/**
 * Connection management for GQLDB Node.js driver.
 */
import * as grpc from '@grpc/grpc-js';
import { GqldbConfig } from './config';
/** Manages a pool of connections to GQLDB servers */
export declare class ConnectionPool {
    private config;
    private connections;
    private closed;
    private healthCheckTimer?;
    constructor(config: GqldbConfig);
    private initConnections;
    private createConnection;
    /** Get a healthy connection from the pool */
    getConnection(): grpc.Client;
    /** Get a connection for a specific host */
    getConnectionForHost(host: string): grpc.Client;
    private startHealthCheck;
    /**
     * Health-check tick.  Connectivity-state semantics:
     *  - READY / IDLE         → healthy; reset the unhealthy counter.
     *  - CONNECTING           → transient; let the channel heal itself,
     *                            don't count toward unhealthy.
     *  - SHUTDOWN             → terminal; reconnect immediately.
     *  - TRANSIENT_FAILURE    → count toward unhealthy; reconnect only
     *                            after UNHEALTHY_RECONNECT_THRESHOLD
     *                            consecutive ticks.
     *
     * Reconnect replaces the pool's channel reference; it does NOT close
     * the old channel, so in-flight RPCs continue to completion on it.
     */
    private checkHealth;
    /**
     * Replace the pool's channel for `host` with a fresh one.
     *
     * Critically, does NOT close the old channel.  In-flight RPCs hold
     * their own reference to it via the client they were issued on and
     * continue to completion on that channel; the Node.js runtime's
     * garbage collector releases the old channel only after every
     * in-flight RPC has resolved.
     *
     * Earlier versions closed the old channel synchronously here, which
     * cancelled every pending RPC with a "Channel closed!"-style error.
     */
    /**
     * Rebuild every host's gRPC client in the pool.  Called by the client
     * on transport-level errors (UNAVAILABLE / connection reset) so the
     * next RPC gets a fresh channel.  Like reconnect, this does NOT close
     * old clients synchronously — in-flight RPCs hold them alive and gRPC
     * closes them naturally once those calls complete.
     */
    forceReconnectAll(): Promise<void>;
    private reconnect;
    /** Close all connections in the pool */
    close(): void;
    /** Get the number of healthy hosts */
    healthyHostCount(): number;
    /** Get the list of configured hosts */
    hosts(): string[];
    /** Check if the pool is closed */
    isClosed(): boolean;
}