Redis script for memory flush

I would use a Lua script as it will perform faster, atomically, and it would be easy to use both from redis-cli and any application code.

Here a Lua script to get memory used and maxmemory, the percent, and an action placeholder. It uses both MEMORY STATS and INFO memory to illustrate.

MEMORY STATS brings structured information, but doesn’t include maxmemory or total_system_memory, as INFO memory does. CONFIG GET is not allowed from Lua scripts.

local stats = redis.call('MEMORY', 'STATS')
local memused = 0
for i = 1,table.getn(stats),2 do
    if stats[i] == 'total.allocated' then
        memused = stats[i+1]
        break
    end
end
local meminfo = redis.call('INFO', 'memory')
local maxmemory = 0
for s in meminfo:gmatch('[^\r\n]+') do
    if string.sub(s,1,10) == 'maxmemory:' then
        maxmemory = tonumber(string.sub(s,11))
    end
end
local mempercent = memused/maxmemory
local action = 'No action'
if mempercent > tonumber(ARGV[1]) then
    action = 'Flush here'
end
return {memused, maxmemory, tostring(mempercent), action}

Use as:

> EVAL "local stats = redis.call('MEMORY', 'STATS') n local memused = 0 n for i = 1,table.getn(stats),2 do n     if stats[i] == 'total.allocated' then n     memused = stats[i+1] n break n end n end n local meminfo = redis.call('INFO', 'memory') n local maxmemory = 0 n for s in meminfo:gmatch('[^\r\n]+') do n     if string.sub(s,1,10) == 'maxmemory:' then n     maxmemory = tonumber(string.sub(s,11)) n end n end n local mempercent = memused/maxmemory n local action = 'No action' n if mempercent > tonumber(ARGV[1]) then n     action = 'Flush here' n end n return {memused, maxmemory, tostring(mempercent), action}" 0 0.9
1) (integer) 860264
2) (integer) 100000000
3) "0.00860264"
4) "No action"