feat: add POLLING_LIMIT_PER_HOST to limit concurrent requests per host

Each batch of feeds sent to the worker pool is now guaranteed to contain unique feed URLs.

When `POLLING_LIMIT_PER_HOST` is set, an additional limit is applied to the number of concurrent requests per hostname, helping to prevent overloading a single server.

Note: Additional requests may still be made during feed refresh. For example, to fetch feed icons or when the web scraper is enabled for a particular feed.

internal/api/category.go

@@ -143,6 +143,7 @@ func (h *handler) refreshCategory(w http.ResponseWriter, r *http.Request) {
 	batchBuilder.WithUserID(userID)
 	batchBuilder.WithCategoryID(categoryID)
 	batchBuilder.WithNextCheckExpired()
+	batchBuilder.WithLimitPerHost(config.Opts.PollingLimitPerHost())
 
 	jobs, err := batchBuilder.FetchJobs()
 	if err != nil {

internal/api/feed.go

@@ -76,6 +76,7 @@ func (h *handler) refreshAllFeeds(w http.ResponseWriter, r *http.Request) {
 	batchBuilder.WithoutDisabledFeeds()
 	batchBuilder.WithNextCheckExpired()
 	batchBuilder.WithUserID(userID)
+	batchBuilder.WithLimitPerHost(config.Opts.PollingLimitPerHost())
 
 	jobs, err := batchBuilder.FetchJobs()
 	if err != nil {

internal/cli/refresh_feeds.go

@@ -25,6 +25,7 @@ func refreshFeeds(store *storage.Storage) {
 	batchBuilder.WithErrorLimit(config.Opts.PollingParsingErrorLimit())
 	batchBuilder.WithoutDisabledFeeds()
 	batchBuilder.WithNextCheckExpired()
+	batchBuilder.WithLimitPerHost(config.Opts.PollingLimitPerHost())
 
 	jobs, err := batchBuilder.FetchJobs()
 	if err != nil {
@@ -39,6 +40,8 @@ func refreshFeeds(store *storage.Storage) {
 		slog.Int("batch_size", config.Opts.BatchSize()),
 	)
 
+	slog.Debug("Feed URLs in this batch", slog.Any("feed_urls", jobs.FeedURLs()))
+
 	var jobQueue = make(chan model.Job, nbJobs)
 
 	slog.Info("Starting a pool of workers",

internal/cli/scheduler.go

@@ -21,6 +21,7 @@ func runScheduler(store *storage.Storage, pool *worker.Pool) {
 		config.Opts.PollingFrequency(),
 		config.Opts.BatchSize(),
 		config.Opts.PollingParsingErrorLimit(),
+		config.Opts.PollingLimitPerHost(),
 	)
 
 	go cleanupScheduler(
@@ -29,7 +30,7 @@ func runScheduler(store *storage.Storage, pool *worker.Pool) {
 	)
 }
 
-func feedScheduler(store *storage.Storage, pool *worker.Pool, frequency, batchSize, errorLimit int) {
+func feedScheduler(store *storage.Storage, pool *worker.Pool, frequency, batchSize, errorLimit, limitPerHost int) {
 	for range time.Tick(time.Duration(frequency) * time.Minute) {
 		// Generate a batch of feeds for any user that has feeds to refresh.
 		batchBuilder := store.NewBatchBuilder()
@@ -37,6 +38,7 @@ func feedScheduler(store *storage.Storage, pool *worker.Pool, frequency, batchSi
 		batchBuilder.WithErrorLimit(errorLimit)
 		batchBuilder.WithoutDisabledFeeds()
 		batchBuilder.WithNextCheckExpired()
+		batchBuilder.WithLimitPerHost(limitPerHost)
 
 		if jobs, err := batchBuilder.FetchJobs(); err != nil {
 			slog.Error("Unable to fetch jobs from database", slog.Any("error", err))
@@ -44,6 +46,7 @@ func feedScheduler(store *storage.Storage, pool *worker.Pool, frequency, batchSi
 			slog.Info("Created a batch of feeds",
 				slog.Int("nb_jobs", len(jobs)),
 			)
+			slog.Debug("Feed URLs in this batch", slog.Any("feed_urls", jobs.FeedURLs()))
 			pool.Push(jobs)
 		}
 	}

