WIP: journal + transactions

I'm not even sure this code works, but I thought it would be lame to lose even *that* amount of code.

CMakeLists.txt

@@ -12,4 +12,7 @@ add_library(YeltsinDB STATIC
         inc/YeltsinDB/constants.h
         inc/YeltsinDB/types.h
         inc/YeltsinDB/macro.h
-        )
+        inc/YeltsinDB/journal.h src/journal.c
+        inc/YeltsinDB/journal/transaction.h src/journal/transaction.c
+        inc/YeltsinDB/journal/transaction_op.h
+        inc/YDB_ext/vec.h inc/YDB_ext/vec.c)

inc/YDB_ext/LICENSE_vec

@@ -0,0 +1,20 @@
+Copyright (c) 2014 rxi
+
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

inc/YDB_ext/vec.c

@@ -0,0 +1,120 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+/**
+ * Copyright (c) 2014 rxi
+ *
+ * This library is free software; you can redistribute it and/or modify it
+ * under the terms of the MIT license. See LICENSE for details.
+ */
+
+#include "vec.h"
+
+
+int vec_expand_(char **data, int *length, int *capacity, int memsz) {
+  if (*length + 1 > *capacity) {
+    void *ptr;
+    int n = (*capacity == 0) ? 1 : *capacity << 1;
+    ptr = realloc(*data, n * memsz);
+    if (ptr == NULL) return -1;
+    *data = ptr;
+    *capacity = n;
+  }
+  return 0;
+}
+
+
+int vec_reserve_(char **data, int *length, int *capacity, int memsz, int n) {
+  (void) length;
+  if (n > *capacity) {
+    void *ptr = realloc(*data, n * memsz);
+    if (ptr == NULL) return -1;
+    *data = ptr;
+    *capacity = n;
+  }
+  return 0;
+}
+
+
+int vec_reserve_po2_(
+  char **data, int *length, int *capacity, int memsz, int n
+) {
+  int n2 = 1;
+  if (n == 0) return 0;
+  while (n2 < n) n2 <<= 1;
+  return vec_reserve_(data, length, capacity, memsz, n2);
+}
+
+
+int vec_compact_(char **data, int *length, int *capacity, int memsz) {
+  if (*length == 0) {
+    free(*data);
+    *data = NULL;
+    *capacity = 0;
+    return 0;
+  } else {
+    void *ptr;
+    int n = *length;
+    ptr = realloc(*data, n * memsz);
+    if (ptr == NULL) return -1;
+    *capacity = n;
+    *data = ptr;
+  }
+  return 0;
+}
+
+
+int vec_insert_(char **data, int *length, int *capacity, int memsz,
+                 int idx
+) {
+  int err = vec_expand_(data, length, capacity, memsz);
+  if (err) return err;
+  memmove(*data + (idx + 1) * memsz,
+          *data + idx * memsz,
+          (*length - idx) * memsz);
+  return 0;
+}
+
+
+void vec_splice_(char **data, int *length, int *capacity, int memsz,
+                 int start, int count
+) {
+  (void) capacity;
+  memmove(*data + start * memsz,
+          *data + (start + count) * memsz,
+          (*length - start - count) * memsz);
+}
+
+
+void vec_swapsplice_(char **data, int *length, int *capacity, int memsz,
+                     int start, int count
+) {
+  (void) capacity;
+  memmove(*data + start * memsz,
+          *data + (*length - count) * memsz,
+          count * memsz);
+}
+
+
+void vec_swap_(char **data, int *length, int *capacity, int memsz,
+               int idx1, int idx2 
+) {
+  unsigned char *a, *b, tmp;
+  int count;
+  (void) length;
+  (void) capacity;
+  if (idx1 == idx2) return;
+  a = (unsigned char*) *data + idx1 * memsz;
+  b = (unsigned char*) *data + idx2 * memsz;
+  count = memsz;
+  while (count--) {
+    tmp = *a;
+    *a = *b;
+    *b = tmp;
+    a++, b++;
+  }
+}
+
+#ifdef __cplusplus
+}
+#endif

