[WIP]

[lidezhu]

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[gemini-code-assist]

Code Review

This pull request modifies the GC safety checks to allow the changefeed startTs (or checkpointTs) to be equal to the GC safepoint, rather than requiring it to be strictly greater. It introduces getGCSafepointUpperBound to set the GC barrier at startTs - 1 and updates tests accordingly. The review feedback highlights a critical issue in next-gen mode where setting startTs == gcSafepoint could leave the changefeed unprotected if the barrier is not explicitly set to startTs, and suggests adding assertions in tests to verify the barrier is correctly set at this boundary.

[gemini-code-assist]

In next-gen mode, if SetGCBarrier fails because gcSafepointUpperBound (startTs - 1) is behind the current GC safepoint, and startTs == gcSafepoint, the current implementation simply returns nil (success) without setting any barrier. This leaves the changefeed unprotected, and a subsequent GC run could advance the safepoint past startTs before the changefeed starts and sets its own barrier.

To prevent this potential data loss, we should explicitly set the GC barrier to startTs when startTs == gcSafepoint.

	if err != nil {
		if !errors.IsGCBarrierTSBehindTxnSafePointError(err) {
			return errors.ErrStartTsBeforeGC.GenWithStackByArgs(startTs, gcSafepointUpperBound)
		}
		gcSafepoint, getErr := UnifyGetServiceGCSafepoint(ctx, pdCli, keyspaceID, gcServiceID)
		if getErr != nil {
			return getErr
		}
		if startTs > 0 && startTs < gcSafepoint {
			return errors.ErrStartTsBeforeGC.GenWithStackByArgs(startTs, gcSafepoint)
		}
		if startTs == gcSafepoint {
			_, err = SetGCBarrier(ctx, gcCli, gcServiceID, startTs, time.Duration(ttl)*time.Second)
			if err != nil {
				return errors.Trace(err)
			}
		}
	}

[gemini-code-assist]

We should assert that the GC barrier is actually set and active in PD when startTs == gcSafepoint (boundary condition), rather than just checking that no error is returned.

Suggested change

	err = EnsureChangefeedStartTsSafety(ctx, pdCli,
	"ticdc-creating-",
	0,
	common.NewChangeFeedIDWithName("changefeed-boundary", "default"), TTL, 60)
	require.NoError(t, err)
	err = EnsureChangefeedStartTsSafety(ctx, pdCli,
	"ticdc-creating-",
	0,
	common.NewChangeFeedIDWithName("changefeed-boundary", "default"), TTL, 60)
	require.NoError(t, err)
	require.Equal(t, uint64(60), pdCli.gcBarriers["ticdc-creating-default_changefeed-boundary"])

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