[GitHub] [iceberg] anigos commented on a diff in pull request #8194: Core: check location for conflict before creating table

["anigos (via GitHub)" <gi...@apache.org>]

anigos commented on code in PR #8194:
URL: https://github.com/apache/iceberg/pull/8194#discussion_r1283931646


##########
core/src/main/java/org/apache/iceberg/BaseMetastoreCatalog.java:
##########
@@ -192,6 +192,14 @@ public Table create() {
 
       String baseLocation = location != null ? location : defaultWarehouseLocation(identifier);
       tableProperties.putAll(tableOverrideProperties());
+
+      if (Boolean.parseBoolean(tableProperties.get(TableProperties.UNIQUE_LOCATION))) {
+        boolean alreadyExists = ops.io().newInputFile(baseLocation).exists();
+        if (alreadyExists) {
+          throw new AlreadyExistsException("Table location already in use: %s", baseLocation);

Review Comment:
   
   I have thought through this and mostly two cases came to my mind. We may think with this route
   
   1. No database creation should be allowed under an existing database path. It will help a major problem of people creating even databases under existing db path. 
   2. No table creation should be allowed under an existing table path. 
   
   **Case 1**
   
   We have the following information with us which is an existing Table and it's location. 
   
   Say a table's location is `s3://somerandompath/my_database/my_table `
   
   If we make it much simple and try to set the reference path of a table to database level that can help may be. 
   We have various ways of creating iceberg table just via database.tableName, with location etc. This DB path is always a constant path by practice. If someone is trying to create a table under the same location with same name we can just throw the exception that s3://somerandompath/my_database/my_table exists just by looking it's database reference. The uniqueness not necessarily you need from storage file location
   
   ```
   CREATE TABLE prod.db.sample
   USING iceberg
   PARTITIONED BY (part)
   TBLPROPERTIES ('key'='value')
   AS SELECT ...
   ```
   
   OR 
   
   ```
   CREATE TABLE IF NOT EXISTS prod.db.sample (
            id integer,
           ......
          )
          USING ICEBERG 
          LOCATION 
          TBLPROPERTIES (
            'type' 'hive',.......
          )
   ```
   
   
   **Case 2**
   
   Rename table : When we rename a table we don't move files it is a metadata operation. The base path remains same but the table name gets updated. So in this case there is no impact. For unique location we can still look up to the metadata and get all unique paths under db reference. 
   
   
   



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