etseidl commented on code in PR #8714:
URL: https://github.com/apache/arrow-rs/pull/8714#discussion_r2467378945
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parquet/src/file/metadata/thrift/mod.rs:
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@@ -669,9 +696,46 @@ fn read_row_group(
Ok(row_group)
}
+/// Extract the metadata index from the footer bytes. `buf` should contain the
entire footer.
+pub(crate) fn get_metadata_index(buf: &[u8]) -> Result<Option<MetaIndex>> {
+ // TODO(ets): need constants to get rid of magic numbers
+ if buf.len() < 13 {
+ return Ok(None);
+ }
+ // check the last 4 bytes to see if we have the full footer or not
+ let magic = &buf[buf.len() - 4..];
+ let buf = if magic == "PAR1".as_bytes() {
+ &buf[0..buf.len() - 8]
+ } else {
+ buf
+ };
+
+ // check for PARI followed by 0.
+ if buf[buf.len() - 1] != 0 {
+ return Ok(None);
+ }
+ let magic = &buf[buf.len() - 5..buf.len() - 1];
+ if magic != "PARI".as_bytes() {
Review Comment:
> Another approach would be to place it right before the current metadata
The advantage of using field 32767 is that it's already included in the
footer length. No changes necessary to code used to fetch the footer in as few
GETs as possible. The footer just gets a bit larger.
Now down the road, if the community decides an index is good enough and we
don't need a complete rewrite of the metadata, there would be a need for a more
permanent solution, which likely would involve tucking it in above the footer.
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