Alexander Naumchuk - «GC time garbage collection» (Ideeli)

1. GC
NO effort CLEAN memory

2. GC
NO effort CLEAN memory
SOME

3. Who am I?
Alex Naumchuk
Software Architect at
Consulter at Brightgrove
alex.naumchuk@gmail.com

4. What IS GC?

5. What IS GC?
Developers

6. 80k req/min 10k db queries/sec 125 prod servers
avg response time: 25ms

7. Automatic collector reclaiming garbage
C, C++

8. Automatic collector reclaiming garbage
C, C++
Ruby, Java, .NET

9. Automatic collector reclaiming garbage
C, C++ ALLY
MA NU
D o it
Ruby, Java, .NET

10. Automatic collector reclaiming garbage
C, C++ ALLY
MA NU
D o it
Ruby, Java, .NET about it
’t C ARE
Don

11. Should you care about memory?

12. Should you care about memory?
YES!

13. Should you care about memory?
YES!
at least know how it works

14. REE/MRI Memory organization
Heaps
slot slot slot slot slot
slot slot slot slot slot
slot slot slot slot slot

15. Slot RVALUE
typedef struct RVALUE {
union {
struct {
unsigned long flags; /* always 0 for freed obj */
struct RVALUE *next;
} free;
struct RBasic basic;
struct RObject object;
struct RClass klass;
struct RFloat flonum;
struct RString string;
struct RArray array;
struct RRegexp regexp;
struct RHash hash;
struct RData data;
struct RStruct rstruct;
struct RBignum bignum;
struct RFile file;
struct RNode node;
struct RMatch match;
struct RVarmap varmap;
struct SCOPE scope;
} as;
} RVALUE;

16. REE GC Options

17. Default Settings
RUBY_HEAP_SLOTS 10000

18. Default Settings
RUBY_HEAP_SLOTS 10000
RUBY_HEAP_SLOTS_INCREMENT 10000

19. Default Settings
RUBY_HEAP_SLOTS 10000
RUBY_HEAP_SLOTS_INCREMENT 10000
RUBY_HEAP_SLOTS_GROWTH_FACTOR 1.8

20. Default Settings
RUBY_HEAP_SLOTS 10000
RUBY_HEAP_SLOTS_INCREMENT 10000
RUBY_HEAP_SLOTS_GROWTH_FACTOR 1.8
RUBY_GC_MALLOC_LIMIT 8000000

21. Default Settings
RUBY_HEAP_SLOTS 10000
RUBY_HEAP_SLOTS_INCREMENT 10000
RUBY_HEAP_SLOTS_GROWTH_FACTOR 1.8
RUBY_GC_MALLOC_LIMIT 8000000
RUBY_HEAP_FREE_MIN 4096

22. Ideeli Settings
MM FE
RUBY_HEAP_SLOTS 6000000 2400000
RUBY_HEAP_SLOTS_INCREMENT 100000 100000
RUBY_HEAP_SLOTS_GROWTH_FACTOR 1 1
RUBY_GC_MALLOC_LIMIT 100000000 40000000
RUBY_HEAP_FREE_MIN 3500000 100000

23. When GC runs
malloc limit exceeded
min free slots < free slots
not enough slots to allocate value

24. Mark Phase

25. GC Flow
Mark
Sweep
Finalize

26. Statistics
>>ObjectSpace.statistics
Number of objects : 1631452 (1291302 AST nodes, 79.15%)
Heap slot size : 40
GC cycles so far : 32
Number of heaps : 9
Total size of objects : 63728.59 KB
Total size of heaps : 119579.81 KB (55851.22 KB = 46.71% unused)
Leading free slots : 1154340 (45091.41 KB = 37.71%)
Trailing free slots : 4 (0.16 KB = 0.00%)
Number of contiguous groups of 16 slots: 76771 (40.13%)
Number of terminal objects: 8973 (0.29%)

27. Other Stats
GC.enable_stats
GC.disable_stats
GC.collections
GC.time
GC.growth
GC.clear_stats
GC.dump
GC.allocated_size
GC.num_allocations
ObjectSpace.live_objects
ObjectSpace.allocated_objects