inc/YDB_ext/vec.h

@@ -0,0 +1,189 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Copyright (c) 2014 rxi
+ *
+ * This library is free software; you can redistribute it and/or modify it
+ * under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef VEC_H
+#define VEC_H
+
+#include <stdlib.h>
+#include <string.h>
+
+#define VEC_VERSION "0.2.1"
+
+
+#define vec_unpack_(v)\
+  (char**)&(v)->data, &(v)->length, &(v)->capacity, sizeof(*(v)->data)
+
+
+#define vec_t(T)\
+  struct { T *data; int length, capacity; }
+
+
+#define vec_init(v)\
+  memset((v), 0, sizeof(*(v)))
+
+
+#define vec_deinit(v)\
+  ( free((v)->data),\
+    vec_init(v) ) 
+
+
+#define vec_push(v, val)\
+  ( vec_expand_(vec_unpack_(v)) ? -1 :\
+    ((v)->data[(v)->length++] = (val), 0), 0 )
+
+
+#define vec_pop(v)\
+  (v)->data[--(v)->length]
+
+
+#define vec_splice(v, start, count)\
+  ( vec_splice_(vec_unpack_(v), start, count),\
+    (v)->length -= (count) )
+
+
+#define vec_swapsplice(v, start, count)\
+  ( vec_swapsplice_(vec_unpack_(v), start, count),\
+    (v)->length -= (count) )
+
+
+#define vec_insert(v, idx, val)\
+  ( vec_insert_(vec_unpack_(v), idx) ? -1 :\
+    ((v)->data[idx] = (val), 0), (v)->length++, 0 )
+    
+
+#define vec_sort(v, fn)\
+  qsort((v)->data, (v)->length, sizeof(*(v)->data), fn)
+
+
+#define vec_swap(v, idx1, idx2)\
+  vec_swap_(vec_unpack_(v), idx1, idx2)
+
+
+#define vec_truncate(v, len)\
+  ((v)->length = (len) < (v)->length ? (len) : (v)->length)
+
+
+#define vec_clear(v)\
+  ((v)->length = 0)
+
+
+#define vec_first(v)\
+  (v)->data[0]
+
+
+#define vec_last(v)\
+  (v)->data[(v)->length - 1]
+
+
+#define vec_reserve(v, n)\
+  vec_reserve_(vec_unpack_(v), n)
+
+ 
+#define vec_compact(v)\
+  vec_compact_(vec_unpack_(v))
+
+
+#define vec_pusharr(v, arr, count)\
+  do {\
+    int i__, n__ = (count);\
+    if (vec_reserve_po2_(vec_unpack_(v), (v)->length + n__) != 0) break;\
+    for (i__ = 0; i__ < n__; i__++) {\
+      (v)->data[(v)->length++] = (arr)[i__];\
+    }\
+  } while (0)
+
+
+#define vec_extend(v, v2)\
+  vec_pusharr((v), (v2)->data, (v2)->length)
+
+
+#define vec_find(v, val, idx)\
+  do {\
+    for ((idx) = 0; (idx) < (v)->length; (idx)++) {\
+      if ((v)->data[(idx)] == (val)) break;\
+    }\
+    if ((idx) == (v)->length) (idx) = -1;\
+  } while (0)
+
+
+#define vec_remove(v, val)\
+  do {\
+    int idx__;\
+    vec_find(v, val, idx__);\
+    if (idx__ != -1) vec_splice(v, idx__, 1);\
+  } while (0)
+
+
+#define vec_reverse(v)\
+  do {\
+    int i__ = (v)->length / 2;\
+    while (i__--) {\
+      vec_swap((v), i__, (v)->length - (i__ + 1));\
+    }\
+  } while (0)
+
+
+#define vec_foreach(v, var, iter)\
+  if  ( (v)->length > 0 )\
+  for ( (iter) = 0;\
+        (iter) < (v)->length && (((var) = (v)->data[(iter)]), 1);\
+        ++(iter))
+
+
+#define vec_foreach_rev(v, var, iter)\
+  if  ( (v)->length > 0 )\
+  for ( (iter) = (v)->length - 1;\
+        (iter) >= 0 && (((var) = (v)->data[(iter)]), 1);\
+        --(iter))
+
+
+#define vec_foreach_ptr(v, var, iter)\
+  if  ( (v)->length > 0 )\
+  for ( (iter) = 0;\
+        (iter) < (v)->length && (((var) = &(v)->data[(iter)]), 1);\
+        ++(iter))
+
+
+#define vec_foreach_ptr_rev(v, var, iter)\
+  if  ( (v)->length > 0 )\
+  for ( (iter) = (v)->length - 1;\
+        (iter) >= 0 && (((var) = &(v)->data[(iter)]), 1);\
+        --(iter))
+
+
+
+int vec_expand_(char **data, int *length, int *capacity, int memsz);
+int vec_reserve_(char **data, int *length, int *capacity, int memsz, int n);
+int vec_reserve_po2_(char **data, int *length, int *capacity, int memsz,
+                     int n);
+int vec_compact_(char **data, int *length, int *capacity, int memsz);
+int vec_insert_(char **data, int *length, int *capacity, int memsz,
+                int idx);
+void vec_splice_(char **data, int *length, int *capacity, int memsz,
+                 int start, int count);
+void vec_swapsplice_(char **data, int *length, int *capacity, int memsz,
+                     int start, int count);
+void vec_swap_(char **data, int *length, int *capacity, int memsz,
+               int idx1, int idx2);
+
+
+typedef vec_t(void*) vec_void_t;
+typedef vec_t(char*) vec_str_t;
+typedef vec_t(int) vec_int_t;
+typedef vec_t(char) vec_char_t;
+typedef vec_t(float) vec_float_t;
+typedef vec_t(double) vec_double_t;
+
+#endif
+
+#ifdef __cplusplus
+}
+#endif

inc/YeltsinDB/constants.h

@@ -44,4 +44,46 @@ enum YDB_v1_page_offsets {
   YDB_v1_page_prev_offset = YDB_v1_page_next_offset + YDB_v1_page_next_size,
   YDB_v1_page_row_count_offset = YDB_v1_page_prev_offset + YDB_v1_page_prev_size,
   YDB_v1_page_data_offset = YDB_v1_page_row_count_offset + YDB_v1_page_row_count_size,
+};
+
+#define YDB_JRNL_SIGN "JRNL"
+#define YDB_JRNL_SIGN_SIZE (sizeof(YDB_JRNL_SIGN)-1)
+
+enum YDB_jrnl_sizes {
+  YDB_jrnl_first_transaction_size = 8,
+  YDB_jrnl_last_transaction_size = 8,
+  YDB_jrnl_transaction_prev_size = 8,
+  YDB_jrnl_transaction_next_size = 8,
+  YDB_jrnl_transaction_timestamp_size = 8,
+  YDB_jrnl_transaction_flags_size = 1,
+  YDB_jrnl_transaction_op_type_size = 1,
+  YDB_jrnl_transaction_op_datasz_size = 4,
+};
+
+enum YDB_jrnl_offsets {
+  YDB_jrnl_first_transaction_offset = YDB_JRNL_SIGN_SIZE,
+  YDB_jrnl_last_transaction_offset = YDB_jrnl_first_transaction_offset + YDB_jrnl_first_transaction_size,
+  YDB_jrnl_data_offset = YDB_jrnl_last_transaction_offset + YDB_jrnl_last_transaction_size,
+};
+
+enum YDB_jrnl_transaction_offsets {
+  YDB_jrnl_transaction_prev_offset = 0,
+  YDB_jrnl_transaction_next_offset = YDB_jrnl_transaction_prev_offset + YDB_jrnl_transaction_prev_size,
+  YDB_jrnl_transaction_timestamp_offset = YDB_jrnl_transaction_next_offset + YDB_jrnl_transaction_next_size,
+  YDB_jrnl_transaction_flags_offset = YDB_jrnl_transaction_timestamp_offset + YDB_jrnl_transaction_timestamp_size,
+  YDB_jrnl_transaction_data_offset = YDB_jrnl_transaction_flags_offset + YDB_jrnl_transaction_flags_size,
+};
+
+enum YDB_jrnl_transaction_op_offsets {
+  YDB_jrnl_transaction_op_type_offset = 0,
+  YDB_jrnl_transaction_op_datasz_offset = YDB_jrnl_transaction_op_type_offset + YDB_jrnl_transaction_op_type_size,
+  YDB_jrnl_transaction_op_data_offset = YDB_jrnl_transaction_op_datasz_offset + YDB_jrnl_transaction_op_datasz_size,
+};
+
+enum YDB_jrnl_transaction_ops {
+  YDB_jrnl_op_page_alloc = 0x01,
+  YDB_jrnl_op_page_modify = 0x02,
+  YDB_jrnl_op_page_remove = 0x03,
+  YDB_jrnl_op_rollback = 0xFE,
+  YDB_jrnl_op_complete = 0xFF,
 };

