mempool: Remove -persistmempoolv1 option #36294

1. 
   fjahr commented at 7:27 AM on September 18, 2026: contributor

   -persistmempoolv1 was added in #28207 as a temporary option to allow downgrading to v26 and earlier, which can't read the XOR'ed mempool.dat. v26 has now been EOL for a while. So any version this option could help downgrade to is unsupported now. It seems ready for removal. I don't think this requires an additional deprecation cycle since the feature is useless for any maintained version and docs have always stated that this was a "temporary option that will be removed in the future".

   Reading v1 files is still supported, so upgrading directly from an old version keeps the persisted mempool.

   mempool_compatibility.py now uses v28.2 as the old node, the oldest release in get_previous_releases.py that writes the current format.

2. DrahtBot added the label Mempool on Sep 18, 2026
3. 
   DrahtBot commented at 7:27 AM on September 18, 2026: contributor

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   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36294.

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4. in test/functional/mempool_compatibility.py:31 in 0dc5253539

     27 | @@ -28,7 +28,7 @@ def skip_test_if_missing_module(self):
     28 |  
     29 |      def setup_network(self):
     30 |          self.add_nodes(self.num_nodes, versions=[
     31 | -            200100,  # Last release without unbroadcast serialization and without XOR
     32 | +            280200,  # Oldest available release with the current (XOR) mempool.dat format
   

   ---

   ---

   

   maflcko commented at 8:29 AM on September 18, 2026:

   huh? Shouldn't this set -persistmempoolv1=1, so that the reading path is still covered?

   Otherwise you are removing coverage (see corecheck)

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   fjahr commented at 9:05 AM on September 18, 2026:

   Right, I got confused here. Added the option and also a comment making the coverage explicit where it happens.

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   maflcko commented at 11:35 AM on September 18, 2026:

   This still drops coverage for LogInfo("Failed to deserialize mempool data on file: %s. Continuing anyway.\n", e.what());, but I guess the coverage there was only implicit (due to missing unbroadcast set), and we don't really care about it anyway?

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   fjahr commented at 12:41 PM on September 19, 2026:

   Right, since we didn't have an explicit check for it, it seems like this coverage was mostly incidental. But some general coverage of a failing import on a malformed mempool file seems like a good idea, so I added that in a separate commit and put it into mempool_persist.py since that seems a more fitting place.

5. maflcko approved
6. 
   maflcko commented at 8:30 AM on September 18, 2026: member

   lgtm. Seems fine. If anyone really wanted to write this, they can just use a previous release and do a start-stop with `-persistmempoolv1=1

   But the test patch looks broken

7. maflcko added this to the milestone 33.0 on Sep 18, 2026
8. fjahr force-pushed on Sep 18, 2026
9. in test/functional/mempool_compatibility.py:32 in 6e0bfbb591

     29 |  
     30 |      def setup_network(self):
     31 | -        self.add_nodes(self.num_nodes, versions=[
     32 | -            200100,  # Last release without unbroadcast serialization and without XOR
     33 | +        self.add_nodes(self.num_nodes, extra_args=self.extra_args, versions=[
     34 | +            280200,  # Oldest available release with -persistmempoolv1
   

   ---

   ---

   

   maflcko commented at 11:35 AM on September 18, 2026:

   I think we prefer the last release (aka youngest, not oldest), or the comment should say "Any release with ..."

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   fjahr commented at 12:23 PM on September 19, 2026:

   I changed the version to v31 and updated the comment, though it's going to be stale in a little bit since v32 will still have the option and then that will be the last release with the option. But I am not sure this worth splitting hairs over right now...

10. maflcko approved
11. 
    maflcko commented at 11:36 AM on September 18, 2026: member

    lgtm

12. test: Use v31.0 as old node in mempool_compatibility.py

    Also removes the -nowallet flag because it is unnecessary since the switch to MiniWallet.

    86a31b93d0
13. mempool: Remove -persistmempoolv1 option d1dfdf8276
14. doc: Add release note for -persistmempoolv1 removal 4c01625f79
15. fjahr force-pushed on Sep 19, 2026
16. test: Check that importmempool fails on a malformed mempool.dat 731b89c09b
17. DrahtBot added the label CI failed on Sep 19, 2026
18. DrahtBot removed the label CI failed on Sep 19, 2026

Contributors

fjahrDrahtBotmaflcko

Milestone
33.0