diff --git a/server/main-api/Cargo.toml b/server/main-api/Cargo.toml
index 6500d5d81..30cbc7e05 100644
--- a/server/main-api/Cargo.toml
+++ b/server/main-api/Cargo.toml
@@ -69,7 +69,8 @@ actix-governor = { version = "0.5.0", features = ["logger"] }
 tempfile = "3.10.1"
 base64 = "0.22.1"
 time = "0.3.36"
-polars = { git = "https://github.com/CommanderStorm/polars.git", branch = "serialisation-experiment", features = ["parquet", "serde", "dtype-full"] }
+polars = { version = "0.41.3", features = ["parquet", "dtype-struct"] }
+#polars = { git = "https://github.com/CommanderStorm/polars.git", branch = "serialisation-experiment", features = ["parquet", "serde", "dtype-full"] }
 
 [dev-dependencies]
 insta = { version = "1.39.0", features = ["yaml", "json", "redactions"] }
diff --git a/server/main-api/src/setup/database/data.rs b/server/main-api/src/setup/database/data.rs
index ca8258ee2..efc9754db 100644
--- a/server/main-api/src/setup/database/data.rs
+++ b/server/main-api/src/setup/database/data.rs
@@ -125,28 +125,19 @@ impl DelocalisedValues {
     }
 }
 #[tracing::instrument]
-pub async fn download_updates() -> Result<LimitedVec<DelocalisedValues>, crate::BoxedError> {
+pub async fn download_updates(
+    keys_which_need_updating: &LimitedVec<String>,
+) -> Result<LimitedVec<DelocalisedValues>, crate::BoxedError> {
     let cdn_url = std::env::var("CDN_URL").unwrap_or_else(|_| "https://nav.tum.de/cdn".to_string());
-    let body = reqwest::get(format!("{cdn_url}/api_data.parquet"))
+    let tasks = reqwest::get(format!("{cdn_url}/api_data.json"))
         .await?
-        .error_for_status()?
-        .bytes()
-        .await?;
-    let mut file = tempfile()?;
-    file.write_all(&body)?;
-    let df = ParquetReader::new(&mut file).finish().unwrap();
-    let mut vals = Vec::<DelocalisedValues>::new();
-    let col_names = df.get_column_names().clone();
-    for index in 0..df.get_columns()[0].len() {
-        let row = df.get_row(index)?;
-        let mut hm = HashMap::new();
-        for (i, a) in row.0.into_iter().enumerate() {
-            let v = serde_json::to_value(a)?;
-            hm.insert(col_names[i].to_string(), v);
-        }
-        vals.push(DelocalisedValues::from(hm));
-    }
-    Ok(LimitedVec(vals))
+        .json::<Vec<HashMap<String, Value>>>()
+        .await?
+        .into_iter()
+        .map(DelocalisedValues::from)
+        .filter(|d| keys_which_need_updating.0.contains(&d.key))
+        .collect::<LimitedVec<DelocalisedValues>>();
+    Ok(tasks)
 }
 #[tracing::instrument(skip(tx))]
 pub(super) async fn load_all_to_db(
@@ -159,7 +150,7 @@ pub(super) async fn load_all_to_db(
     Ok(())
 }
 #[tracing::instrument]
-pub async fn download_status() -> Result<LimitedVec<(String, i64)>, crate::BoxedError> {
+pub async fn download_status() -> Result<(LimitedVec<String>,LimitedVec<i64>), crate::BoxedError> {
     let cdn_url = std::env::var("CDN_URL").unwrap_or_else(|_| "https://nav.tum.de/cdn".to_string());
     let body = reqwest::get(format!("{cdn_url}/status_data.parquet"))
         .await?
@@ -170,14 +161,8 @@ pub async fn download_status() -> Result<LimitedVec<(String, i64)>, crate::Boxed
     file.write_all(&body)?;
     let df = ParquetReader::new(&mut file).finish().unwrap();
     let id_col = Vec::from(df.column("id")?.str()?);
-    let hash_col = Vec::from(df.column("id")?.i64()?);
-    let tasks = id_col
-        .into_iter()
-        .zip(hash_col)
-        .flat_map(|(id, hash)| match (id, hash) {
-            (Some(id), Some(hash)) => Some((id.to_string(), hash)),
-            _ => None,
-        })
-        .collect();
-    Ok(LimitedVec(tasks))
+    let id_col=id_col.into_iter().filter_map(|s| s.map(String::from)).collect();
+    let hash_col = Vec::from(df.column("hash")?.i64()?);
+    let hash_col = hash_col.into_iter().flatten().collect();
+    Ok((LimitedVec(id_col), LimitedVec(hash_col)))
 }
diff --git a/server/main-api/src/setup/database/mod.rs b/server/main-api/src/setup/database/mod.rs
index 5d92ebedb..9f18d4439 100644
--- a/server/main-api/src/setup/database/mod.rs
+++ b/server/main-api/src/setup/database/mod.rs
@@ -1,4 +1,4 @@
-use tracing::{debug, debug_span, info};
+use tracing::{debug, debug_span, info, info_span};
 
 use crate::limited::vec::LimitedVec;
 
@@ -14,13 +14,22 @@ pub async fn setup(pool: &sqlx::PgPool) -> Result<(), crate::BoxedError> {
 }
 #[tracing::instrument(skip(pool))]
 pub async fn load_data(pool: &sqlx::PgPool) -> Result<(), crate::BoxedError> {
+    let (new_keys,new_hashes) = data::download_status().await?;
     {
-        let data = data::download_updates().await?;
+        let _ = info_span!("deleting old data").enter();
+        let mut tx = pool.begin().await?;
+        cleanup_deleted(&new_keys, &mut tx).await?;
+        tx.commit().await?;
+    }
+    let keys_which_need_updating =
+        find_keys_which_need_updating(pool, &new_keys, &new_hashes).await?;
+    if !keys_which_need_updating.is_empty() {
+        let _ = info_span!("loading changed data").enter();
+        let data = data::download_updates(&keys_which_need_updating).await?;
         let mut tx = pool.begin().await?;
         data::load_all_to_db(data, &mut tx).await?;
         tx.commit().await?;
     }
-
     {
         let aliases = alias::download_updates().await?;
         let mut tx = pool.begin().await?;