inc/YeltsinDB/error_code.h

@@ -70,6 +70,54 @@
  * @brief The addresses of pages are the same.
  */
 #define YDB_ERR_SAME_PAGE_ADDRESS           (-14)
+/**
+ * @brief The transaction is not initialized.
+ */
+#define YDB_ERR_TRANSACTION_NOT_INITIALIZED (-15)
+/**
+ * @brief Transaction operation push failed.
+ */
+#define YDB_ERR_TRANSACTION_OP_PUSH_FAILED  (-16)
+/**
+ * @brief Index of transaction operation is out of range.
+ */
+#define YDB_ERR_TRANSACTION_OP_OUT_OF_RANGE (-17)
+/**
+ * @brief The journal is not initialized.
+ */
+#define YDB_ERR_JOURNAL_NOT_INITIALIZED     (-18)
+/**
+ * @brief The journal is in use.
+ */
+#define YDB_ERR_JOURNAL_IN_USE              (-19)
+/**
+ * @brief The journal is not in use.
+ */
+#define YDB_ERR_JOURNAL_NOT_IN_USE          (-20)
+/**
+ * @brief The journal file does not exist.
+ */
+#define YDB_ERR_JOURNAL_NOT_EXIST           (-21)
+/**
+ * @brief The journal file does already exist.
+ */
+#define YDB_ERR_JOURNAL_EXIST               (-22)
+/**
+ * @brief The journal file is corrupted.
+ */
+#define YDB_ERR_JOURNAL_FILE_CORRUPTED      (-23)
+/**
+ * @brief The journal is not consistent.
+ */
+#define YDB_ERR_JOURNAL_NOT_CONSISTENT      (-24)
+/**
+ * @brief No more transactions left in the journal.
+ */
+#define YDB_ERR_NO_MORE_TRANSACTIONS        (-25)
+/**
+ * @brief The journal is empty.
+ */
+#define YDB_ERR_JOURNAL_EMPTY               (-26)
 /**
  * @brief An unknown error has occurred.
  */

inc/YeltsinDB/journal.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <YeltsinDB/types.h>
+#include <YeltsinDB/journal/transaction.h>
+
+/**
+ * @file journal.h
+ * @todo Doxygen.
+ */
+
+struct __YDB_Journal;
+typedef struct __YDB_Journal YDB_Journal;
+
+YDB_Journal* ydb_journal_init();
+
+void ydb_journal_destroy(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_file_create(YDB_Journal* jrnl, char* path);
+
+YDB_Error ydb_journal_file_open(YDB_Journal* jrnl, char* path);
+
+YDB_Error ydb_journal_file_close(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_file_check_consistency(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_seek_to_begin(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_seek_to_end(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_prev_transaction(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_next_transaction(YDB_Journal* jrnl);
+
+YDB_Error ydb_journal_append_transaction(YDB_Journal* jrnl, YDB_Transaction* transaction);
+
+YDB_Transaction* ydb_journal_get_current_transaction(YDB_Journal* jrnl);
+
+#ifdef __cplusplus
+}
+#endif

inc/YeltsinDB/journal/transaction.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @file journal/transaction.h
+ * @todo Doxygen.
+ */
+
+#include <YeltsinDB/journal/transaction_op.h>
+
+struct __YDB_Transaction;
+typedef struct __YDB_Transaction YDB_Transaction;
+
+/**
+ * @brief Create a new transaction.
+ * @return A transaction instance.
+ */
+YDB_Transaction* ydb_transaction_create();
+
+/**
+ * @brief Destroy a transaction object.
+ * @param t Transaction object.
+ */
+void ydb_transaction_destroy(YDB_Transaction* t);
+
+YDB_Timestamp ydb_transaction_timestamp_get(YDB_Transaction* t);
+
+YDB_Error ydb_transaction_timestamp_set(YDB_Transaction* t, YDB_Timestamp timestamp);
+
+YDB_Flags ydb_transaction_flags_get(YDB_Transaction* t);
+
+YDB_Error ydb_transaction_flags_set(YDB_Transaction* t, YDB_Flags flags);
+
+uint32_t ydb_transaction_ops_size_get(YDB_Transaction* t);
+
+YDB_Error ydb_transaction_push_op(YDB_Transaction* t, YDB_TransactionOp* op);
+
+YDB_Error ydb_transaction_pop_op(YDB_Transaction* t);
+
+YDB_TransactionOp* ydb_transaction_op_at(YDB_Transaction* t, uint32_t index);
+
+YDB_Transaction* ydb_transaction_clone(YDB_Transaction* t);
+
+#ifdef __cplusplus
+}
+#endif

inc/YeltsinDB/journal/transaction_op.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <YeltsinDB/macro.h>
+
+/**
+ * @file journal/transaction_op.h
+ * @todo Doxygen.
+ */
+
+struct __YDB_TransactionOp {
+  YDB_OpCode opcode;
+  YDB_OpDataSize size;
+  void* data;
+};
+typedef struct __YDB_TransactionOp YDB_TransactionOp;
+
+void ydb_transaction_op_destroy(YDB_TransactionOp* op) {
+  free(op->data);
+  free(op);
+}
+
+YDB_TransactionOp* ydb_transaction_op_clone(YDB_TransactionOp* op) {
+  THROW_IF_NULL(op, NULL);
+  YDB_TransactionOp* result = malloc(sizeof(YDB_TransactionOp));
+  result->opcode = op->opcode;
+  result->size = op->size;
+  result->data = malloc(op->size);
+  memcpy(result->data, op->data, op->size);
+  return result;
+}
+
+#ifdef __cplusplus
+}
+#endif

