driver_config) as driver:
        await driver.wait()
        # ...

asyncio.run(ydb_init())

import os
import sqlalchemy as sa

engine = sa.create_engine(
    os.environ["YDB_SQLALCHEMY_URL"],
    connect_args={
        "driver_config_kwargs": {
            "use_all_nodes": True,  # uniform random choice
        }
    },
)

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Overview

Prefer the nearest data center