diff --git a/src/db/idb.c b/src/db/idb.c
new file mode 100644
index 0000000..7cf03dd
--- /dev/null
+++ b/src/db/idb.c
@@ -0,0 +1,252 @@
+#include "idb.h"
+#include "tlibc/filesystem.h"
+
+static const Magic32 TABLE_FILE_MAGIC = { .bytes = { 'I', 'D', 'B', 't' } };
+#define IDB_VERSION 0x01
+
+Result(void) Table_setDirtyBit(Table* t, bool val);
+Result(bool) Table_getDirtyBit(Table* t);
+
+void Table_close(Table* t){
+    fclose(t->table_file);
+    fclose(t->changes_file);
+    free(t->name.data);
+    free(t->table_file_path.data);
+    free(t->changes_file_path.data);
+    free(t);
+}
+
+void TablePtr_destroy(void* t_ptr_ptr){
+    Table_close(*(Table**)t_ptr_ptr);
+}
+
+/// @param name must be null-terminated
+Result(void) validateTableName(str name){
+    char forbidden_characters[] = { '/', '\\', ':', ';', '?', '"', '\'', '\n', '\r', '\t'};
+    for(u32 i = 0; i < ARRAY_LEN(forbidden_characters); i++) {
+        char c = forbidden_characters[i];
+        if(str_seekChar(name, c, 0) != -1){
+            return RESULT_ERROR_FMT(
+                "Table name '%s' contains forbidden character '%c'",
+                name.data, c);
+        }
+    }
+    
+    return RESULT_VOID;
+}
+
+Result(void) Table_readHeader(Table* t){
+    // seek for start of the file
+    try_void(file_seek(t->table_file, 0, SeekOrigin_Start), )
+    // read header
+    try_void(file_readStructsExactly(t->table_file, &t->header, sizeof(t->header), 1), );
+    return RESULT_VOID;
+}
+
+Result(void) Table_writeHeader(Table* t){
+    // seek for start of the file
+    try_void(file_seek(t->table_file, 0, SeekOrigin_Start), )
+    // write header
+    try_void(file_writeStructs(t->table_file, &t->header, sizeof(t->header), 1), );
+    return RESULT_VOID;
+}
+
+Result(void) Table_setDirtyBit(Table* t, bool val){
+    t->header._dirty_bit = val;
+    try_void(Table_writeHeader(t), );
+    return RESULT_VOID;
+}
+
+Result(bool) Table_getDirtyBit(Table* t){
+    try_void(Table_readHeader(t), );
+    return RESULT_VALUE(i, t->header._dirty_bit);
+}
+
+Result(void) Table_calculateRowCount(Table* t){
+    try(file_size, file_getSize(t->table_file), );
+    i64 data_size = file_size.i - sizeof(t->header);
+    if(data_size % t->header.row_size != 0){
+        //TODO: fix table instead of trowing error
+        return RESULT_ERROR_FMT(
+            "Table '%s' has invalid size. Last row is incomplete", 
+            t->name.data);
+    }
+
+    t->row_count = data_size / t->header.row_size;
+    return RESULT_VOID;
+}
+
+Result(void) Table_validateHeader(Table* t){
+    if(t->header.magic.n != TABLE_FILE_MAGIC.n
+            || t->header.row_size == 0)
+    {
+        return RESULT_ERROR_FMT(
+            "Table file '%s' has invalid header", 
+            t->table_file_path.data);
+    }
+    
+    //TODO: check version
+    
+    try(dirty_bit, Table_getDirtyBit(t), );
+    if(dirty_bit.i){
+        //TODO: handle dirty bit instead of throwing error
+        return RESULT_ERROR_FMT(
+            "Table file '%s' has dirty bit set", 
+            t->table_file_path.data);
+    }
+
+    return RESULT_VOID;
+}
+
+Result(void) Table_validateRowSize(Table* t, u32 row_size){
+    if(row_size != t->header.row_size){
+        Result(void) error_result = RESULT_ERROR_FMT(
+            "Requested row size (%u) doesn't match saved row size (%u)",
+            row_size, t->header.row_size);
+        return error_result;
+    }
+
+    return RESULT_VOID;
+}
+
+Result(IncrementalDB*) idb_open(str db_dir){
+    IncrementalDB* db = (IncrementalDB*)malloc(sizeof(IncrementalDB));
+    // value of *db must be set to zero or behavior of idb_close will be undefined
+    memset(db, 0, sizeof(IncrementalDB));
+    db->db_dir = str_copy(db_dir);
+    try_void(dir_create(db->db_dir.data), 
+        idb_close(db));