inc/YeltsinDB/types.h

@@ -11,6 +11,13 @@
 typedef int16_t YDB_Error;
 /** @brief YeltsinDB data file offset type. */
 typedef uint64_t YDB_Offset;
-/** */
+/** @brief YeltsinDB page size type. */
 typedef uint16_t YDB_PageSize;
+/** @brief YeltsinDB flags container type. */
 typedef uint8_t YDB_Flags;
+/** @brief YeltsinDB journal operation code type. */
+typedef uint8_t YDB_OpCode;
+/** @brief YeltsinDB Unix timestamp type. */
+typedef int64_t YDB_Timestamp;
+/** @brief YeltsinDB operation data size type. */
+typedef uint32_t YDB_OpDataSize;

inc/YeltsinDB/ydb.h

@@ -135,6 +135,8 @@ YDB_Error ydb_seek_to_begin(YDB_Engine* instance);
  */
 YDB_Error ydb_seek_to_end(YDB_Engine* instance);
 
+YDB_Error ydb_commit_changes(YDB_Engine* instance);
+
 // TODO: rebuild page offsets, etc.
 
 /**

journal_file.md

@@ -3,11 +3,11 @@
 ## Specification
 
 1. `JRNL` file signature (4 bytes)
-2. The offset to the first transaction (8 bytes)
+2. The offset to the first transaction (8 bytes) **(could be 0 if no transactions)**
-3. The offset to the last transaction (8 bytes)
+3. The offset to the last transaction (8 bytes) **(could be 0 if no transactions)**
 4. Transactions
-    1. Previous transaction offset (8 bytes)
+    1. Previous transaction offset (8 bytes) **(could be 0 if the first one)**
-    2. Next transaction offset (8 bytes)
+    2. Next transaction offset (8 bytes) **(could be 0 if the last one)**
     3. Creation date in Unix timestamp format (8 bytes)
     4. Transaction flags (1 byte)
     5. Operations list
@@ -20,12 +20,16 @@
 ### Flags
 
 **TODO**. Now there is the only option -- `JRNL_COMPLETE` on bit 0.
+It means that the transaction was completely written to the storage.
 
 ### Consistency
 
 If the last transaction was not written completely, journal rollback is started.
 That means that it will be cleaned since it has not even been written to storage.
 
+If the incomplete transaction is the only one in journal, the journal file is truncated 
+to 20 bytes and first and last transaction offsets are being nulled.
+
 If the last transaction is complete in journal but not in storage (flag `JRNL_COMPLETE` is 
 not set), redo is being done. That means the transaction starts again since the journal is 
 consistent. 

