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# Problem
Suppose our vectored get starts with an inexact materialized page cache
hit ("cached lsn") that is shadowed by a newer image layer image layer.
Like so:
```
<inmemory layers>
+-+ < delta layer
| |
-|-|----- < image layer
| |
| |
-|-|----- < cached lsn for requested key
+_+
```
The correct visitation order is
1. inmemory layers
2. delta layer records in LSN range `[image_layer.lsn,
oldest_inmemory_layer.lsn_range.start)`
3. image layer
However, the vectored get code, when it visits the delta layer, it
(incorrectly!) returns with state `Complete`.
The reason why it returns is that it calls `on_lsn_advanced` with
`self.lsn_range.start`, i.e., the layer's LSN range.
Instead, it should use `lsn_range.start`, i.e., the LSN range from the
correct visitation order listed above.
# Solution
Use `lsn_range.start` instead of `self.lsn_range.start`.
# Refs
discovered by & fixes https://github.com/neondatabase/neon/issues/6967
Co-authored-by: Vlad Lazar <vlad@neon.tech>