28. Let’s Play
Let’s play

29. Code
GC.enable_stats
require ‘config/environment’
GC.time
GC.num_allocations
GC.collections

30. Default options
GC.enable_stats
require ‘config/environment’
GC.time ~2 Seconds
GC.num_allocations 5_635_070
GC.collections 31

31. ObjectSpace.statistics
Number of objects : 1643029 (1265158 AST nodes, 77.00%)
Heap slot size : 40
GC cycles so far : 31
Number of heaps : 9
Total size of objects : 64180.82 KB
Total size of heaps : 119579.42 KB (55398.60 KB = 46.33% unused)
Leading free slots : 1093423 (42711.84 KB = 35.72%)
Trailing free slots : 0 (0.00 KB = 0.00%)
Number of contiguous groups of 16 slots: 73754 (38.55%)
Number of terminal objects: 7274 (0.24%)

32. Default options
• Too many GC cycles
• Many heaps
• Bad heap utilization

33. New options
RUBY_HEAP_MIN_SLOTS = 1_800_000
RUBY_GC_MALLOC_LIMIT = 50_000_000
GC.time ~1 Second
GC.num_allocations 5_634_856
GC.collections 6

34. New options
RUBY_HEAP_MIN_SLOTS = 1_800_000
RUBY_GC_MALLOC_LIMIT = 50_000_000
Number of objects : 1682325 (1272351 AST nodes, 75.63%)
Heap slot size : 40
GC cycles so far :6
Number of heaps : 1
Total size of objects : 65715.82 KB
Total size of heaps : 70312.51 KB (4596.69 KB = 6.54% unused)
Leading free slots : 39246 (1533.05 KB = 2.18%)
Trailing free slots : 0 (0.00 KB = 0.00%)
Number of contiguous groups of 16 slots: 4305 (3.83%)
Number of terminal objects: 7435 (0.41%)

35. Can we do it even better?

36. Can we do it even better?
YES!

37. Enhanced options
RUBY_HEAP_MIN_SLOTS = 2_100_000
RUBY_GC_MALLOC_LIMIT = 100_000_000
GC.time ~0.8 Second
GC.num_allocations 5_634_892
GC.collections 3

38. Enhanced options
RUBY_HEAP_MIN_SLOTS = 2_100_000
RUBY_GC_MALLOC_LIMIT = 100_000_000
Number of objects : 1816515 (1297270 AST nodes, 71.42%)
Heap slot size : 40
GC cycles so far :3
Number of heaps : 1
Total size of objects : 70957.62 KB
Total size of heaps : 82031.26 KB (11073.64 KB = 13.50% unused)
Leading free slots : 0 (0.00 KB = 0.00%)
Trailing free slots : 0 (0.00 KB = 0.00%)
Number of contiguous groups of 16 slots: 5807 (4.42%)
Number of terminal objects: 7969 (0.38%)

39. What about memory?
Before 325.9M
After 347.2M
21.3M

40. Garbage Recon

41. Garbage Recon
AVG GC AVG Object AVG Req
Action
Rounds Allocations between GC
/cart_items/index 0.61 330651 2
/cart_items/ID/ 1.21 651679 1
/cart_items 0.93 498881 1
/store/confirm_reservation_address 0.15 76084 6
/store/confirm_reservation 1.37 724095 1

42. In between request GC
User Request
Response
GC

43. It’s a trap

44. The Code
class Test
attr_accessor :i_val
def initialize
@i_val = []
300_000.times do |i|
@i_val << "ruby-#{i}" * 10
end
end
def say_hello
"hello"
end
end

45. The Test
test = Test.new
GC.start
t.i_val = nil
t.say_hello
GC.start
t = []
GC.start

46. Results
test = Test.new # 1504032
t.i_val = nil # 3922
t = [] # 3916

47. Conclusion
• be careful with the big sets of data
• don’t store big amount of data in object with long life time
• even if current request wont spend much time in GC the
next request would do it
• the more objects - the longer is mark phase
• symbols are not collected but increase mark phase time

48. Questions?