src/journal.c

@@ -0,0 +1,409 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <YeltsinDB/types.h>
+#include <YeltsinDB/error_code.h>
+#include <YeltsinDB/constants.h>
+#include <YeltsinDB/macro.h>
+#include <YeltsinDB/journal/transaction.h>
+#include <YeltsinDB/journal/transaction_op.h>
+#include <YeltsinDB/journal.h>
+
+struct __YDB_Journal {
+  FILE *fd;
+  YDB_Offset first_transaction_offset;
+  YDB_Offset last_transaction_offset;
+
+  YDB_Offset prev_transaction_offset;
+  YDB_Offset curr_transaction_offset;
+  YDB_Offset next_transaction_offset;
+
+  YDB_Transaction* curr_transaction;
+
+  uint8_t is_consistent;
+  uint8_t in_use;
+};
+
+inline static YDB_Error __ydb_jrnl_truncate_incomplete(YDB_Journal* j, YDB_Offset last_complete_offset) {
+  THROW_IF_NULL(j, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+
+  // The only transaction is incomplete
+  if (last_complete_offset == 0) {
+    j->prev_transaction_offset = 0;
+    j->next_transaction_offset = 0;
+    j->curr_transaction_offset = 0;
+    j->first_transaction_offset = 0;
+    j->last_transaction_offset = 0;
+
+    fseeko(j->fd, YDB_jrnl_first_transaction_offset, SEEK_SET);
+    fwrite(&j->first_transaction_offset, sizeof(YDB_Offset), 1, j->fd);
+    fwrite(&j->last_transaction_offset, sizeof(YDB_Offset), 1, j->fd);
+
+    ftruncate(fileno(j->fd), YDB_jrnl_data_offset);
+    fsync(fileno(j->fd));
+    return YDB_ERR_SUCCESS;
+  }
+
+  fseeko(j->fd, last_complete_offset + YDB_jrnl_transaction_prev_offset, SEEK_SET);
+
+  YDB_Offset prev_offset;
+  fread(&prev_offset, sizeof(YDB_Offset), 1, j->fd);
+  REASSIGN_FROM_LE(prev_offset);
+
+  YDB_Offset next_offset;
+  fread(&next_offset, sizeof(YDB_Offset), 1, j->fd);
+  REASSIGN_FROM_LE(next_offset);
+
+  fseeko(j->fd, last_complete_offset + YDB_jrnl_transaction_next_offset, SEEK_SET);
+  YDB_Offset new_next_offset = 0;
+  fwrite(&new_next_offset, sizeof(YDB_Offset), 1, j->fd);
+
+  j->last_transaction_offset = last_complete_offset;
+  fseeko(j->fd, YDB_jrnl_last_transaction_offset, SEEK_SET);
+  YDB_Offset last_complete_offset_le = TO_LE(last_complete_offset);
+  fwrite(&last_complete_offset_le, sizeof(YDB_Offset), 1, j->fd);
+
+  ftruncate(fileno(j->fd), next_offset);
+  fsync(fileno(j->fd));
+
+  return YDB_ERR_SUCCESS;
+}
+
+inline static YDB_TransactionOp* __ydb_read_op(YDB_Journal* j) {
+  THROW_IF_NULL(j, NULL);
+  YDB_TransactionOp* r = malloc(sizeof(YDB_TransactionOp));
+  fread(&r->opcode, sizeof(YDB_OpCode), 1, j->fd);
+  fread(&r->size, sizeof(YDB_OpDataSize), 1, j->fd);
+  r->data = malloc(r->size);
+  fread(r->data, r->size, 1, j->fd);
+  return r;
+}
+
+inline static YDB_Error __ydb_jrnl_read(YDB_Journal* j, YDB_Offset off) {
+  THROW_IF_NULL(j, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+
+  j->curr_transaction_offset = off;
+  fseeko(j->fd, off, SEEK_SET);
+
+  YDB_Offset prev_offset, next_offset;
+  YDB_Timestamp timestamp;
+  YDB_Flags flags;
+
+  fread(&prev_offset, sizeof(YDB_Offset), 1, j->fd);
+  fread(&next_offset, sizeof(YDB_Offset), 1, j->fd);
+  fread(&timestamp, sizeof(YDB_Timestamp), 1, j->fd);
+  fread(&flags, sizeof(YDB_Flags), 1, j->fd);
+
+  j->prev_transaction_offset = prev_offset;
+  j->next_transaction_offset = next_offset;
+
+  YDB_Transaction* t = ydb_transaction_create();
+  ydb_transaction_timestamp_set(t, timestamp);
+  ydb_transaction_flags_set(t, flags);
+
+  YDB_TransactionOp* op;
+  do {
+    op = __ydb_read_op(j);
+    if (op->opcode != YDB_jrnl_op_complete) {
+      ydb_transaction_push_op(t, op);
+    }
+  } while (op->opcode != YDB_jrnl_op_complete);
+
+  return YDB_ERR_SUCCESS;
+}
+
+YDB_Journal *ydb_journal_init() {
+  YDB_Journal* result = calloc(1, sizeof(YDB_Journal));
+  return result;
+}
+
+void ydb_journal_destroy(YDB_Journal *jrnl) {
+  ydb_journal_file_close(jrnl);
+  free(jrnl);
+}
+
+YDB_Error ydb_journal_file_create(YDB_Journal *jrnl, char *path) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(!jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+
+  if (access(path, F_OK) != -1) {
+    // TODO: Windows does not check W_OK correctly, use other methods.
+    // TODO: if can't read/write, throw other error
+    return YDB_ERR_JOURNAL_EXIST;
+  }
+
+  FILE *f = fopen(path, "wb");
+
+  char tpl[] = YDB_JRNL_SIGN          // File signature
+  "\x00\x00\x00\x00\x00\x00\x00\x00"  // First transaction offset
+  "\x00\x00\x00\x00\x00\x00\x00\x00"; // Last transaction offset
+  fwrite(tpl, sizeof(tpl)-1, 1, f);
+
+  fclose(f);
+
+  return ydb_journal_file_open(jrnl, path);
+}
+
+YDB_Error ydb_journal_file_open(YDB_Journal *jrnl, char *path) {
+  THROW_IF_NULL(jrnl, YDB_ERR_INSTANCE_NOT_INITIALIZED);
+  THROW_IF_NULL(!jrnl->in_use, YDB_ERR_INSTANCE_IN_USE);
+
+  if (access(path, F_OK) == -1) {
+    // TODO: Windows does not check W_OK correctly, use other methods.
+    // TODO: if can't read/write, throw other error
+    return YDB_ERR_JOURNAL_NOT_EXIST;
+  }
+
+  jrnl->fd = fopen(path, "rb+");
+  THROW_IF_NULL(jrnl->fd, YDB_ERR_UNKNOWN); // TODO file open error
+
+  char signature[YDB_JRNL_SIGN_SIZE];
+  fread(signature, 1, YDB_JRNL_SIGN_SIZE, jrnl->fd);
+  int sig_match = memcmp(signature, YDB_JRNL_SIGN, YDB_JRNL_SIGN_SIZE) == 0;
+  if (!sig_match) {
+    return YDB_ERR_JOURNAL_FILE_CORRUPTED;
+  }
+
+  // TODO check for read error
+  fread(&jrnl->first_transaction_offset, sizeof(YDB_Offset), 1, jrnl->fd);
+  REASSIGN_FROM_LE(jrnl->first_transaction_offset);
+  fread(&jrnl->last_transaction_offset, sizeof(YDB_Offset), 1, jrnl->fd);
+  REASSIGN_FROM_LE(jrnl->last_transaction_offset);
+
+  jrnl->in_use = -1;
+  jrnl->curr_transaction_offset = jrnl->first_transaction_offset;
+
+  return ydb_journal_file_check_consistency(jrnl);
+}
+
+YDB_Error ydb_journal_file_close(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+
+  jrnl->first_transaction_offset = 0;
+  jrnl->last_transaction_offset = 0;
+  jrnl->prev_transaction_offset = 0;
+  jrnl->curr_transaction_offset = 0;
+  jrnl->next_transaction_offset = 0;
+  ydb_transaction_destroy(jrnl->curr_transaction);
+  jrnl->curr_transaction = NULL;
+  fclose(jrnl->fd);
+  jrnl->in_use = 0;
+
+  return YDB_ERR_SUCCESS;
+}
+
+YDB_Error ydb_journal_file_check_consistency(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+
+  // Empty journal is always consistent lol
+  if (jrnl->last_transaction_offset == 0) {
+    jrnl->is_consistent = -1;
+    return YDB_ERR_SUCCESS;
+  }
+
+  YDB_Offset last_complete_offset = 0;
