Use Arrow Schema instead of custom schema type. (#94)

trueleo · web-flow · commit a44b530667a3 · 2022-09-07T17:10:43.000+05:30
Replace custom schema type with arrow schema wrapped in Option. 
If metadata was able to load a schema then it will be of Some variant, 
in case there is no schema ( new stream ) then the None variant will 
be used. This reduces number of times serialisation to schema happens 
and this schema will be directly passed on to future event processing 
and queries.
diff --git a/server/src/event.rs b/server/src/event.rs
@@ -17,6 +17,7 @@
  *
  */
 use datafusion::arrow;
+use datafusion::arrow::datatypes::Schema;
 use datafusion::arrow::json;
 use datafusion::arrow::json::reader::infer_json_schema;
 use datafusion::arrow::record_batch::RecordBatch;
@@ -41,10 +42,6 @@ pub struct Event {
 }
 
 // Events holds the schema related to a each event for a single log stream
-pub struct Schema {
-    pub arrow_schema: arrow::datatypes::Schema,
-    pub string_schema: String,
-}
 
 impl Event {
     fn data_file_path(&self) -> String {
@@ -62,31 +59,29 @@ impl Event {
         &self,
         storage: &impl ObjectStorage,
     ) -> Result<response::EventResponse, Error> {
-        let Schema {
-            arrow_schema,
-            string_schema,
-        } = self.infer_schema().map_err(|e| {
+        let inferred_schema = self.infer_schema().map_err(|e| {
             error!("Failed to infer schema for event. {:?}", e);
             e
         })?;
 
-        let event = self.get_reader(arrow_schema);
+        let event = self.get_reader(inferred_schema.clone());
         let size = self.body_size();
 
         let stream_schema = metadata::STREAM_INFO.schema(&self.stream_name)?;
-        let is_first_event = stream_schema.is_empty();
-        // if stream schema is empty then it is first event.
-        let compressed_size = if is_first_event {
-            // process first event and store schema in obect store
-            self.process_first_event(event, string_schema.clone(), storage)
-                .await?
-        } else {
+        let is_first_event = stream_schema.is_none();
+
+        let compressed_size = if let Some(existing_schema) = stream_schema {
             // validate schema before processing the event
-            if stream_schema != string_schema {
+            if existing_schema != inferred_schema {
                 return Err(Error::SchemaMismatch(self.stream_name.clone()));
             } else {
                 self.process_event(event)?
             }
+        } else {
+            // if stream schema is none then it is first event,
+            // process first event and store schema in obect store
+            self.process_first_event(event, inferred_schema, storage)
+                .await?
         };
 
         if let Err(e) = metadata::STREAM_INFO.update_stats(&self.stream_name, size, compressed_size)
@@ -116,7 +111,7 @@ impl Event {
     async fn process_first_event<R: std::io::Read>(
         &self,
         mut event: json::Reader<R>,
-        string_schema: String,
+        schema: Schema,
         storage: &impl ObjectStorage,
     ) -> Result<u64, Error> {
         let rb = event.next()?.ok_or(Error::MissingRecord)?;
@@ -126,8 +121,9 @@ impl Event {
 
         // Put the inferred schema to object store
         let stream_name = &self.stream_name;
+
         storage
-            .put_schema(stream_name.clone(), string_schema.clone())
+            .put_schema(stream_name.clone(), &schema)
             .await
             .map_err(|e| response::EventError {
                 msg: format!(
@@ -138,7 +134,7 @@ impl Event {
 
         // set the schema in memory for this stream
         metadata::STREAM_INFO
-            .set_schema(self.stream_name.clone(), string_schema)
+            .set_schema(&self.stream_name, schema)
             .map_err(|e| response::EventError {
                 msg: format!(
                     "Failed to set schema for log stream {} due to err: {}",
@@ -180,12 +176,8 @@ impl Event {
         let reader = self.body.as_bytes();
         let mut buf_reader = BufReader::new(reader);
         let inferred_schema = infer_json_schema(&mut buf_reader, None)?;
-        let str_inferred_schema = serde_json::to_string(&inferred_schema)?;
 
-        Ok(Schema {
-            arrow_schema: inferred_schema,
-            string_schema: str_inferred_schema,
-        })
+        Ok(inferred_schema)
     }
 
     fn get_reader(&self, arrow_schema: arrow::datatypes::Schema) -> json::Reader<&[u8]> {
@@ -206,11 +198,8 @@ impl Event {
         let parquet_path = self.data_file_path();
         let parquet_file = fs::File::create(&parquet_path)?;
         let props = WriterProperties::builder().build();
-        let mut writer = ArrowWriter::try_new(
-            parquet_file,
-            Arc::new(self.infer_schema()?.arrow_schema),
-            Some(props),
-        )?;
+        let mut writer =
+            ArrowWriter::try_new(parquet_file, Arc::new(self.infer_schema()?), Some(props))?;
         writer.write(&rb)?;
         writer.close()?;
 