internal/config/config_test.go

@@ -2104,3 +2104,36 @@ func TestInvalidHTTPClientProxy(t *testing.T) {
 		t.Fatalf(`Expected error for invalid HTTP_CLIENT_PROXY value, but got none`)
 	}
 }
+
+func TestDefaultPollingLimitPerHost(t *testing.T) {
+	os.Clearenv()
+
+	parser := NewParser()
+	opts, err := parser.ParseEnvironmentVariables()
+	if err != nil {
+		t.Fatalf(`Parsing failure: %v`, err)
+	}
+
+	expected := 0
+	result := opts.PollingLimitPerHost()
+	if result != expected {
+		t.Fatalf(`Unexpected default PollingLimitPerHost value, got %v instead of %v`, result, expected)
+	}
+}
+
+func TestCustomPollingLimitPerHost(t *testing.T) {
+	os.Clearenv()
+	os.Setenv("POLLING_LIMIT_PER_HOST", "10")
+
+	parser := NewParser()
+	opts, err := parser.ParseEnvironmentVariables()
+	if err != nil {
+		t.Fatalf(`Parsing failure: %v`, err)
+	}
+
+	expected := 10
+	result := opts.PollingLimitPerHost()
+	if result != expected {
+		t.Fatalf(`Unexpected custom PollingLimitPerHost value, got %v instead of %v`, result, expected)
+	}
+}

internal/config/options.go

@@ -130,16 +130,17 @@ type options struct {
 	cleanupArchiveUnreadDays           int
 	cleanupArchiveBatchSize            int
 	cleanupRemoveSessionsDays          int
-	pollingFrequency                   int
 	forceRefreshInterval               int
 	batchSize                          int
-	pollingScheduler                   string
 	schedulerEntryFrequencyMinInterval int
 	schedulerEntryFrequencyMaxInterval int
 	schedulerEntryFrequencyFactor      int
 	schedulerRoundRobinMinInterval     int
 	schedulerRoundRobinMaxInterval     int
+	pollingFrequency                   int
+	pollingLimitPerHost                int
 	pollingParsingErrorLimit           int
+	pollingScheduler                   string
 	workerPoolSize                     int
 	createAdmin                        bool
 	adminUsername                      string
@@ -390,11 +391,6 @@ func (o *options) WorkerPoolSize() int {
 	return o.workerPoolSize
 }
 
-// PollingFrequency returns the interval to refresh feeds in the background.
-func (o *options) PollingFrequency() int {
-	return o.pollingFrequency
-}
-
 // ForceRefreshInterval returns the force refresh interval
 func (o *options) ForceRefreshInterval() int {
 	return o.forceRefreshInterval
@@ -405,6 +401,22 @@ func (o *options) BatchSize() int {
 	return o.batchSize
 }
 
+// PollingFrequency returns the interval to refresh feeds in the background.
+func (o *options) PollingFrequency() int {
+	return o.pollingFrequency
+}
+
+// PollingLimitPerHost returns the limit of concurrent requests per host.
+// Set to zero to disable.
+func (o *options) PollingLimitPerHost() int {
+	return o.pollingLimitPerHost
+}
+
+// PollingParsingErrorLimit returns the limit of errors when to stop polling.
+func (o *options) PollingParsingErrorLimit() int {
+	return o.pollingParsingErrorLimit
+}
+
 // PollingScheduler returns the scheduler used for polling feeds.
 func (o *options) PollingScheduler() string {
 	return o.pollingScheduler
@@ -433,11 +445,6 @@ func (o *options) SchedulerRoundRobinMaxInterval() int {
 	return o.schedulerRoundRobinMaxInterval
 }
 
-// PollingParsingErrorLimit returns the limit of errors when to stop polling.
-func (o *options) PollingParsingErrorLimit() int {
-	return o.pollingParsingErrorLimit
-}
-
 // IsOAuth2UserCreationAllowed returns true if user creation is allowed for OAuth2 users.
 func (o *options) IsOAuth2UserCreationAllowed() bool {
 	return o.oauth2UserCreationAllowed
@@ -762,8 +769,9 @@ func (o *options) SortedOptions(redactSecret bool) []*option {
 		"OAUTH2_REDIRECT_URL":                    o.oauth2RedirectURL,
 		"OAUTH2_USER_CREATION":                   o.oauth2UserCreationAllowed,
 		"DISABLE_LOCAL_AUTH":                     o.disableLocalAuth,
-		"POLLING_FREQUENCY":                      o.pollingFrequency,
 		"FORCE_REFRESH_INTERVAL":                 o.forceRefreshInterval,
+		"POLLING_FREQUENCY":                      o.pollingFrequency,
+		"POLLING_LIMIT_PER_HOST":                 o.pollingLimitPerHost,
 		"POLLING_PARSING_ERROR_LIMIT":            o.pollingParsingErrorLimit,
 		"POLLING_SCHEDULER":                      o.pollingScheduler,
 		"MEDIA_PROXY_HTTP_CLIENT_TIMEOUT":        o.mediaProxyHTTPClientTimeout,

