Customizable locking while database is busy #1156
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…atabase is not available Signed-off-by: DL6ER <[email protected]>
… the entire answer Signed-off-by: DL6ER <[email protected]>
…tially (incl. when forking a TCP worker) Signed-off-by: DL6ER <[email protected]>
Signed-off-by: DL6ER <[email protected]>
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This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there: https://discourse.pi-hole.net/t/behavior-when-database-is-busy/48174/25 |
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Connected web PR: pi-hole/web#1869 |
8 tasks
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Connected doc PR: pi-hole/docs#554 |
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Sounds like a great idea to me. |
dschaper
approved these changes
Aug 23, 2021
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This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there: https://discourse.pi-hole.net/t/pi-hole-ftl-v5-9-web-v5-6-and-core-v5-4-released/49544/1 |
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Closed
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This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there: https://discourse.pi-hole.net/t/pi-hole-allows-blacklisted-queries-through-on-reboot/52312/12 |
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When the gravity database is locked/busy, Pi-hole allows all queries because it has no way of detecting if they should be blocked or not. However, for very large lists and/or on very busy networks and/or on very (!) slow devices, this may open a windows of up to several seconds where undesired queries may get through, ads and unwanted telemetry could be the result.
This PR adds a config option (
REPLY_WHEN_BUSY) to customize what happens to queries while the database is locked:ALLOW- as before, just allow all queries when the database is busyBLOCK- block all queries when the database is busy. This uses the configuredBLOCKINGMODE(defaultNULL)REFUSE- refuse all queries which arrive while the database is busyDROP- just drop the queries, i.e., never reply to them at all.In my opinion, option 4 is the best one because it will typically cause clients to retry the query after some timeout of typically a few seconds. I.e., the DNS resolution will only be delayed but we do never hand out incorrectly either allowed or blocked queries.
REFUSEfirst sounded like a good option, too, however, it turned out that many clients will just immediately retry, causing up to several thousands of queries per second. This does not happen inDROPmode.