+    HashMap_construct(&db->tables_map, Table*, TablePtr_destroy);
+    return RESULT_VALUE(p, db);
+}
+
+void idb_close(IncrementalDB* db){
+    free(db->db_dir.data);
+    HashMap_destroy(&db->tables_map);
+    free(db);
+}
+
+Result(Table*) idb_getOrCreateTable(IncrementalDB* db, str _table_name, u32 row_size){
+    // TODO: implement whole db lock
+
+    Table** tpp = HashMap_tryGetPtr(&db->tables_map, _table_name);
+    if(tpp != NULL){
+        Table* existing_table = *tpp;
+        try_void(Table_validateRowSize(existing_table, row_size), );
+        return RESULT_VALUE(p, existing_table);
+    }
+
+    str table_name_null_terminated = str_copy(_table_name);
+    try_void(validateTableName(table_name_null_terminated), 
+        free(table_name_null_terminated.data));
+
+    Table* t = (Table*)malloc(sizeof(Table));
+    // value of *t must be set to zero or behavior of Table_close will be undefined
+    memset(t, 0, sizeof(Table));
+    
+    t->db = db;
+    t->name = table_name_null_terminated;
+    t->table_file_path = str_from_cstr(
+        strcat_malloc(db->db_dir.data, path_seps, t->name.data, ".table.idb"));
+    t->changes_file_path = str_from_cstr(
+        strcat_malloc(db->db_dir.data, path_seps, t->name.data, ".changes.idb"));
+
+    bool table_exists = file_exists(t->table_file_path.data);
+
+    // open or create file with table data
+    try(_table_file, file_openOrCreateReadWrite(t->table_file_path.data), 
+        Table_close(t));
+    t->table_file = _table_file.p;
+
+    // open or create file with backups of updated rows
+    try(_changes_file, file_openOrCreateReadWrite(t->changes_file_path.data), 
+        Table_close(t));
+    t->changes_file = _changes_file.p;
+
+    if(table_exists){
+        try_void(Table_readHeader(t), 
+            Table_close(t));
+        try_void(Table_validateHeader(t), 
+            Table_close(t));
+        try_void(Table_validateRowSize(t, row_size),
+            Table_close(t));
+        try_void(Table_calculateRowCount(t), 
+            Table_close(t));
+    }
+    else {
+        t->header.magic.n = TABLE_FILE_MAGIC.n;
+        t->header.row_size = row_size;
+        t->header.version = IDB_VERSION;
+        try_void(Table_writeHeader(t), 
+            Table_close(t));
+    }
+
+    if(!HashMap_tryPush(&db->tables_map, t->name, &t)){
+        Result(void) error_result = RESULT_ERROR_FMT(
+            "Table '%s' is already open", 
+            t->name.data);
+        Table_close(t);
+        return error_result;
+    }
+
+    return RESULT_VALUE(p, t);
+}
+
+Result(void) idb_getRows(Table* t, u64 id, void* dst, u64 count){
+    // TODO: implement table lock
+    if(id + count > t->row_count){
+        return RESULT_ERROR_FMT(
+            "Can't read " IFWIN("%llu", "%lu") " rows at index " IFWIN("%llu", "%lu")
+            " because table '%s' has only " IFWIN("%llu", "%lu") " rows",
+            count, id, t->name.data, t->row_count);
+    }
+
+    i64 file_pos = sizeof(t->header) + id * t->header.row_size;
+
+    // seek for the row position in file
+    try_void(file_seek(t->table_file, file_pos, SeekOrigin_Start), );
+    // read rows from file
+    try_void(file_readStructsExactly(t->table_file, dst, t->header.row_size, count), );
+
+    return RESULT_VOID;
+}
+
+Result(void) idb_updateRows(Table* t, u64 id, const void* src, u64 count){
+    if(id + count >= t->row_count){
+        return RESULT_ERROR_FMT(
+            "Can't update " IFWIN("%llu", "%lu") " rows at index " IFWIN("%llu", "%lu")
+            " because table '%s' has only " IFWIN("%llu", "%lu") " rows",
+            count, id, t->name.data, t->row_count);
+    }
+
+    try_void(Table_setDirtyBit(t, true), );
+
+    i64 file_pos = sizeof(t->header) + id * t->header.row_size;
+
+    // TODO: set dirty bit in backup file too
+    // TODO: save old values to the backup file 
