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[Bug]: Nextcloud keeps idle database connection for each preview generation enqueued for imaginary #65820

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[Bug]: Nextcloud keeps idle database connection for each preview generation enqueued for imaginary#65820
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0. Needs triagePending check for reproducibility or if it fits our roadmap34-feedbackbug

Description

@lukasfink1
lukasfink1
opened on Oct 23, 2026

⚠️ This issue respects the following points: ⚠️

  • This is not a troubleshooting question, general support matter, or webserver/proxy problem, but likely a bug (if unsure, ask the Community Help Forum).
  • This issue is not already reported on Github OR solved at the Community Help Forum (I've searched!).
  • I'm using a maintained major version of Nextcloud Server and tested against the latest patch level. (Supported major versions and current patch levels).
  • I agree to follow Nextcloud's Code of Conduct.
  • I've tried my best to provide clear reproduction steps that someone unfamiliar with this bug could use to reproduce it.

Bug description

When nextcloud has the generation of a lot of previews with imaginary enqueued, it keeps an idle connection to the database open for each enqueued image. As preview generation jobs can take some time, this can easily overwhelm the max_connections limit of postgresql.

The amount of open idle database connections is neither limited by the preview_concurrency_new nor preview_concurrency_all option.

I haven’t checked if the problem also applies to other preview generators.

Steps to reproduce

  1. Setup nextcloud to use postgres with a reasonable connection limit i. e. 100 and preview generation through imaginary.
  2. Run php occ preview:cleanup.
  3. Open a directory with a huge amount of images (≫100) and quickly scroll around in it.
  4. The log will be full of „Failed to connect to the database“ errors.

Even better is to use socat tcp-listen:9000,fork 'exec:sleep inf!!open:/dev/null' as a dummy imaginary that just takes forever to reply. In that case, the amount of open database connections can easily be perceived with netstat -n | grep 5432.

Expected behavior

There shouldn’t be an unbounded amount (the amount of enqueued image previews) of database connections open idling for an indefinite amount of time (the amount it takes to generate all enqueued image previews).

Either the connections should be bounded (e. g. to preview_concurrency_new) or they should be shortlived.

Nextcloud Server version

34

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.5

Web server

Apache (supported)

Database engine version

PostgreSQL

Is this bug present after an update or on a fresh install?

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

  • Default user-backend (database)
  • LDAP/ Active Directory
  • SSO - SAML
  • Other

Configuration report

{
    "system": {
        "htaccess.RewriteBase": "\/",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "password": "***REMOVED SENSITIVE VALUE***",
            "port": 0
        },
        "upgrade.disable-web": true,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "localhost"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "pgsql",
        "version": "34.0.5.1",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "maintenance": false,
        "preview_max_x": 2048,
        "preview_max_y": 2048,
        "jpeg_quality": 60,
        "preview_format": "webp",
        "enabledPreviewProviders": {
            "0": "OC\\Preview\\Imaginary",
            "1": "OC\\Preview\\Image",
            "2": "OC\\Preview\\MarkDown",
            "3": "OC\\Preview\\MP3",
            "4": "OC\\Preview\\TXT",
            "5": "OC\\Preview\\OpenDocument",
            "6": "OC\\Preview\\Movie",
            "7": "OC\\Preview\\Krita",
            "9": "OC\\Preview\\MKV",
            "10": "OC\\Preview\\AVI",
            "11": "OC\\Preview\\MP4",
            "13": "OC\\Preview\\ImaginaryPDF",
            "14": "OCA\\Eurooffice\\Preview"
        },
        "enable_previews": true,
        "trashbin_retention_obligation": "auto, 30",
        "versions_retention_obligation": "auto, 30",
        "activity_expire_days": 30,
        "maintenance_window_start": 100,
        "auth.bruteforce.protection.enabled": true,
        "ratelimit.protection.enabled": true,
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "preview_imaginary_url": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "serverid": 445,
        "app_install_overwrite": [],
        "data-fingerprint": "103b5af42cc2305eff756c8ce67a6c09"
    }
}