+  YDB_Offset prev_offset = 0;
+  YDB_Offset next_offset = 0;
+
+  fseeko(jrnl->fd, jrnl->last_transaction_offset, SEEK_SET);
+  if (fread(&prev_offset, sizeof(YDB_Offset), 1, jrnl->fd) != sizeof(YDB_Offset)) {
+    if (feof(jrnl->fd)) {
+      clearerr(jrnl->fd);
+      perror("Mozhno nenado...\n");
+      abort();
+      // TODO try to find last transaction from begin
+    } else {
+      return YDB_ERR_UNKNOWN; // FIXME
+    }
+  }
+  REASSIGN_FROM_LE(prev_offset);
+
+  last_complete_offset = prev_offset;
+
+  if (fread(&next_offset, sizeof(YDB_Offset), 1, jrnl->fd) != sizeof(YDB_Offset)) {
+    if (feof(jrnl->fd)) {
+      clearerr(jrnl->fd);
+      __ydb_jrnl_truncate_incomplete(jrnl, last_complete_offset);
+      jrnl->is_consistent = -1;
+      return YDB_ERR_SUCCESS;
+    } else {
+      return YDB_ERR_UNKNOWN; // FIXME
+    }
+  }
+  REASSIGN_FROM_LE(next_offset);
+
+  if (next_offset != 0) {
+    perror("Kavo? Ne ponyal shyas...\n");
+    abort(); // Аборт -- это грех, кста
+  }
+
+  fseeko(jrnl->fd, jrnl->last_transaction_offset + YDB_jrnl_transaction_flags_offset, SEEK_SET);
+  if (feof(jrnl->fd)) {
+    __ydb_jrnl_truncate_incomplete(jrnl, last_complete_offset);
+    jrnl->is_consistent = -1;
+    return YDB_ERR_SUCCESS;
+  } else if (ferror(jrnl->fd)) {
+    return YDB_ERR_UNKNOWN; //FIXME
+  }
+
+  YDB_Flags flags = 0;
+  fread(&flags, sizeof(YDB_Flags), 1, jrnl->fd);
+
+  if (flags & 1) { //FIXME magic
+    // A transaction has been written to the storage.
+    return YDB_ERR_SUCCESS;
+  } else {
+    YDB_OpCode op = 0;
+
+    while (op != YDB_jrnl_op_complete) {
+      YDB_OpDataSize size;
+      fread(&op, sizeof(YDB_TransactionOp), 1, jrnl->fd);
+      fread(&size, sizeof(YDB_OpDataSize), 1, jrnl->fd);
+      REASSIGN_FROM_LE(size);
+
+      if (feof(jrnl->fd) || ferror(jrnl->fd)) break;
+      fseeko(jrnl->fd, size, SEEK_CUR);
+    }
+
+    if (op == YDB_jrnl_op_complete) {
+      //fseeko(jrnl->fd, jrnl->last_transaction_offset + YDB_jrnl_transaction_flags_offset, SEEK_SET);
+      //fwrite(flags | 1, sizeof(YDB_Flags), 1, jrnl->fd); //FIXME magic // Also flag should be written when the data in storage is consistent
+      //fsync(fileno(jrnl->fd));
+      jrnl->is_consistent = -1;
+      return YDB_ERR_SUCCESS;
+    }
+    __ydb_jrnl_truncate_incomplete(jrnl, last_complete_offset);
+  }
+
+  jrnl->is_consistent = -1;
+  YDB_Error e = ydb_journal_seek_to_begin(jrnl);
+  if (e == YDB_ERR_SUCCESS || e == YDB_ERR_JOURNAL_EMPTY) {
+    return YDB_ERR_SUCCESS;
+  }
+}
+
+YDB_Error ydb_journal_seek_to_begin(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+  THROW_IF_NULL(jrnl->is_consistent, YDB_ERR_JOURNAL_NOT_CONSISTENT);
+  THROW_IF_NULL(jrnl->first_transaction_offset, YDB_ERR_JOURNAL_EMPTY);
+
+  return __ydb_jrnl_read(jrnl, jrnl->first_transaction_offset);
+}
+
+YDB_Error ydb_journal_seek_to_end(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+  THROW_IF_NULL(jrnl->is_consistent, YDB_ERR_JOURNAL_NOT_CONSISTENT);
+  THROW_IF_NULL(jrnl->last_transaction_offset, YDB_ERR_JOURNAL_EMPTY);
+
+  return __ydb_jrnl_read(jrnl, jrnl->last_transaction_offset);
+}
+
+YDB_Error ydb_journal_prev_transaction(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+  THROW_IF_NULL(jrnl->is_consistent, YDB_ERR_JOURNAL_NOT_CONSISTENT);
+
+  if (jrnl->prev_transaction_offset != 0) {
+    __ydb_jrnl_read(jrnl, jrnl->prev_transaction_offset);
+    return YDB_ERR_SUCCESS;
+  }
+  return YDB_ERR_NO_MORE_TRANSACTIONS;
+}
+
+YDB_Error ydb_journal_next_transaction(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+  THROW_IF_NULL(jrnl->is_consistent, YDB_ERR_JOURNAL_NOT_CONSISTENT);
+
+  if (jrnl->next_transaction_offset != 0) {
+    __ydb_jrnl_read(jrnl, jrnl->prev_transaction_offset);
+    return YDB_ERR_SUCCESS;
+  }
+  return YDB_ERR_NO_MORE_TRANSACTIONS;
+}
+
+YDB_Error ydb_journal_append_transaction(YDB_Journal *jrnl, YDB_Transaction *transaction) {
+  THROW_IF_NULL(jrnl, YDB_ERR_JOURNAL_NOT_INITIALIZED);
+  THROW_IF_NULL(jrnl->in_use, YDB_ERR_JOURNAL_NOT_IN_USE);
+  THROW_IF_NULL(jrnl->is_consistent, YDB_ERR_JOURNAL_NOT_CONSISTENT);
+
+  YDB_Transaction* t = ydb_transaction_clone(transaction);
+
+  fseeko(jrnl->fd, 0, SEEK_END);
+  YDB_Offset file_end = ftello(jrnl->fd);
+  YDB_Offset file_end_le = TO_LE(file_end);
+
+  YDB_Offset prev = jrnl->last_transaction_offset;
+  YDB_Offset prev_le = TO_LE(prev);
+  YDB_Offset next_le = 0;
+  YDB_Timestamp ts_le = TO_LE(ydb_transaction_timestamp_get(t));
+  YDB_Flags flags = ydb_transaction_flags_get(t);
+
+  fseeko(jrnl->fd, file_end, SEEK_SET);
+  fwrite(&prev_le, sizeof(YDB_Offset), 1, jrnl->fd);
+  fwrite(&next_le, sizeof(YDB_Offset), 1, jrnl->fd);
+  fwrite(&ts_le, sizeof(YDB_Timestamp), 1, jrnl->fd);
+  fwrite(&flags, sizeof(YDB_Flags), 1, jrnl->fd);
+
+  jrnl->last_transaction_offset = file_end;
+  fseeko(jrnl->fd, YDB_jrnl_last_transaction_offset, SEEK_SET);
+  fwrite(&file_end_le, sizeof(YDB_Offset), 1, jrnl->fd);
+
+  fsync(fileno(jrnl->fd)); // Checkpoint
+
+  if (prev != 0) {
+    fseeko(jrnl->fd, prev + YDB_jrnl_transaction_next_offset, SEEK_SET);
+  } else {
+    fseeko(jrnl->fd, YDB_jrnl_first_transaction_offset, SEEK_SET);
+  }
+  fwrite(&file_end_le, sizeof(YDB_Offset), 1, jrnl->fd);
+
+  fsync(fileno(jrnl->fd)); // Checkpoint
+
+  fseeko(jrnl->fd, file_end, SEEK_SET);
+  uint32_t op_cnt = ydb_transaction_ops_size_get(t);
+  for (uint32_t i = 0; i < op_cnt; ++i) {
+    YDB_TransactionOp* op = ydb_transaction_op_at(t, i);
+    fwrite(&op->opcode, sizeof(YDB_OpCode), 1, jrnl->fd);
+    fwrite(&op->size, sizeof(YDB_OpDataSize), 1, jrnl->fd);
+    fwrite(&op->data, op->size, 1, jrnl->fd);
+    fsync(fileno(jrnl->fd));
+  }
+  // Write completion op
+  fputc(YDB_jrnl_op_complete, jrnl->fd);
+  YDB_OpDataSize sz = 0;
+#ifndef NO_EASTER_EGGS
+  char easter[] = "Andrew is a pi-door-ass";
+  sz = sizeof(easter) - 1;
+  fwrite(&sz, sizeof(YDB_OpDataSize), 1, jrnl->fd);
+  fwrite(easter, sz, 1, jrnl->fd);
+#else
+  fwrite(&sz, sizeof(YDB_OpDataSize), 1, jrnl->fd);
+#endif
+  fsync(fileno(jrnl->fd));
+
+  return __ydb_jrnl_read(jrnl, file_end);
+}
+
+YDB_Transaction *ydb_journal_get_current_transaction(YDB_Journal *jrnl) {
+  THROW_IF_NULL(jrnl, NULL);
+  THROW_IF_NULL(jrnl->in_use, NULL);
+  THROW_IF_NULL(jrnl->is_consistent, NULL);
+  THROW_IF_NULL(jrnl->first_transaction_offset, NULL);
+
+  return jrnl->curr_transaction;
+}
+
+#ifdef __cplusplus
+}
+#endif

