refactor(pag): Use fallocate as the primary method for extending a file

- This should eliminate double writes of pages when file is extended.
- If fallocate is not supported by filesystem fallback to the old method of writing zeroes to the file.

Author: Artyom Ivanov

src/jrd/nbak.cpp

@@ -389,10 +389,12 @@ bool BackupManager::extendDatabase(thread_db* tdbb)
 	if (maxAllocPage >= maxPage)
 		return true;
 
-	if (!pgSpace->extend(tdbb, maxPage, true))
-		return false;
-
+	const auto extension_result = pgSpace->extend(tdbb, maxPage, true);
 	maxAllocPage = pgSpace->maxAlloc();
+	if (extension_result.success && maxAllocPage > maxPage)
+		return true;
+
+	// Fast file extension not succeeded for some reason, try file extension via direct file writes.
 	while (maxAllocPage < maxPage)
 	{
 		const USHORT ret = PIO_init_data(tdbb, pgSpace->file, tdbb->tdbb_status_vector,

src/jrd/os/pio_proto.h

@@ -40,12 +40,13 @@ void	PIO_close(Jrd::jrd_file*);
 Jrd::jrd_file*	PIO_create(Jrd::thread_db*, const Firebird::PathName&,
 							const bool, const bool);
 bool	PIO_expand(const TEXT*, USHORT, TEXT*, FB_SIZE_T);
-void	PIO_extend(Jrd::thread_db*, Jrd::jrd_file*, const ULONG, const USHORT);
+bool	PIO_fast_extension_is_supported(const Jrd::jrd_file& file) noexcept;
+bool	PIO_extend(Jrd::thread_db* tdbb, Jrd::jrd_file* file, ULONG extPages, USHORT pageSize);
 void	PIO_flush(Jrd::thread_db*, Jrd::jrd_file*);
 void	PIO_force_write(Jrd::jrd_file*, const bool);
 ULONG	PIO_get_number_of_pages(const Jrd::jrd_file*, const USHORT);
 bool	PIO_header(Jrd::thread_db*, UCHAR*, unsigned);
-USHORT	PIO_init_data(Jrd::thread_db*, Jrd::jrd_file*, Jrd::FbStatusVector*, ULONG, USHORT);
+USHORT	PIO_init_data(Jrd::thread_db* tdbb, Jrd::jrd_file* file, Jrd::FbStatusVector* status_vector, ULONG startPage, USHORT initPages);
 Jrd::jrd_file*	PIO_open(Jrd::thread_db*, const Firebird::PathName&,
 						 const Firebird::PathName&);
 bool	PIO_read(Jrd::thread_db*, Jrd::jrd_file*, Jrd::BufferDesc*, Ods::pag*, Jrd::FbStatusVector*);

src/jrd/os/posix/unix.cpp

@@ -299,7 +299,19 @@ bool PIO_expand(const TEXT* file_name, USHORT file_length, TEXT* expanded_name,
 }
 
 
-void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USHORT pageSize)
+bool PIO_fast_extension_is_supported(const Jrd::jrd_file& file) noexcept
+{
+#if defined(HAVE_LINUX_FALLOC_H) && defined(HAVE_FALLOCATE)
+	return file.fil_flags & FIL_no_fast_extend
+		? false
+		: true;
+#else
+	return false;
+#endif
+}
+
+
+bool PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USHORT pageSize)
 {
 /**************************************
  *
@@ -317,8 +329,8 @@ void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USH
 
 	EngineCheckout cout(tdbb, FB_FUNCTION, EngineCheckout::UNNECESSARY);
 
-	if (file->fil_flags & FIL_no_fast_extend)
-		return;
+	if (!PIO_fast_extension_is_supported(*file))
+		return false;
 
 	const ULONG filePages = PIO_get_number_of_pages(file, pageSize);
 	const ULONG extendBy = MIN(MAX_ULONG - filePages, extPages);
@@ -341,7 +353,7 @@ void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USH
 			unix_error("fallocate", file, isc_io_write_err);
 
 		file->fil_flags |= FIL_no_fast_extend;
-		return;
+		return false;
 	}
 
 	if (r == IO_RETRY)
@@ -352,12 +364,12 @@ void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USH
 #endif
 		unix_error("fallocate_retry", file, isc_io_write_err);
 	}
+
+	return true;
 #else
 	file->fil_flags |= FIL_no_fast_extend;
+	return false;
 #endif // fallocate present
-
-	// not implemented
-	return;
 }
 
 

src/jrd/os/win32/winnt.cpp

@@ -215,7 +215,13 @@ bool PIO_expand(const TEXT* file_name, USHORT file_length, TEXT* expanded_name,
 }
 
 
-void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USHORT pageSize)
+bool PIO_fast_extension_is_supported(const Jrd::jrd_file& file) noexcept
+{
+	return true;
+}
+
+
+bool PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USHORT pageSize)
 {
 /**************************************
  *
@@ -238,7 +244,7 @@ void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USH
 
 	// if file have no extend lock it is better to not extend file than corrupt it
 	if (!file->fil_ext_lock)
-		return;
+		return false;
 
 	EngineCheckout cout(tdbb, FB_FUNCTION, EngineCheckout::UNNECESSARY);
 	FileExtendLockGuard extLock(file->fil_ext_lock, true);
@@ -257,6 +263,8 @@ void PIO_extend(thread_db* tdbb, jrd_file* file, const ULONG extPages, const USH
 
 	if (!SetEndOfFile(hFile))
 		nt_error("SetEndOfFile", file, isc_io_write_err, NULL);
+
+	return true;
 }