Submodule box.slab¶
The box.slab
submodule provides access to slab allocator statistics. The
slab allocator is the main allocator used to store tuples. This can be used
to monitor the total memory usage and memory fragmentation.
-
box.runtime.
info
()¶ Show a memory usage report (in bytes) for the Lua runtime.
Return: lua
is the heap size of the Lua garbage collector;maxalloc
is the maximal memory quota that can be allocated for Lua;used
is the current memory size used by Lua.
Rtype: table
Example:
tarantool> box.runtime.info() --- - lua: 913710 maxalloc: 4398046510080 used: 12582912 ... tarantool> box.runtime.info().used --- - used: 12582912 ...
-
box.slab.
info
()¶ Show an aggregated memory usage report (in bytes) for the slab allocator.
This report is useful for assessing out-of-memory risks: the risks are high if both
arena_used_ratio
andquota_used_ratio
are high (90-95%).If
quota_used_ratio
is low, then higharena_used_ratio
and/oritems_used_ratio
indicate that the memory fragmentation is low (i.e. the memory is used efficiently).If
quota_used_ratio
is high (approaching 100%), then lowarena_used_ratio
(50-60%) indicates that the memory is heavily fragmentized. Most probably, there is no immediate out-of-memory risk in this case, but generally this is an issue to consider. For example, probable risks are that the entire memory quota is used for tuples, and there is are no slabs left for a piece of an index. Or that all slabs are allocated for storing tuples, but in fact all the slabs are half-empty.Return: items_used_ratio
=items_used
/slab_count
*slab_size
(these are slabs used only for tuples, no indexes);quota_size
is the maximum amount of memory that the slab allocator can use for both tuples and indexes (as configured in slab_alloc_arena parameter, e.g. the default is 1 gigabyte = 2^30 bytes = 1,073,741,824 bytes);arena_used_ratio
=arena_used
/arena_size
;quota_used
is the amount of memory that is already distributed to the slab allocator;arena_size
is the total memory used for tuples and indexes together (including allocated, but currently free slabs);arena_used
is the efficient memory used for storing tuples and indexes together (omitting allocated, but currently free slabs).
Rtype: table
Example:
tarantool> box.slab.info() --- - items_used_ratio: 1.8% quota_size: 1073741824 items_used: 4208 quota_used: 8388608 arena_size: 2325176 arena_used: 1003632 ... tarantool> box.slab.info().arena_used --- - 1003632 ...
-
box.slab.
stats
()¶ Show a detailed memory usage report (in bytes) for the slab allocator. The report is broken down into groups by data item size as well as by slab size (64-byte, 136-byte, etc). The report includes the memory allocated for storing both tuples and indexes.
return: mem_free
is the allocated, but currently unused memory;mem_used
is the memory used for storing data items (tuples and indexes);item_count
is the number of stored items;item_size
is the size of each data item;slab_count
is the number of slabs allocated;slab_size
is the size of each allocated slab.
rtype: table
Example:
Here is a sample report for the first group:
tarantool> box.slab.stats()[1] --- - mem_free: 16232 mem_used: 48 item_count: 2 item_size: 24 slab_count: 1 slab_size: 16384 ...
This report is saying that there are 2 data items (
item_count
= 2) stored in one (slab_count
= 1) 24-byte slab (item_size
= 24), somem_used
= 2 * 24 = 48 bytes. Also,slab_size
is 16384 bytes, of which 16384 - 48 = 16232 bytes are free (mem_free
).A complete report would show memory usage statistics for all groups:
tarantool> box.slab.stats() --- - - mem_free: 16232 mem_used: 48 item_count: 2 item_size: 24 slab_count: 1 slab_size: 16384 - mem_free: 15720 mem_used: 560 item_count: 14 item_size: 40 slab_count: 1 slab_size: 16384 <...> - mem_free: 32472 mem_used: 192 item_count: 1 item_size: 192 slab_count: 1 slab_size: 32768 - mem_free: 1097624 mem_used: 999424 item_count: 61 item_size: 16384 slab_count: 1 slab_size: 2097152 ...
The total
mem_used
for all groups in this report equalsarena_used
in box.slab.info() report.