internal/config/parser.go

@@ -137,12 +137,16 @@ func (p *parser) parseLines(lines []string) (err error) {
 			p.opts.cleanupRemoveSessionsDays = parseInt(value, defaultCleanupRemoveSessionsDays)
 		case "WORKER_POOL_SIZE":
 			p.opts.workerPoolSize = parseInt(value, defaultWorkerPoolSize)
-		case "POLLING_FREQUENCY":
-			p.opts.pollingFrequency = parseInt(value, defaultPollingFrequency)
 		case "FORCE_REFRESH_INTERVAL":
 			p.opts.forceRefreshInterval = parseInt(value, defaultForceRefreshInterval)
 		case "BATCH_SIZE":
 			p.opts.batchSize = parseInt(value, defaultBatchSize)
+		case "POLLING_FREQUENCY":
+			p.opts.pollingFrequency = parseInt(value, defaultPollingFrequency)
+		case "POLLING_LIMIT_PER_HOST":
+			p.opts.pollingLimitPerHost = parseInt(value, 0)
+		case "POLLING_PARSING_ERROR_LIMIT":
+			p.opts.pollingParsingErrorLimit = parseInt(value, defaultPollingParsingErrorLimit)
 		case "POLLING_SCHEDULER":
 			p.opts.pollingScheduler = strings.ToLower(parseString(value, defaultPollingScheduler))
 		case "SCHEDULER_ENTRY_FREQUENCY_MAX_INTERVAL":
@@ -155,8 +159,6 @@ func (p *parser) parseLines(lines []string) (err error) {
 			p.opts.schedulerRoundRobinMinInterval = parseInt(value, defaultSchedulerRoundRobinMinInterval)
 		case "SCHEDULER_ROUND_ROBIN_MAX_INTERVAL":
 			p.opts.schedulerRoundRobinMaxInterval = parseInt(value, defaultSchedulerRoundRobinMaxInterval)
-		case "POLLING_PARSING_ERROR_LIMIT":
-			p.opts.pollingParsingErrorLimit = parseInt(value, defaultPollingParsingErrorLimit)
 		case "MEDIA_PROXY_HTTP_CLIENT_TIMEOUT":
 			p.opts.mediaProxyHTTPClientTimeout = parseInt(value, defaultMediaProxyHTTPClientTimeout)
 		case "MEDIA_PROXY_MODE":

internal/model/job.go

@@ -7,7 +7,18 @@ package model // import "miniflux.app/v2/internal/model"
 type Job struct {
 	UserID  int64
 	FeedID  int64
+	FeedURL string
 }
 
 // JobList represents a list of jobs.
 type JobList []Job
+
+// FeedURLs returns a list of feed URLs from the job list.
+// This is useful for logging or debugging purposes to see which feeds are being processed.
+func (jl *JobList) FeedURLs() []string {
+	feedURLs := make([]string, len(*jl))
+	for i, job := range *jl {
+		feedURLs[i] = job.FeedURL
+	}
+	return feedURLs
+}

internal/storage/batch.go

@@ -6,9 +6,11 @@ package storage // import "miniflux.app/v2/internal/storage"
 import (
 	"database/sql"
 	"fmt"
+	"log/slog"
 	"strings"
 
 	"miniflux.app/v2/internal/model"
+	"miniflux.app/v2/internal/urllib"
 )
 
 type BatchBuilder struct {
@@ -16,6 +18,7 @@ type BatchBuilder struct {
 	args         []any
 	conditions   []string
 	limit        int
+	limitPerHost int
 }
 
 func (s *Storage) NewBatchBuilder() *BatchBuilder {
@@ -59,15 +62,27 @@ func (b *BatchBuilder) WithoutDisabledFeeds() *BatchBuilder {
 	return b
 }
 
+func (b *BatchBuilder) WithLimitPerHost(limit int) *BatchBuilder {
+	if limit > 0 {
+		b.limitPerHost = limit
+	}
+	return b
+}
+
+// FetchJobs retrieves a batch of jobs based on the conditions set in the builder.
+// It ensures that each job is unique by feed URL to avoid making too many concurrent requests to the same website.
+// When limitPerHost is set, it limits the number of jobs per feed hostname to prevent overwhelming a single host.
 func (b *BatchBuilder) FetchJobs() (model.JobList, error) {
-	query := `SELECT id, user_id FROM feeds`
+	query := `SELECT DISTINCT ON (feed_url) id, user_id, feed_url FROM feeds`
 
 	if len(b.conditions) > 0 {
 		query += " WHERE " + strings.Join(b.conditions, " AND ")
 	}
 
