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[LLM-coded] Fix division by zero #52

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[LLM-coded] Fix division by zero #52

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63a4443
Fix division by zero
antoyo Jul 28, 2026
499c5e8
Fix clippy warnings
antoyo Jul 28, 2026
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50 changes: 44 additions & 6 deletions src/transparent.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -195,7 +195,7 @@ pub fn zstd_enable_transparent<'a>(ctx: &Context) -> anyhow::Result<ToSqlOutput<
r#"select "from"
from pragma_foreign_key_list('{}')
where "table" = '_zstd_dicts'"#,
&new_table_name
new_table_name
);
log::debug!("dict_id_columns query {:?}", query);
db.prepare(&query)?
Expand Down Expand Up @@ -332,7 +332,7 @@ pub fn zstd_enable_transparent<'a>(ctx: &Context) -> anyhow::Result<ToSqlOutput<
db.execute(
&format_sqlite!(
"create index {} on {} ({})",
&format!("{}_idx", &dict_id_column_name),
&format!("{}_idx", dict_id_column_name),
&new_table_name,
&dict_id_column_name
),
Expand Down Expand Up @@ -461,9 +461,9 @@ fn create_or_replace_view(
Ok(format!(
// prepared statement parameters not allowed in view
"zstd_decompress_col({}, {}, {}, {}) as {0}",
&escape_sqlite_identifier(&c.name),
escape_sqlite_identifier(&c.name),
if affinity_is_text { 1 } else { 0 },
&escape_sqlite_identifier(&get_dict_id(&c.name)),
escape_sqlite_identifier(&get_dict_id(&c.name)),
COMPACT
))
} else {
Expand Down Expand Up @@ -807,7 +807,9 @@ fn maintenance_for_todo(
};

let mut total_updated: i64 = 0;
let mut chunk_size = config.incremental_compression_step_bytes / avg_sample_bytes;
// avg_sample_bytes can be zero when every sample of this group is empty (e.g. '' or x''),
// so clamp it to avoid a division by zero
let mut chunk_size = config.incremental_compression_step_bytes / avg_sample_bytes.max(1);
if chunk_size < 1 {
chunk_size = 1;
}
Expand Down Expand Up @@ -883,7 +885,7 @@ fn maintenance_for_todo(
pretty_bytes(todo.total_bytes),
pretty_bytes(total_size_after),
pretty_bytes(avg_sample_bytes),
pretty_bytes(total_size_after / total_count_after),
pretty_bytes(total_size_after / total_count_after.max(1)),
);
}
Ok(total_updated)
Expand Down Expand Up @@ -1252,6 +1254,42 @@ mod tests {
Ok(())
}

/// Regression test: a group where every value is empty has an average sample size of zero,
/// which used to cause a division by zero when computing the chunk size.
#[test]
fn empty_values_do_not_divide_by_zero() -> anyhow::Result<()> {
let db = create_example_db(None, 0)?;

for id in 1..=10 {
db.execute(
"insert into events (id, timestamp, data) values (?, '2020-01-01', '')",
params![id],
)?;
}

db.query_row(
r#"select zstd_enable_transparent(?)"#,
params![r#"{"table": "events", "column": "data", "compression_level": 3, "dict_chooser": "'[nodict]'"}"#],
|_| Ok(())
).context("enable transparent")?;

db.query_row(
"select zstd_incremental_maintenance(9999999, 1)",
params![],
|row| row.get::<_, i64>(0),
)
.context("incremental maintenance")?;

let uncompressed_count: i64 = db.query_row(
"select count(*) from _events_zstd where _data_dict is null",
params![],
|row| row.get(0),
)?;
assert_eq!(uncompressed_count, 0);

Ok(())
}

#[test]
#[should_panic(expected = "another_col (another_col_idx) - used as part of index")]
fn indexed_column_cannot_be_enabled() {
Expand Down