[jira] [Resolved] (IMPALA-8312) Alter database operations have race condition

["Vihang Karajgaonkar (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-8312?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vihang Karajgaonkar resolved IMPALA-8312.
-----------------------------------------
       Resolution: Fixed
    Fix Version/s: Impala 3.3.0

> Alter database operations have race condition
> ---------------------------------------------
>
>                 Key: IMPALA-8312
>                 URL: https://issues.apache.org/jira/browse/IMPALA-8312
>             Project: IMPALA
>          Issue Type: Bug
>            Reporter: Vihang Karajgaonkar
>            Assignee: Vihang Karajgaonkar
>            Priority: Major
>             Fix For: Impala 3.3.0
>
>
> There are currently two {{alter database}} operations seen in {{CatalogOpExecutor}} although I only see one of them documented which is a separate issue.
> Consider the following snippet for {{alter database set owner}} operation.
> {code}
>   private void alterDatabaseSetOwner(String dbName, TAlterDbSetOwnerParams params,
>       TDdlExecResponse response) throws ImpalaException {
>     Db db = catalog_.getDb(dbName);
>     if (db == null) {
>       throw new CatalogException("Database: " + dbName + " does not exist.");
>     }
>     Preconditions.checkNotNull(params.owner_name);
>     Preconditions.checkNotNull(params.owner_type);
>     synchronized (metastoreDdlLock_) {
>       Database msDb = db.getMetaStoreDb();
>       String originalOwnerName = msDb.getOwnerName();
>       PrincipalType originalOwnerType = msDb.getOwnerType();
>       msDb.setOwnerName(params.owner_name);
>       msDb.setOwnerType(PrincipalType.valueOf(params.owner_type.name()));
>       try {
>         applyAlterDatabase(db);
>       } catch (ImpalaRuntimeException e) {
>         msDb.setOwnerName(originalOwnerName);
>         msDb.setOwnerType(originalOwnerType);
>         throw e;
>       }
>       updateOwnerPrivileges(db.getName(), /* tableName */ null, params.server_name,
>           originalOwnerName, originalOwnerType, db.getMetaStoreDb().getOwnerName(),
>           db.getMetaStoreDb().getOwnerType(), response);
>     }
>     addDbToCatalogUpdate(db, response.result);
>     addSummary(response, "Updated database.");
>   }
> {code}
> If you notice above, it takes a lock on {{metastoreDdlLock_}} but does not take a write lock on catalogVersion before altering the metastore db object in-place. This can lead to race conditions between a reader and writer thread. For example, it is possible that the thread which is reading {{msDb}} object can see new value of owner but a old value of owner type.
> The same problem applies to the alterCommentOnDb method below
> {code}
>   private void alterCommentOnDb(String dbName, String comment, TDdlExecResponse response)
>       throws ImpalaRuntimeException, CatalogException {
>     Db db = catalog_.getDb(dbName);
>     if (db == null) {
>       throw new CatalogException("Database: " + dbName + " does not exist.");
>     }
>     synchronized (metastoreDdlLock_) {
>       Database msDb = db.getMetaStoreDb();
>       String originalComment = msDb.getDescription();
>       msDb.setDescription(comment);
>       try {
>         applyAlterDatabase(db);
>       } catch (ImpalaRuntimeException e) {
>         msDb.setDescription(originalComment);
>         throw e;
>       }
>     }
>     addDbToCatalogUpdate(db, response.result);
>     addSummary(response, "Updated database.");
>   }
> {code}



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