statedb: Restore ability to use Changes with WriteTxn#142
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The index refactoring in cd27022 removed the ability to use ChangeIterator.Next with a WriteTxn targeting the table being observed. This was done to avoid having to hold onto the old instance of the tableEntry, but it broke a useful pattern for Changes(): the ability for a component A to write into a table and component B to be able to observe and "augment" the objects created by A. Restore this ability to by keeping a pointer to the old root in the write transaction. Before: BenchmarkDB_WriteTxn_CommitOnly_100Tables-8 1428603 838.6 ns/op 1112 B/op 5 allocs/op BenchmarkDB_WriteTxn_CommitOnly_1Table-8 2391542 503.3 ns/op 224 B/op 5 allocs/op BenchmarkDB_NewWriteTxn-8 2607277 458.1 ns/op 200 B/op 4 allocs/op BenchmarkDB_WriteTxnCommit100-8 1455978 823.8 ns/op 1096 B/op 5 allocs/op After: BenchmarkDB_WriteTxn_CommitOnly_100Tables-8 1239177 962.4 ns/op 1112 B/op 5 allocs/op BenchmarkDB_WriteTxn_CommitOnly_1Table-8 2332510 515.2 ns/op 224 B/op 5 allocs/op BenchmarkDB_NewWriteTxn-8 2566347 468.2 ns/op 200 B/op 4 allocs/op BenchmarkDB_WriteTxnCommit100-8 1452818 892.0 ns/op 1096 B/op 5 allocs/op No practical difference since we keep a pool for writeTxnHandle and thus don't really allocate more memory even though the writeTxnHandle is larger now. The impact this may have is to workloads that have a huge table and churn through all objects and now WriteTxn holds onto both the old root and the new root being prepared and thus do not allow GC to collect old objects. This however seems unlikely to be an issue since we do hold onto the old root via [DB] and only way for constructing lots of potentially garbage objects is to have two tables churning and have the two WriteTxn's hold onto "garbage" of the other table that is no longer reachable via [DB.ReadTxn]. Signed-off-by: Jussi Maki <jussi.maki@isovalent.com>
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dylandreimerink
approved these changes
Feb 9, 2026
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The index refactoring in cd27022 removed the ability to use ChangeIterator.Next with a WriteTxn targeting the table being observed. This was done to avoid having to hold onto the old instance of the tableEntry, but it broke a useful pattern for Changes(): the ability for a component A to write into a table and component B to be able to observe and "augment" the objects created by A.
Restore this ability to by keeping a pointer to the old root in the write transaction.
Before:
After:
No practical difference since we keep a pool for writeTxnHandle and thus don't really allocate more memory even though the writeTxnHandle is larger now. The impact this may have is to workloads that have a huge table and churn through all objects and now WriteTxn holds onto both the old root and the new root being prepared and thus do not allow GC to collect old objects. This however seems unlikely to be an issue since we do hold onto the old root via [DB] and only way for constructing lots of potentially garbage objects is to have two tables churning and have the two WriteTxn's hold onto "garbage" of the other table that is no longer reachable via [DB.ReadTxn].