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Connection pool

Each Client owns a hidden, per-coroutine connection pool. You never create or manage it directly. query, insert and insertBatch acquire a physical connection when they start and release it when they finish (a streamed query() result holds its connection until it is fully read).

Why per-coroutine

Concurrent coroutines must not share one socket; their reads and writes would interleave on the wire. So each coroutine that runs a query gets its own connection from the pool, and several queries can be in flight at once:

use function Async\spawn;
use function Async\await_all;

$client = new Client(['host' => '127.0.0.1']);

// These three run concurrently, each on its own pooled connection.
[$results] = await_all([
    spawn(fn() => $client->query("SELECT sleep(1), 1 AS n")->fetchAll()),
    spawn(fn() => $client->query("SELECT sleep(1), 2 AS n")->fetchAll()),
    spawn(fn() => $client->query("SELECT sleep(1), 3 AS n")->fetchAll()),
]);

Sizing

'pool' => ['max' => N] (default 10) caps the number of physical connections. When all max are busy, a further acquirer waits until one is released. Connections are created lazily, on demand.

Failure handling

A connection that dies mid-operation (peer reset, timeout, protocol error) is marked broken and destroyed instead of being returned to the pool. The next acquire transparently gets a fresh, healthy connection, so a single dropped connection does not surface twice.

getPool(): \Async\Pool

For advanced needs, getPool() returns the underlying TrueAsync Async\Pool wrapper:

$pool = $client->getPool();

$pool->count();        // total connections
$pool->idleCount();    // idle (available)
$pool->activeCount();  // in use

$pool->getState();     // circuit-breaker state
$pool->close();        // close the pool

This is an escape hatch; for normal use you never touch it. The exact surface is the standard TrueAsync pool wrapper (stats, circuit breaker, lifecycle, manual acquire/tryAcquire/release).

The wrapper is valid only while the owning Client is alive: destroying the Client closes the pool, so a wrapper kept past that point refers to a closed pool.