+    
+    // seek for the row position in file
+    try_void(file_seek(t->table_file, file_pos, SeekOrigin_Start), );
+    // replace rows in file
+    try_void(file_writeStructs(t->table_file, src, t->header.row_size, count), );
+    
+    try_void(Table_setDirtyBit(t, false), );
+    return RESULT_VOID;
+}
+
+Result(u64) idb_pushRows(Table* t, const void* src, u64 count){
+    try_void(Table_setDirtyBit(t, true), );
+
+    const u64 new_row_index = t->row_count;
+
+    // seek for end of the file
+    try_void(file_seek(t->table_file, 0, SeekOrigin_End), );
+    // write new rows to the file
+    try_void(file_writeStructs(t->table_file, src, t->header.row_size, count), );
+
+    t->row_count += count;
+
+    try_void(Table_setDirtyBit(t, false), );
+    return RESULT_VALUE(u, new_row_index);
+}
diff --git a/src/db/idb.h b/src/db/idb.h
new file mode 100644
index 0000000..d6ff62d
--- /dev/null
+++ b/src/db/idb.h
@@ -0,0 +1,50 @@
+#pragma once
+
+#include "tlibc/errors.h"
+#include "tlibc/string/str.h"
+#include "tlibc/collections/Array.h"
+#include "tlibc/collections/HashMap.h"
+
+typedef struct IncrementalDB IncrementalDB;
+
+typedef union Magic32 {
+    u32 n;
+    u8 bytes[4];
+} Magic32;
+
+typedef struct TableHeader {
+    Magic32 magic;
+    u16 version;
+    bool _dirty_bit;
+    u32 row_size;
+} __attribute__((aligned(256))) TableHeader;
+
+typedef struct Table {
+    TableHeader header;
+    IncrementalDB* db;
+    str name;
+    str table_file_path;
+    str changes_file_path;
+    FILE* table_file;
+    FILE* changes_file;
+    u64 row_count;
+} Table;
+
+typedef struct IncrementalDB {
+    str db_dir;
+    HashMap(Table**) tables_map;
+} IncrementalDB;
+
+Result(IncrementalDB*) idb_open(str db_dir);
+void idb_close(IncrementalDB* db);
+
+Result(Table*) idb_getOrCreateTable(IncrementalDB* db, str _table_name, u32 row_size);
+
+Result(void) idb_getRows(Table* t, u64 id, void* dst, u64 count);
+#define idb_getRow(T, ID, DST) idb_getRows(T, ID, DST, 1)
+
+Result(u64) idb_pushRows(Table* t, const void* src, u64 count);
+#define idb_pushRow(T, SRC) idb_pushRows(T, SRC, 1)
+
+Result(void) idb_updateRows(Table* t, u64 id, const void* src, u64 count);
+#define idb_updateRow(T, ID, SRC) idb_updateRows(T, ID, SRC, 1)
diff --git a/src/main.c b/src/main.c
index 6989fcb..aee66d3 100755
--- a/src/main.c
+++ b/src/main.c
@@ -2,8 +2,8 @@
 #include "network/network.h"
 #include "network/socket.h"
 #include "tlibc/time.h"
+#include "db/idb.h"
 #include <pthread.h>
-#include <errno.h>
 #include <assert.h>
 
 Result(void) test_aes(){
@@ -155,10 +155,41 @@ Result(void) test_network(){
     return RESULT_VOID;
 }
 
+Result(void) test_db(){
+    try(_db, idb_open(STR("idb")), );
+    IncrementalDB* db = _db.p;
+
+    const u32 row_size = 8;
+    const u32 rows_count = 5;
+    const char const_rows[5][8] = {
+        "0123456", "bebra", "abobus", "q", "DIMOOON"
+    };
+    char buffer[512];
+    memset(buffer, 0, 512);
+
+    try(_t0, idb_getOrCreateTable(db, STR("test0"), row_size), idb_close(db));
+    Table* t0 = _t0.p;
+    printf("table '%s' created\n", t0->name.data);
+    printf("\t%s\n", t0->table_file_path.data);
+    printf("\t%s\n", t0->changes_file_path.data);
+
+    idb_pushRows(t0, const_rows, rows_count);
+    
+    const u32 indices[] = { 0, 1, 4, 3, 4, 0 };
+    for(u32 i = 0; i < ARRAY_LEN(indices); i++){
+        try_void(idb_getRow(t0, indices[i], buffer), idb_close(db));
+        printf("row %u: %s\n", indices[i], buffer);
+    }
+
+    idb_close(db);
+    return RESULT_VOID;
+}
+
 int main(){
     try_fatal(_10, network_init(), );
-    try_fatal(_20, test_aes(), );
+    // try_fatal(_20, test_aes(), );
     // try_fatal(_30, test_network(), );
+    try_fatal(_40, test_db(), );
     try_fatal(_100, network_deinit(), );
     return 0;
 }