src/journal/transaction.c

@@ -0,0 +1,101 @@
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <YeltsinDB/types.h>
+#include <YDB_ext/vec.h>
+#include <YeltsinDB/journal/transaction_op.h>
+#include <YeltsinDB/macro.h>
+#include <YeltsinDB/error_code.h>
+#include <YeltsinDB/journal/transaction.h>
+
+typedef vec_t(YDB_TransactionOp*) vec_op_t;
+
+struct __YDB_Transaction {
+  YDB_Timestamp timestamp;
+  YDB_Flags flags;
+  vec_op_t ops;
+};
+
+YDB_Transaction *ydb_transaction_create() {
+  YDB_Transaction* result = calloc(1, sizeof(YDB_Transaction));
+  vec_init(&result->ops);
+  return result;
+}
+
+void ydb_transaction_destroy(YDB_Transaction *t) {
+  THROW_IF_NULL(t, (void)0);
+  int i; YDB_TransactionOp* op;
+  vec_foreach(&t->ops, op, i) {
+      ydb_transaction_op_destroy(t->ops.data[i]);
+  }
+  vec_deinit(&t->ops);
+  free(t);
+}
+YDB_Timestamp ydb_transaction_timestamp_get(YDB_Transaction *t) {
+  THROW_IF_NULL(t, 1 << sizeof(YDB_Timestamp)); // NOLINT minimal signed int value
+  return t->timestamp;
+}
+YDB_Error ydb_transaction_timestamp_set(YDB_Transaction *t, YDB_Timestamp timestamp) {
+  THROW_IF_NULL(t, YDB_ERR_TRANSACTION_NOT_INITIALIZED);
+  t->timestamp = timestamp;
+  return YDB_ERR_SUCCESS;
+}
+
+YDB_Flags ydb_transaction_flags_get(YDB_Transaction *t) {
+  THROW_IF_NULL(t, 0); // NOLINT minimal signed int value
+  return t->flags;
+}
+
+YDB_Error ydb_transaction_flags_set(YDB_Transaction *t, YDB_Flags flags) {
+  THROW_IF_NULL(t, YDB_ERR_TRANSACTION_NOT_INITIALIZED);
+  t->flags = flags;
+  return YDB_ERR_SUCCESS;
+}
+
+uint32_t ydb_transaction_ops_size_get(YDB_Transaction *t) {
+  THROW_IF_NULL(t, 0);
+  return t->ops.length;
+}
+
+YDB_Error ydb_transaction_push_op(YDB_Transaction* t, YDB_TransactionOp *op) {
+  THROW_IF_NULL(t, YDB_ERR_TRANSACTION_NOT_INITIALIZED);
+  YDB_TransactionOp* op_copy = ydb_transaction_op_clone(op);
+  if(vec_push(&t->ops, op_copy)) {
+    return YDB_ERR_TRANSACTION_OP_PUSH_FAILED;
+  }
+  return YDB_ERR_SUCCESS;
+}
+
+YDB_Error ydb_transaction_pop_op(YDB_Transaction *t) {
+  THROW_IF_NULL(t, YDB_ERR_TRANSACTION_NOT_INITIALIZED);
+  uint32_t vec_back = t->ops.length - 1;
+  ydb_transaction_op_destroy(t->ops.data[vec_back]);
+  vec_pop(&t->ops);
+  return YDB_ERR_SUCCESS;
+}
+
+YDB_TransactionOp *ydb_transaction_op_at(YDB_Transaction *t, uint32_t index) {
+  THROW_IF_NULL(t, NULL);
+  if (index > ydb_transaction_ops_size_get(t)) {
+    return NULL;
+  }
+  return t->ops.data[index];
+}
+
+YDB_Transaction *ydb_transaction_clone(YDB_Transaction *t) {
+  THROW_IF_NULL(t, NULL);
+  YDB_Transaction* r = ydb_transaction_create();
+  r->timestamp = t->timestamp;
+  r->flags = t->flags;
+  int i; YDB_TransactionOp* op;
+  vec_foreach(&t->ops, op, i) {
+    vec_push(&r->ops, ydb_transaction_op_clone(op));
+  }
+
+  return r;
+}
+
+#ifdef __cplusplus
+}
+#endif

