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figure out why & when exactly zeroes past write offset are required & assert it

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This commit is contained in:
Christian Schwarz
2024-03-14 12:04:17 +00:00
parent 91bd729be2
commit 40200b7521
1 changed files with 13 additions and 9 deletions
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pageserver/src/tenant/ephemeral_file.rs
+13 -9
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@@ -131,21 +131,25 @@ impl EphemeralFile {
}
};
} else {
let reads_past_end = read_offset + (PAGE_SZ as u64) <= buffered_offset;
if reads_past_end {
if cfg!(test) {
// tests rely on being able to read zeroes from offsets [buffered_offset, next PAGE_SZ multiple of buffered_offset).
// TODO: assert it's only up to the next PAGE_SZ
} else {
let read_until_offset = read_offset + (PAGE_SZ as u64);
if !(0..buffered_offset).contains(&read_until_offset) {
// The blob_io code relies on the reader allowing reads past
// the end of what was written, up to end of the current PAGE_SZ chunk.
// This is a relict of the past where we would get a pre-zeroed page from the page cache.
//
// DeltaLayer probably has the same issue, not sure why it needs no special treatment.
let nbytes_past_end = read_until_offset.checked_sub(buffered_offset).unwrap();
if nbytes_past_end >= (PAGE_SZ as u64) {
// TODO: treat this as error. Pre-existing issue before this patch.
panic!(
"return IO error: read past end of file: {read_offset:x} {buffered_offset:x}"
"return IO error: read past end of file: read=0x{read_offset:x} buffered=0x{buffered_offset:x} flushed=0x{flushed_offset}"
)
}
}
let buffer: &[u8; Self::TAIL_SZ] = self.file.as_inner().inspect_buffer();
let read_offset_in_buffer = read_offset.checked_sub(flushed_offset).unwrap();
let read_offset_in_buffer = read_offset
.checked_sub(flushed_offset)
.expect("would have taken `if` branch instead of this one");
let read_offset_in_buffer = usize::try_from(read_offset_in_buffer).unwrap();
let page = &buffer[read_offset_in_buffer..(read_offset_in_buffer + PAGE_SZ)];