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pingcap · Aug 11, 2022 · b2680db · b2680db
1 parent adc7b4c
commit b2680db
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Showing 2 changed files with 10 additions and 3 deletions.
diff --git a/dbms/src/Storages/Page/V3/BlobStore.cpp b/dbms/src/Storages/Page/V3/BlobStore.cpp
@@ -114,7 +114,14 @@ void BlobStore::registerPaths()
 
 void BlobStore::reloadConfig(const BlobStore::Config & rhs)
 {
-    config.file_limit_size = rhs.file_limit_size;
+    /// Don't reload config.file_limit_size here. Because there may be a potential race between write thread and gc thread.
+    /// For write thread, it will ignore all BlobFile which capacity is larger than config.file_limit_size.
+    /// For gc thread, if the contents of a BlobFile with capacity larger than config.file_limit_size is all removed, it will remove the BlobFile.
+    /// So if you reload config.file_limit_size will a larger value,
+    /// the write thread may see the change and select a BlobFile which capacity is larger than old config.file_limit_size but smaller than new value for write,
+    /// but the gc thread may not see the change and still think the BlobFile's capacity is larger than config.file_limit_size and remove it if all its contents has been removed.
+    /// And this may cause data lose.
+    //    config.file_limit_size = rhs.file_limit_size;
     config.spacemap_type = rhs.spacemap_type;
     config.cached_fd_size = rhs.cached_fd_size;
     config.block_alignment_bytes = rhs.block_alignment_bytes;

diff --git a/dbms/src/Storages/Page/V3/BlobStore.h b/dbms/src/Storages/Page/V3/BlobStore.h
@@ -250,8 +250,6 @@ class BlobStore : private Allocator<false>
                        const WriteLimiterPtr & write_limiter = nullptr,
                        const ReadLimiterPtr & read_limiter = nullptr);
 
-    PageEntriesEdit handleLargeWrite(DB::WriteBatch & wb, const WriteLimiterPtr & write_limiter = nullptr);
-
     PageEntriesEdit write(DB::WriteBatch & wb, const WriteLimiterPtr & write_limiter = nullptr);
 
     void remove(const PageEntriesV3 & del_entries);
@@ -307,6 +305,8 @@ class BlobStore : private Allocator<false>
 private:
 #endif
 
+    PageEntriesEdit handleLargeWrite(DB::WriteBatch & wb, const WriteLimiterPtr & write_limiter = nullptr);
+
     PSDiskDelegatorPtr delegator;
 
     FileProviderPtr file_provider;