Settings

The qCrawl settings allows you to customize the behaviour of all the components. The settings can be populated through different mechanisms, which are described below.

For middleware-specific settings, refer to the respective middleware documentation.

Configuration precedence

qCrawl has the following precedence order for applying settings:

flowchart LR
    A(qCrawl defaults) --> B(TOML Config file) --> C(Environment variables) --> D(CLI) --> E(Programmatic overrides)

Best practices

qCrawl's defaults are not supposed to be changed for per-project needs. Instead, use the configuration layers as intended:

TOML Config file

Use a config file (e.g., config.toml) for project-wide reproducible settings.
Store non-sensitive settings like queue backend type, concurrency limits, timeouts.
Load config file via Settings.load(config_file="config.toml").

Example usage:

config.toml

# Use: runtime_settings = Settings.load(config_file="config.toml")

CONCURRENCY = 20
CONCURRENCY_PER_DOMAIN = 4
DELAY_PER_DOMAIN = 0.5
TIMEOUT = 45.0
MAX_RETRIES = 5
USER_AGENT = "MyCrawler/1.0"

QUEUE_BACKEND = "disk"  # or "memory", "redis"

[QUEUE_BACKENDS.disk]
class = "qcrawl.core.queues.disk.DiskQueue"
path = ""  # Empty/null = system temp dir (cross-platform)
maxsize = 0  # Max requests count (0 = unlimited)

Environment variables

Use environment variables for deployment/CI values and secrets.

Example usage:

export QCRAWL_CONCURRENCY="20"
export QCRAWL_CONCURRENCY_PER_DOMAIN="4"
export QCRAWL_DELAY_PER_DOMAIN="0.5"
export QCRAWL_TIMEOUT="45.0"
export QCRAWL_MAX_RETRIES="5"
export QCRAWL_USER_AGENT="MyCrawler/1.0"

# Queue backend selection
export QCRAWL_QUEUE_BACKEND="disk"  # or "memory", "redis"

# Disk queue configuration (optional)
export QCRAWL_QUEUE_BACKENDS__disk__path="/var/qcrawl/queue"
export QCRAWL_QUEUE_BACKENDS__disk__maxsize="10000"  # Max requests count

Warning

Never commit secrets into repository config files.

CLI

Use CLI arguments for CI test jobs or quick overrides for one-off runs.

Example usage:

qcrawl mypackage.spiders:QuotesSpider \
  -s CONCURRENCY=20 \
  -s CONCURRENCY_PER_DOMAIN=4 \
  -s DELAY_PER_DOMAIN=0.5 \
  -s TIMEOUT=45.0 \
  -s MAX_RETRIES=5 \
  -s USER_AGENT="MyCrawler/1.0" \
  -s QUEUE_BACKEND=disk \
  -s QUEUE_BACKENDS.disk.path=/tmp/my_queue \
  -s QUEUE_BACKENDS.disk.maxsize=10000

Warning

CLI args may appear in process lists exposing sensitive data.

Programmatic / per-spider

Use per-spider class attributes, constructor args, or custom_settings for fine-grained behavior.

Example usage:

from qcrawl.core.spider import Spider

class MySpider(Spider):
    name = "my_spider"
    start_urls = ["https://example.com"]

    custom_settings = {
        "CONCURRENCY": 20,
        "CONCURRENCY_PER_DOMAIN": 4,
        "DELAY_PER_DOMAIN": 0.5,
        "TIMEOUT": 45.0,
        "MAX_RETRIES": 5,
        "USER_AGENT": "MyCrawler/1.0",
        "QUEUE_BACKEND": "disk",
        "QUEUE_BACKENDS": {
            "disk": {
                "path": "/tmp/my_spider_queue",
                "maxsize": 10000,  # Max requests count
            }
        },
    }

    async def parse(self, response):
        ...

Settings reference

Queue settings

Setting	Type	Default	Env variable	Notes
`QUEUE_BACKEND`	`str`	`memory`	`QCRAWL_QUEUE_BACKEND`	Backend to use: `memory`, `disk`, `redis`, or custom
`QUEUE_BACKENDS`	`dict`	see below	`QCRAWL_QUEUE_BACKENDS`	Mapping of backend name → backend config (see structure below)

QUEUE_BACKENDS structure:

QUEUE_BACKEND = "memory"  # or "disk", "redis"

[QUEUE_BACKENDS.memory]
class = "qcrawl.core.queues.memory.MemoryPriorityQueue"
maxsize = 0  # Max requests count (0 = unlimited)

[QUEUE_BACKENDS.disk]
class = "qcrawl.core.queues.disk.DiskQueue"
path = ""  # Empty/null = system temp dir (cross-platform)
maxsize = 0  # Max requests count (0 = unlimited)

[QUEUE_BACKENDS.redis]
class = "qcrawl.core.queues.redis.RedisQueue"
# url = ""  # optional full connection URL (overrides host/port/user/password)
host = "localhost"
port = "6379"
user = "user"
password = "pass"
namespace = "qcrawl"
ssl = false
maxsize = 0  # Max requests count (0 = unlimited)
dedupe = false
update_priority = false
fingerprint_size = 16
item_ttl = 86400  # seconds, 0 = no expiration
dedupe_ttl = 604800  # seconds, 0 = no expiration
max_orphan_retries = 10
redis_kwargs = {}  # driver-specific options passed to redis client

Redis version compatibility

Redis server 7.4+ recommended for full TTL support (per-item expiration)

With Redis 7.4+: All features supported, including item_ttl and dedupe_ttl per-item expiration
With Redis 6.x: Basic queue operations work, but TTL features (item_ttl, dedupe_ttl) will fail with command errors (HEXPIRE not available)

Spider settings

Setting	Type	Default	Env variable	Validation
`CONCURRENCY`	`int`	`10`	`QCRAWL_CONCURRENCY`	must be 1-10000
`CONCURRENCY_PER_DOMAIN`	`int`	`2`	`QCRAWL_CONCURRENCY_PER_DOMAIN`	must be >= 1, cannot exceed CONCURRENCY
`DELAY_PER_DOMAIN`	`float`	`0.25`	`QCRAWL_DELAY_PER_DOMAIN`	must be >= 0
`MAX_DEPTH`	`int`	`0`	`QCRAWL_MAX_DEPTH`
`TIMEOUT`	`float`	`30.0`	`QCRAWL_TIMEOUT`	must be > 0
`MAX_RETRIES`	`int`	`3`	`QCRAWL_MAX_RETRIES`	must be >= 0
`USER_AGENT`	`str`	`'qCrawl/1.0'`	`QCRAWL_USER_AGENT`
`IGNORE_QUERY_PARAMS`	`set[str]`	`None`	`QCRAWL_IGNORE_QUERY_PARAMS`	mutually exclusive
`KEEP_QUERY_PARAMS`	`set[str]`	`None`	`QCRAWL_KEEP_QUERY_PARAMS`	mutually exclusive

Logging settings

Setting	Type	Default	Env variable	Validation
`LOG_LEVEL`	`str`	`'INFO'`	`QCRAWL_LOG_LEVEL`	`['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL']`
`LOG_FILE`	`str`	`None`	`QCRAWL_LOG_FILE`
`LOG_FORMAT`	`str`	`'%(asctime)s %(levelname)s %(name)s: %(message)s'`	`QCRAWL_LOG_FORMAT`
`LOG_DATEFORMAT`	`str`	`None`	`QCRAWL_LOG_DATEFORMAT`