diff --git a/server/src/handlers/logstream.rs b/server/src/handlers/logstream.rs
@@ -92,25 +92,24 @@ pub async fn schema(req: HttpRequest) -> HttpResponse {
 
     match metadata::STREAM_INFO.schema(&stream_name) {
         Ok(schema) => response::ServerResponse {
-            msg: schema,
+            msg: schema
+                .map(|schema| schema.to_json().to_string())
+                .unwrap_or_default(),
             code: StatusCode::OK,
         }
         .to_http(),
         Err(_) => match S3::new().get_schema(&stream_name).await {
-            Ok(schema) if schema.is_empty() => response::ServerResponse {
+            Ok(None) => response::ServerResponse {
                 msg: "log stream is not initialized, please post an event before fetching schema"
                     .to_string(),
                 code: StatusCode::BAD_REQUEST,
             }
             .to_http(),
-            Ok(schema) => {
-                let buf = schema.as_ref();
-                response::ServerResponse {
-                    msg: String::from_utf8(buf.to_vec()).unwrap(),
-                    code: StatusCode::OK,
-                }
-                .to_http()
+            Ok(Some(schema)) => response::ServerResponse {
+                msg: serde_json::from_value(schema.to_json()).unwrap(),
+                code: StatusCode::OK,
             }
+            .to_http(),
             Err(_) => response::ServerResponse {
                 msg: "failed to get log stream schema, because log stream doesn't exist"
                     .to_string(),
@@ -124,7 +123,7 @@ pub async fn schema(req: HttpRequest) -> HttpResponse {
 pub async fn get_alert(req: HttpRequest) -> HttpResponse {
     let stream_name: String = req.match_info().get("logstream").unwrap().parse().unwrap();
 
-    match metadata::STREAM_INFO.alert(stream_name.clone()) {
+    match metadata::STREAM_INFO.alert(&stream_name) {
         Ok(alerts) => response::ServerResponse {
             msg: serde_json::to_string(&alerts).unwrap(),
             code: StatusCode::OK,
@@ -166,11 +165,9 @@ pub async fn put(req: HttpRequest) -> HttpResponse {
 
     // Proceed to create log stream if it doesn't exist
     if s3.get_schema(&stream_name).await.is_err() {
-        if let Err(e) = metadata::STREAM_INFO.add_stream(
-            stream_name.to_string(),
-            "".to_string(),
-            Default::default(),
-        ) {
+        if let Err(e) =
+            metadata::STREAM_INFO.add_stream(stream_name.to_string(), None, Default::default())
+        {
             return response::ServerResponse {
                 msg: format!(
                     "failed to create log stream {} due to error: {}",
@@ -249,7 +246,7 @@ pub async fn put_alert(req: HttpRequest, body: web::Json<serde_json::Value>) ->
         .to_http();
     }
 
-    if let Err(e) = metadata::STREAM_INFO.set_alert(stream_name.to_string(), alerts) {
+    if let Err(e) = metadata::STREAM_INFO.set_alert(&stream_name, alerts) {
         return response::ServerResponse {
             msg: format!(
                 "failed to set alert configuration for log stream {} due to err: {}",
diff --git a/server/src/metadata.rs b/server/src/metadata.rs
@@ -16,7 +16,7 @@
  *
  */
 
-use bytes::Bytes;
+use datafusion::arrow::datatypes::Schema;
 use lazy_static::lazy_static;
 use log::error;
 use serde::{Deserialize, Serialize};
@@ -30,7 +30,7 @@ use crate::storage::ObjectStorage;
 
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
 pub struct LogStreamMetadata {
-    pub schema: String,
+    pub schema: Option<Schema>,
     pub alerts: Alerts,
     pub stats: Stats,
 }
@@ -85,38 +85,42 @@ impl STREAM_INFO {
         Ok(())
     }
 
-    pub fn set_schema(&self, stream_name: String, schema: String) -> Result<(), Error> {
-        let alerts = self.alert(stream_name.clone())?;
-        self.add_stream(stream_name, schema, alerts)
+    pub fn set_schema(&self, stream_name: &str, schema: Schema) -> Result<(), Error> {
+        let mut map = self.write().unwrap();
+        map.get_mut(stream_name)
+            .ok_or(Error::StreamMetaNotFound(stream_name.to_string()))
+            .map(|metadata| {
+                metadata.schema.replace(schema);
+            })
     }
 
-    pub fn schema(&self, stream_name: &str) -> Result<String, Error> {
+    pub fn schema(&self, stream_name: &str) -> Result<Option<Schema>, Error> {
         let map = self.read().unwrap();
-        let meta = map
-            .get(stream_name)
-            .ok_or(Error::StreamMetaNotFound(stream_name.to_string()))?;
-
-        Ok(meta.schema.clone())
+        map.get(stream_name)
+            .ok_or(Error::StreamMetaNotFound(stream_name.to_string()))
+            .map(|metadata| metadata.schema.to_owned())
     }
 
