** CHANGES ARE EXPERIMENTAL (FOR TESTING ONLY)

Bockchain:
1. Optim: Multi-thread long-hash computation when encountering groups of blocks.
2. Optim: Cache verified txs and return result from cache instead of re-checking whenever possible.
3. Optim: Preload output-keys when encoutering groups of blocks. Sort by amount and global-index before bulk querying database and multi-thread when possible.
4. Optim: Disable double spend check on block verification, double spend is already detected when trying to add blocks.
5. Optim: Multi-thread signature computation whenever possible.
6. Patch: Disable locking (recursive mutex) on called functions from check_tx_inputs which causes slowdowns (only seems to happen on ubuntu/VMs??? Reason: TBD)
7. Optim: Removed looped full-tx hash computation when retrieving transactions from pool (???).
8. Optim: Cache difficulty/timestamps (735 blocks) for next-difficulty calculations so that only 2 db reads per new block is needed when a new block arrives (instead of 1470 reads).

Berkeley-DB:
1. Fix: 32-bit data errors causing wrong output global indices and failure to send blocks to peers (etc).
2. Fix: Unable to pop blocks on reorganize due to transaction errors.
3. Patch: Large number of transaction aborts when running multi-threaded bulk queries.
4. Patch: Insufficient locks error when running full sync.
5. Patch: Incorrect db stats when returning from an immediate exit from "pop block" operation.
6. Optim: Add bulk queries to get output global indices.
7. Optim: Modified output_keys table to store public_key+unlock_time+height for single transaction lookup (vs 3)
8. Optim: Used output_keys table retrieve public_keys instead of going through output_amounts->output_txs+output_indices->txs->output:public_key
9. Optim: Added thread-safe buffers used when multi-threading bulk queries.
10. Optim: Added support for nosync/write_nosync options for improved performance (*see --db-sync-mode option for details)
11. Mod: Added checkpoint thread and auto-remove-logs option.
12. *Now usable on 32-bit systems like RPI2.

LMDB:
1. Optim: Added custom comparison for 256-bit key tables (minor speed-up, TBD: get actual effect)
2. Optim: Modified output_keys table to store public_key+unlock_time+height for single transaction lookup (vs 3)
3. Optim: Used output_keys table retrieve public_keys instead of going through output_amounts->output_txs+output_indices->txs->output:public_key
4. Optim: Added support for sync/writemap options for improved performance (*see --db-sync-mode option for details)
5. Mod: Auto resize to +1GB instead of multiplier x1.5

ETC:
1. Minor optimizations for slow-hash for ARM (RPI2). Incomplete.
2. Fix: 32-bit saturation bug when computing next difficulty on large blocks.

[PENDING ISSUES]
1. Berkely db has a very slow "pop-block" operation. This is very noticeable on the RPI2 as it sometimes takes > 10 MINUTES to pop a block during reorganization.
   This does not happen very often however, most reorgs seem to take a few seconds but it possibly depends on the number of outputs present. TBD.
2. Berkeley db, possible bug "unable to allocate memory". TBD.

[NEW OPTIONS] (*Currently all enabled for testing purposes)
1. --fast-block-sync arg=[0:1] (default: 1)
	a. 0 = Compute long hash per block (may take a while depending on CPU)
	b. 1 = Skip long-hash and verify blocks based on embedded known good block hashes (faster, minimal CPU dependence)
2. --db-sync-mode arg=[[safe|fast|fastest]:[sync|async]:[nblocks_per_sync]] (default: fastest:async:1000)
	a. safe = fdatasync/fsync (or equivalent) per stored block. Very slow, but safest option to protect against power-out/crash conditions.
	b. fast/fastest = Enables asynchronous fdatasync/fsync (or equivalent). Useful for battery operated devices or STABLE systems with UPS and/or systems with battery backed write cache/solid state cache.
	Fast    - Write meta-data but defer data flush.
	Fastest - Defer meta-data and data flush.
	Sync    - Flush data after nblocks_per_sync and wait.
	Async   - Flush data after nblocks_per_sync but do not wait for the operation to finish.
3. --prep-blocks-threads arg=[n] (default: 4 or system max threads, whichever is lower)
        Max number of threads to use when computing long-hash in groups.
4. --show-time-stats arg=[0:1] (default: 1)
	Show benchmark related time stats.
5. --db-auto-remove-logs arg=[0:1] (default: 1)
	For berkeley-db only. Auto remove logs if enabled.