src/ydb.c

@@ -11,6 +11,11 @@ extern "C" {
 #include <YeltsinDB/constants.h>
 #include <YeltsinDB/macro.h>
 #include <YeltsinDB/table_page.h>
+#ifndef NO_JOURNAL
+#include <YeltsinDB/journal.h>
+#include <YeltsinDB/journal/transaction.h>
+#include <YeltsinDB/journal/transaction_op.h>
+#endif
 #include <YeltsinDB/ydb.h>
 
 struct __YDB_Engine {
@@ -29,16 +34,27 @@ struct __YDB_Engine {
   uint8_t in_use; /**< "In use" flag. */
   char *filename; /**< Current table data file name. */
   FILE *fd; /**< Current table data file descriptor. */
+
+#ifndef NO_JOURNAL
+  YDB_Journal* jrnl;
+#endif
 };
 
 YDB_Engine *ydb_init_instance() {
   YDB_Engine *new_instance = calloc(1, sizeof(YDB_Engine));
+#ifndef NO_JOURNAL
+  new_instance->jrnl = ydb_journal_init();
+#endif
   return new_instance;
 }
 
 void ydb_terminate_instance(YDB_Engine *instance) {
   ydb_unload_table(instance);
 
+#ifndef NO_JOURNAL
+  ydb_journal_destroy(instance->jrnl);
+#endif
+
   // And after all that, the instance could be freed
   free(instance);
 }
@@ -91,6 +107,14 @@ static YDB_Error __ydb_read_page(YDB_Engine *inst) {
 // Moves file position to allocated block.
 // Also changes last_free_page_offset.
 static YDB_Offset __ydb_allocate_page_and_seek(YDB_Engine *inst) {
+  // TODO journal
+#ifndef NO_JOURNAL
+  YDB_Transaction* t = ydb_transaction_create();
+  YDB_TransactionOp* op_alloc = malloc(sizeof(YDB_TransactionOp));
+  op_alloc->opcode = YDB_jrnl_op_page_alloc;
+  op_alloc->size = 24;
+  op_alloc->data = malloc(op_alloc->size);
+#endif
   // TODO change signature of the function. It should return an error code, I think.
   YDB_Offset result = 0;
   // If no free pages in the table, then...
@@ -118,7 +142,7 @@ static YDB_Offset __ydb_allocate_page_and_seek(YDB_Engine *inst) {
     inst->last_page_offset = result;
     fseek(inst->fd, YDB_v1_last_page_offset, SEEK_SET);
     fwrite(&allocated_page_offset_le, sizeof(YDB_Offset), 1, inst->fd);
-    fflush(inst->fd);
+    fsync(fileno(inst->fd));
   } else {
     // Return last free page offset
     result = inst->last_free_page_offset;
@@ -143,7 +167,7 @@ static YDB_Offset __ydb_allocate_page_and_seek(YDB_Engine *inst) {
     YDB_Offset lfp_offset_le = TO_LE(inst->last_free_page_offset);
     fwrite(&lfp_offset_le, sizeof(YDB_Offset), 1, inst->fd);
   }
-  fflush(inst->fd);
+  fsync(fileno(inst->fd));
   fseek(inst->fd, result, SEEK_SET);
   return result;
 }
@@ -303,7 +327,7 @@ YDB_Error ydb_append_page(YDB_Engine* instance, YDB_TablePage* page) {
   fwrite(&rc_le, sizeof(rc), 1, instance->fd);
   fwrite(d, sizeof(d), 1, instance->fd);
 
-  fflush(instance->fd);
+  fsync(fileno(instance->fd));
 
   __ydb_read_page(instance);
 
@@ -343,7 +367,7 @@ YDB_Error ydb_replace_current_page(YDB_Engine *instance, YDB_TablePage *page) {
   fwrite(page_data, sizeof(page_data), 1, instance->fd);
 
   // Flush buffer
-  fflush(instance->fd);
+  fsync(fileno(instance->fd));
 
   ydb_page_free(instance->curr_page);
   instance->curr_page = page;
@@ -398,7 +422,7 @@ YDB_Error ydb_delete_current_page(YDB_Engine *instance) {
   fwrite(&cp_le, sizeof(YDB_Offset), 1, instance->fd);
 
   // Flush buffer
-  fflush(instance->fd);
+  fsync(fileno(instance->fd));
 
   // Seek to the next page if it's not the last, else seek to the previous one
   if (instance->next_page_offset != 0) {
@@ -431,6 +455,10 @@ YDB_Error ydb_seek_to_end(YDB_Engine *instance) {
   return __ydb_read_page(instance);
 }
 
+YDB_Error ydb_commit_changes(YDB_Engine *instance) {
+  return 0;
+}
+
 #ifdef __cplusplus
 }
 #endif