List of activated Apps

Enabled:
  - activity: 7.0.0
  - admin_audit: 1.24.0
  - appstore: 1.0.0
  - bruteforcesettings: 7.0.0
  - calendar: 6.6.3
  - circles: 34.0.0
  - cloud_federation_api: 1.18.0
  - comments: 1.24.0
  - contacts: 8.9.2
  - contactsinteraction: 1.15.0
  - cospend: 4.3.0
  - dashboard: 7.14.0
  - dav: 1.40.0
  - federatedfilesharing: 1.24.0
  - federation: 1.24.0
  - files: 2.6.0
  - files_downloadlimit: 5.2.0
  - files_external: 1.26.0
  - files_lock: 34.0.1
  - files_pdfviewer: 7.0.0
  - files_reminders: 1.7.0
  - files_sharing: 1.26.0
  - files_trashbin: 1.24.0
  - files_versions: 1.27.0
  - firstrunwizard: 7.0.0-dev.0
  - forms: 5.4.1
  - logreader: 7.0.0
  - lookup_server_connector: 1.22.0
  - nextcloud_announcements: 6.0.0
  - notifications: 7.0.0-dev.1
  - oauth2: 1.22.0
  - office: 1.0.0
  - password_policy: 6.0.0-dev.0
  - photos: 7.0.0
  - polls: 9.3.0
  - privacy: 6.0.0-dev.1
  - profile: 1.3.0
  - provisioning_api: 1.24.0
  - recommendations: 7.0.0
  - related_resources: 5.0.0-dev.0
  - serverinfo: 6.0.0
  - settings: 1.17.0
  - sharebymail: 1.24.0
  - support: 6.0.0
  - survey_client: 6.0.0-dev.0
  - suspicious_login: 12.0.0-dev.0
  - systemtags: 1.24.0
  - tasks: 0.18.1
  - text: 8.0.0
  - theming: 2.9.0
  - twofactor_backupcodes: 1.23.0
  - twofactor_nextcloud_notification: 8.0.0
  - twofactor_totp: 16.0.0
  - updatenotification: 1.24.0
  - user_status: 1.14.0
  - viewer: 7.0.0-dev.0
  - weather_status: 1.14.0
  - webhook_listeners: 1.6.0
  - workflowengine: 2.16.0
Disabled:
  - app_api: 34.0.0 (installed 5.0.2)
  - encryption: 2.22.0
  - spreed: 24.0.6 (installed 24.0.6)
  - user_ldap: 1.25.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

{"reqId":"4gm4v8xSHKHhUMLRggEU","level":3,"time":"2026-10-23T18:48:00+00:00","remoteAddr":"2001:7c7:2128:600:629a:22e6:b4e9:7ca1","user":"admin","app":"index","method":"GET","url":"/core/preview?fileId=215122&x=128&y=128&mimeFallback=true&v=343048&a=0","scriptName":"/index.php","message":"Failed to connect to the database: An exception occurred in the driver: SQLSTATE[08006] [7] connection to server on socket \"/run/postgresql/.s.PGSQL.5432\" failed: FATAL:  remaining connection slots are reserved for roles with the SUPERUSER attribute","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:158.0) Gecko/20100101 Firefox/158.0","version":"34.0.5.1","exception":{"Exception":"Doctrine\\DBAL\\Exception","Message":"Failed to connect to the database: An exception occurred in the driver: SQLSTATE[08006] [7] connection to server on socket \"/run/postgresql/.s.PGSQL.5432\" failed: FATAL:  remaining connection slots are reserved for roles with the SUPERUSER attribute","Code":7,"Trace":[{"file":"/var/www/html/3rdparty/doctrine/dbal/src/Connection.php","line":458,"function":"connect","class":"OC\\DB\\Connection","type":"->","args":[]},{"file":"/var/www/html/3rdparty/doctrine/dbal/src/Connection.php","line":416,"function":"getDatabasePlatformVersion","class":"Doctrine\\DBAL\\Connection","type":"->","args":[]},{"file":"/var/www/html/3rdparty/doctrine/dbal/src/Connection.php","line":323,"function":"detectDatabasePlatform","class":"Doctrine\\DBAL\\Connection","type":"->","args":[]},{"file":"/var/www/html/lib/private/DB/Connection.php","line":946,"function":"getDatabasePlatform","class":"Doctrine\\DBAL\\Connection","type":"->","args":[]},{"file":"/var/www/html/lib/private/DB/ConnectionAdapter.php","line":277,"function":"getDatabaseProvider","class":"OC\\DB\\Connection","type":"->","args":[false]},{"file":"/var/www/html/lib/private/DB/QueryBuilder/QueryBuilder.php","line":85,"function":"getDatabaseProvider","class":"OC\\DB\\ConnectionAdapter","type":"->","args":[]},{"file":"/var/www/html/lib/private/User/Database.php","line":397,"function":"expr","class":"OC\\DB\\QueryBuilder\\QueryBuilder","type":"->","args":[]},{"file":"/var/www/html/lib/private/User/Database.php","line":466,"function":"loadUser","class":"OC\\User\\Database","type":"->","args":["admin"]},{"file":"/var/www/html/lib/private/User/Manager.php","line":154,"function":"userExists","class":"OC\\User\\Database","type":"->","args":["admin"]},{"file":"/var/www/html/lib/private/User/Session.php","line":187,"function":"get","class":"OC\\User\\Manager","type":"->","args":["admin"]},{"file":"/var/www/html/lib/private/User/Session.php","line":229,"function":"getUser","class":"OC\\User\\Session","type":"->","args":[]},{"file":"/var/www/html/lib/base.php","line":1127,"function":"isLoggedIn","class":"OC\\User\\Session","type":"->","args":[]},{"file":"/var/www/html/index.php","line":25,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/var/www/html/lib/private/DB/Connection.php","Line":235,"message":"Failed to connect to the database: An exception occurred in the driver: SQLSTATE[08006] [7] connection to server on socket \"/run/postgresql/.s.PGSQL.5432\" failed: FATAL:  remaining connection slots are reserved for roles with the SUPERUSER attribute","CustomMessage":"Failed to connect to the database: An exception occurred in the driver: SQLSTATE[08006] [7] connection to server on socket \"/run/postgresql/.s.PGSQL.5432\" failed: FATAL:  remaining connection slots are reserved for roles with the SUPERUSER attribute"},"id":"6adbc5dc1a013"}

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