**Note: lmdb and berkeley-db have changes to the tables and are not compatible with official git head version.
	At the moment, you need a full resync to use this optimized version.

[PERFORMANCE COMPARISON]
**Some figures are approximations only.
Using a baseline machine of an i7-2600K+SSD+(with full pow computation):
1. The optimized lmdb/blockhain core can process blocks up to 585K for ~1.25 hours + download time, so it usually takes 2.5 hours to sync the full chain.
2. The current head with memory can process blocks up to 585K for ~4.2 hours + download time, so it usually takes 5.5 hours to sync the full chain.
3. The current head with lmdb can process blocks up to 585K for ~32 hours + download time and usually takes 36 hours to sync the full chain.

Averate procesing times (with full pow computation):
lmdb-optimized:
1. tx_ave = 2.5 ms / tx
2. block_ave = 5.87 ms / block
memory-official-repo:
1. tx_ave = 8.85 ms / tx
2. block_ave = 19.68 ms / block
lmdb-official-repo (0f4a036437fd41a5498ee5e74e2422ea6177aa3e)
1. tx_ave = 47.8 ms / tx
2. block_ave = 64.2 ms / block

**Note: The following data denotes processing times only (does not include p2p download time)
lmdb-optimized processing times (with full pow computation):
1. Desktop,  Quad-core / 8-threads 2600k  (8Mb) - 1.25 hours processing time (--db-sync-mode=fastest:async:1000).
2. Laptop,   Dual-core / 4-threads U4200  (3Mb) - 4.90 hours processing time (--db-sync-mode=fastest:async:1000).
3. Embedded, Quad-core / 4-threads Z3735F (2x1Mb) - 12.0 hours processing time (--db-sync-mode=fastest:async:1000).

lmdb-optimized processing times (with per-block-checkpoint)
1. Desktop,  Quad-core / 8-threads 2600k  (8Mb) - 10 minutes processing time (--db-sync-mode=fastest:async:1000).

berkeley-db optimized processing times (with full pow computation)
1. Desktop, Quad-core / 8-threads 2600k  (8Mb) - 1.8 hours processing time (--db-sync-mode=fastest:async:1000).
2. RPI2. Improved from estimated 3 months(???) into 2.5 days (*Need 2AMP supply + Clock:1Ghz + [usb+ssd] to achieve this speed) (--db-sync-mode=fastest:async:1000).

berkeley-db optimized processing times (with per-block-checkpoint)
1. RPI2. 12-15 hours (*Need 2AMP supply + Clock:1Ghz + [usb+ssd] to achieve this speed) (--db-sync-mode=fastest:async:1000).

1 files changed, 69 insertions, 7 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b52ea8f41..9ec6d2c3a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -45,6 +45,35 @@ function (die msg)
   message(FATAL_ERROR "${BoldRed}${msg}${ColourReset}")
 endfunction ()
 
+if (NOT ${ARCH} STREQUAL "")
+	string(SUBSTRING ${ARCH} 0 5 ARM_TEST)
+	string(TOLOWER ${ARM_TEST} ARM_TEST)
+	
+	if (${ARM_TEST} STREQUAL "armv6")
+		set(ARM6 1)
+	else()
+		set(ARM6 0)
+	endif()
+	   
+	if (${ARM_TEST} STREQUAL "armv7")
+		set(ARM7 1)
+	else()
+		set(ARM7 0)
+	endif()	
+endif()
+
+if(WIN32 OR ARM7 OR ARM6)
+	set(CMAKE_C_FLAGS_RELEASE "-O2 -DNDEBUG")
+	set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG")
+endif()
+
+# set this to 0 if per-block checkpoint needs to be disabled
+set(PER_BLOCK_CHECKPOINT 1)
+
+if(PER_BLOCK_CHECKPOINT)
+  add_definitions("-DPER_BLOCK_CHECKPOINT")
+endif()
+
 list(INSERT CMAKE_MODULE_PATH 0
   "${CMAKE_SOURCE_DIR}/cmake")
 