+	query += " ORDER BY feed_url, next_check_at ASC"
+
 	if b.limit > 0 {
-		query += fmt.Sprintf(" ORDER BY next_check_at ASC LIMIT %d", b.limit)
+		query += fmt.Sprintf(" LIMIT %d", b.limit)
 	}
 
 	rows, err := b.db.Query(query, b.args...)
@@ -77,15 +92,34 @@ func (b *BatchBuilder) FetchJobs() (model.JobList, error) {
 	defer rows.Close()
 
 	jobs := make(model.JobList, 0, b.limit)
+	hosts := make(map[string]int)
 
 	for rows.Next() {
 		var job model.Job
-		if err := rows.Scan(&job.FeedID, &job.UserID); err != nil {
-			return nil, fmt.Errorf(`store: unable to fetch job: %v`, err)
+		if err := rows.Scan(&job.FeedID, &job.UserID, &job.FeedURL); err != nil {
+			return nil, fmt.Errorf(`store: unable to fetch job record: %v`, err)
+		}
+
+		if b.limitPerHost > 0 {
+			feedHostname := urllib.Domain(job.FeedURL)
+			if hosts[feedHostname] >= b.limitPerHost {
+				slog.Debug("Feed host limit reached for this batch",
+					slog.String("feed_url", job.FeedURL),
+					slog.String("feed_hostname", feedHostname),
+					slog.Int("limit_per_host", b.limitPerHost),
+					slog.Int("current", hosts[feedHostname]),
+				)
+				continue
+			}
+			hosts[feedHostname]++
 		}
 
 		jobs = append(jobs, job)
 	}
 
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf(`store: error iterating on job records: %v`, err)
+	}
+
 	return jobs, nil
 }

internal/ui/category_refresh.go

@@ -43,6 +43,7 @@ func (h *handler) refreshCategory(w http.ResponseWriter, r *http.Request) int64
 		batchBuilder.WithoutDisabledFeeds()
 		batchBuilder.WithUserID(userID)
 		batchBuilder.WithCategoryID(categoryID)
+		batchBuilder.WithLimitPerHost(config.Opts.PollingLimitPerHost())
 
 		jobs, err := batchBuilder.FetchJobs()
 		if err != nil {

internal/ui/feed_refresh.go

@@ -47,6 +47,7 @@ func (h *handler) refreshAllFeeds(w http.ResponseWriter, r *http.Request) {
 		batchBuilder := h.store.NewBatchBuilder()
 		batchBuilder.WithoutDisabledFeeds()
 		batchBuilder.WithUserID(userID)
+		batchBuilder.WithLimitPerHost(config.Opts.PollingLimitPerHost())
 
 		jobs, err := batchBuilder.FetchJobs()
 		if err != nil {

internal/worker/worker.go

@@ -32,6 +32,7 @@ func (w *worker) Run(c <-chan model.Job) {
 			slog.Int("worker_id", w.id),
 			slog.Int64("user_id", job.UserID),
 			slog.Int64("feed_id", job.FeedID),
+			slog.String("feed_url", job.FeedURL),
 		)
 
 		startTime := time.Now()

miniflux.1

@@ -1,5 +1,5 @@
 .\" Manpage for miniflux.
-.TH "MINIFLUX" "1" "June 23, 2025" "\ \&" "\ \&"
+.TH "MINIFLUX" "1" "August 8, 2025" "\ \&" "\ \&"
 
 .SH NAME
 miniflux \- Minimalist and opinionated feed reader
@@ -490,19 +490,32 @@ Refresh interval in minutes for feeds\&.
 .br
 Default is 60 minutes\&.
 .TP
+.B POLLING_LIMIT_PER_HOST
+Limits the number of concurrent requests to the same hostname when polling feeds.
+.br
+This helps prevent overwhelming a single server during batch processing by the worker pool.
+.br
+Default is 0 (disabled)\&.
+.TP
 .B POLLING_PARSING_ERROR_LIMIT
-The maximum number of parsing errors that the program will try before stopping polling a feed. Once the limit is reached, the user must refresh the feed manually. Set to 0 for unlimited.
+The maximum number of parsing errors that the program will try before stopping polling a feed.
+.br
+Once the limit is reached, the user must refresh the feed manually. Set to 0 for unlimited.
 .br
 Default is 3\&.
 .TP
 .B POLLING_SCHEDULER
-Scheduler used for polling feeds. Possible values are "round_robin" or "entry_frequency"\&.
+Determines the strategy used to schedule feed polling.
 .br
-The maximum number of feeds polled for a given period is subject to POLLING_FREQUENCY and BATCH_SIZE\&.
+Supported values are "round_robin" and "entry_frequency".
 .br
-When "entry_frequency" is selected, the refresh interval for a given feed is equal to the average updating interval of the last week of the feed\&.
+- "round_robin": Feeds are polled in a fixed, rotating order.
 .br
-The actual number of feeds polled will not exceed the maximum number of feeds that could be polled for a given period\&.
+- "entry_frequency": The polling interval for each feed is based on the average update frequency over the past week.
+.br
+The number of feeds polled in a given period is limited by the POLLING_FREQUENCY and BATCH_SIZE settings.
+.br
+Regardless of the scheduler used, the total number of polled feeds will not exceed the maximum allowed per polling cycle.
 .br
 Default is "round_robin"\&.
 .TP