-    pub fn set_alert(&self, stream_name: String, alerts: Alerts) -> Result<(), Error> {
-        let schema = self.schema(&stream_name)?;
-        self.add_stream(stream_name, schema, alerts)
+    pub fn set_alert(&self, stream_name: &str, alerts: Alerts) -> Result<(), Error> {
+        let mut map = self.write().unwrap();
+        map.get_mut(stream_name)
+            .ok_or(Error::StreamMetaNotFound(stream_name.to_string()))
+            .map(|metadata| {
+                metadata.alerts = alerts;
+            })
     }
 
-    pub fn alert(&self, stream_name: String) -> Result<Alerts, Error> {
+    pub fn alert(&self, stream_name: &str) -> Result<Alerts, Error> {
         let map = self.read().unwrap();
-        let meta = map
-            .get(&stream_name)
-            .ok_or(Error::StreamMetaNotFound(stream_name.to_owned()))?;
-
-        Ok(meta.alerts.clone())
+        map.get(stream_name)
+            .ok_or(Error::StreamMetaNotFound(stream_name.to_owned()))
+            .map(|metadata| metadata.alerts.to_owned())
     }
 
     pub fn add_stream(
         &self,
         stream_name: String,
-        schema: String,
+        schema: Option<Schema>,
         alerts: Alerts,
     ) -> Result<(), Error> {
         let mut map = self.write().unwrap();
@@ -153,8 +157,6 @@ impl STREAM_INFO {
             let schema = storage
                 .get_schema(&stream.name)
                 .await
-                .map_err(|e| e.into())
-                .and_then(parse_string)
                 .map_err(|_| Error::SchemaNotInStore(stream.name.to_owned()))?;
 
             let metadata = LogStreamMetadata {
@@ -191,17 +193,21 @@ impl STREAM_INFO {
     }
 }
 
-fn parse_string(bytes: Bytes) -> Result<String, Error> {
-    String::from_utf8(bytes.to_vec()).map_err(|e| e.into())
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
+    use datafusion::arrow::datatypes::{DataType, Field};
     use maplit::hashmap;
     use rstest::*;
     use serial_test::serial;
 
+    #[fixture]
+    fn schema() -> Schema {
+        let field_a = Field::new("a", DataType::Int64, false);
+        let field_b = Field::new("b", DataType::Boolean, false);
+        Schema::new(vec![field_a, field_b])
+    }
+
     #[rstest]
     #[case::zero(0, 0, 0)]
     #[case::some(1024, 512, 2048)]
@@ -229,25 +235,10 @@ mod tests {
     }
 
     #[rstest]
-    #[case::nonempty_string("Hello world")]
-    #[case::empty_string("")]
-    fn test_parse_string(#[case] string: String) {
-        let bytes = Bytes::from(string);
-        assert!(parse_string(bytes).is_ok())
-    }
-
-    #[test]
-    fn test_bad_parse_string() {
-        let bad: Vec<u8> = vec![195, 40];
-        let bytes = Bytes::from(bad);
-        assert!(parse_string(bytes).is_err());
-    }
-
-    #[rstest]
-    #[case::stream_schema_alert("teststream", "schema")]
-    #[case::stream_only("teststream", "")]
+    #[case::stream_schema_alert("teststream", Some(schema()))]
+    #[case::stream_only("teststream", None)]
     #[serial]
-    fn test_add_stream(#[case] stream_name: String, #[case] schema: String) {
+    fn test_add_stream(#[case] stream_name: String, #[case] schema: Option<Schema>) {
         let alerts = Alerts { alerts: vec![] };
         clear_map();
         STREAM_INFO
@@ -271,11 +262,7 @@ mod tests {
     fn test_delete_stream(#[case] stream_name: String) {
         clear_map();
         STREAM_INFO
-            .add_stream(
-                stream_name.clone(),
-                "".to_string(),
-                Alerts { alerts: vec![] },
-            )
+            .add_stream(stream_name.clone(), None, Alerts { alerts: vec![] })
             .unwrap();
 
         STREAM_INFO.delete_stream(&stream_name).unwrap();
diff --git a/server/src/query.rs b/server/src/query.rs
@@ -17,7 +17,6 @@
  */
 
 use chrono::{DateTime, Utc};
-use datafusion::arrow::datatypes::Schema;
 use datafusion::arrow::record_batch::RecordBatch;
 use datafusion::datasource::file_format::parquet::ParquetFormat;
 use datafusion::datasource::listing::ListingOptions;
@@ -94,13 +93,12 @@ impl Query {
             target_partitions: 1,
         };
 
-        let schema = &STREAM_INFO.schema(&self.stream_name)?;
+        let schema = STREAM_INFO.schema(&self.stream_name)?;
 
-        if schema.is_empty() {
-            return Ok(());
-        }
-
-        let schema: Arc<Schema> = Arc::new(serde_json::from_str(schema)?);
+        let schema = match schema {
+            Some(schema) => Arc::new(schema),
+            None => return Ok(()),
+        };
 
         ctx.register_listing_table(
             &self.stream_name,
diff --git a/server/src/s3.rs b/server/src/s3.rs
diff --git a/server/src/storage.rs b/server/src/storage.rs