@@ -156,14 +185,42 @@ if (DEFINED ENV{DATABASE})
 else()
   message(STATUS "Could not find DATABASE in env (not required unless you want to change database type from default: ${DATABASE})")
 endif()
+
+set(BERKELEY_DB 0)
 if (DATABASE STREQUAL "lmdb")
   set(BLOCKCHAIN_DB DB_LMDB)
+  
+  # temporarily allow mingw to compile with berkeley_db,
+  # regardless if building static or not
+  if(NOT STATIC OR MINGW)
+	  find_package(BerkeleyDB)
+		
+	  if(NOT BERKELEY_DB_LIBRARIES)
+	    message(STATUS "BerkeleyDB not found and has been disabled.")
+	  else()
+	    message(STATUS "Found BerkeleyDB include (db.h) in ${BERKELEY_DB_INCLUDE_DIR}")
+		if(BERKELEY_DB_LIBRARIES)
+		  message(STATUS "Found BerkeleyDB shared library")
+		  set(BDB_STATIC false CACHE BOOL "BDB Static flag")
+		  set(BDB_INCLUDE ${BERKELEY_DB_INCLUDE_DIR} CACHE STRING "BDB include path")
+		  set(BDB_LIBRARY ${BERKELEY_DB_LIBRARIES} CACHE STRING "BDB library name")
+		  set(BDB_LIBRARY_DIRS "" CACHE STRING "BDB Library dirs")
+		  set(BERKELEY_DB 1)
+		else()
+		  message(STATUS "Found BerkeleyDB includes, but could not find BerkeleyDB library. Please make sure you have installed libdb and libdb-dev or the equivalent")
+		endif()
+	  endif()
+  endif()
 elseif (DATABASE STREQUAL "memory")
   set(BLOCKCHAIN_DB DB_MEMORY)
 else()
   die("Invalid database type: ${DATABASE}")
 endif()
 
+if(BERKELEY_DB)
+  add_definitions("-DBERKELEY_DB")
+endif()
+	
 add_definitions("-DBLOCKCHAIN_DB=${BLOCKCHAIN_DB}")
 
 if (UNIX AND NOT APPLE)
@@ -192,7 +249,7 @@ include_directories(external/rapidjson)
 include_directories(${LMDB_INCLUDE})
 
 # Final setup for Berkeley DB
-if (NOT STATIC)
+if (BERKELEY_DB)
   include_directories(${BDB_INCLUDE})
 endif()
 
@@ -208,13 +265,14 @@ if(MSVC)
   include_directories(SYSTEM src/platform/msc)
 else()
   set(ARCH native CACHE STRING "CPU to build for: -march value or default")
-  if(ARCH STREQUAL "default")
+  # -march=armv7-a conflicts with -mcpu=cortex-a7
+  if(ARCH STREQUAL "default" OR ARM7)
     set(ARCH_FLAG "")
   else()
     if(ARCH STREQUAL "x86_64")
       set(ARCH_FLAG "-march=x86-64")
     else()
-      set(ARCH_FLAG "-march=${ARCH}")
+       set(ARCH_FLAG "-march=${ARCH}")
     endif()
   endif()
   set(WARNINGS "-Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Wno-error=extra -Wno-error=deprecated-declarations -Wno-error=sign-compare -Wno-error=strict-aliasing -Wno-error=type-limits -Wno-unused-parameter -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized")
@@ -258,14 +316,18 @@ else()
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -D_GNU_SOURCE ${MINGW_FLAG} ${WARNINGS} ${CXX_WARNINGS} ${ARCH_FLAG} -maes")
   endif()
 
-  string(SUBSTRING ${ARCH} 0 3 ARM_TEST)
-  string(TOLOWER ${ARM_TEST} ARM_TEST)
-  if(${ARM_TEST} STREQUAL "arm")
-    message(STATUS "Setting ARM C and C++ flags")
+  if(ARM6)
+    message(STATUS "Setting ARM6 C and C++ flags")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mfpu=vfp -mfloat-abi=hard")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mfpu=vfp -mfloat-abi=hard")
   endif()
 
+  if(ARM7)
+    message(STATUS "Setting ARM7 C and C++ flags")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O2 -mcpu=cortex-a7 -mfloat-abi=hard -mfpu=vfpv4 -funsafe-math-optimizations -mtune=cortex-a7")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2 -mcpu=cortex-a7 -mfloat-abi=hard -mfpu=vfpv4 -funsafe-math-optimizations -mtune=cortex-a7")
+  endif()
+
   if(APPLE)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DGTEST_HAS_TR1_TUPLE=0")
   endif()