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LedgerTxn: audit shouldUpdateLastModified usage in read-only scenarios #3800

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marta-lokhova opened this issue Jun 28, 2023 · 1 comment · May be fixed by #4471
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LedgerTxn: audit shouldUpdateLastModified usage in read-only scenarios #3800

marta-lokhova opened this issue Jun 28, 2023 · 1 comment · May be fixed by #4471
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marta-lokhova commented Jun 28, 2023 •
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It appears that LedgerTxn's flag shouldUpdateLastModified is used inconsistently across the codebase (we now use LedgerTxn a lot more often to load the network config), as sometimes it's set to true and sometimes it's false:

stellar-core/src/herder/TransactionQueue.cpp

Line 1243 in e38ee72

LedgerTxn ltx(mApp.getLedgerTxnRoot(), false,

stellar-core/src/herder/TxQueueLimiter.cpp

Line 128 in e38ee72

LedgerTxn ltx(mApp.getLedgerTxnRoot(), /* shouldUpdateLastModified */ true,

stellar-core/src/ledger/LedgerManagerImpl.cpp

Line 1138 in e38ee72

LedgerTxn ltx(rootLtx, false,

This should not matter for read-only cases, where we do things like

{
        LedgerTxn ltx(mApp.getLedgerTxnRoot(), false,
                      TransactionMode::READ_ONLY_WITHOUT_SQL_TXN);
        auto const& conf = mApp.getLedgerManager().getSorobanNetworkConfig(ltx);
        ... do something with conf...
        ... end of scope, automatic ltx rollback...
}

but in general, this is a footgun that should be fixed. We should audit the usage and see if the flag can be removed (i.e. the condition is always true). If the flag is needed for tests only, we can have a special constructor behind BUILD_TESTS macro.
@marta-lokhova marta-lokhova mentioned this issue Oct 23, 2023
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This issue will be closed by implementing #4315

@marta-lokhova marta-lokhova mentioned this issue Aug 16, 2024
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github-merge-queue bot pushed a commit that referenced this issue Sep 11, 2024
@dmkozh
Switch read-only LedgerTxn to BucketList snapshots (#4431)
fbb53d8 
Resolves #4315 and
#3800 This PR
automatically switches overlay/herder to using BucketListDB snapshots
instead of LedgerTxn.

This change introduces a single "read-only ledger state snapshot"
interface, which supports both SQL (via LedgerTxn) and BucketListDB
snapshots. A unified interface avoids invasive changes to the rest of
the codebase to support both snapshot types, and allows to have a
centralized validation flow for both overlay and apply time.

A notable change is the removal of nested LegderTxn in validation paths,
and using loadWithoutRecord instead in newer protocols. This creates a
stronger invariant that validation flow is only meant to be accessing
read-only version of the ledger, and prevents it from making
modifications by accident. Note that nested LedgerTxn is preserved for
older buggy versions of the protocol (making the code a bit uglier than
I would have preferred, I'm open to ideas on simplifying/refactoring old
protocol logic out of the critical path).
@marta-lokhova marta-lokhova linked a pull request Sep 18, 2024 that will close this issue
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Cleanup apply and validation flows marta-lokhova/stellar-core
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