15.12.2023, 10:47
This example will change all valid trend values by x2. Recommended way of testing is to create a new trend log with the same parameters as the source.
For counter type the editing is trickier. The stored value is not the actual counter value but a per-second change rate. This example will log the maximum of all stored values without writing to a different trend log file. You can use this value for replacement in the previous script.
Note that when replacing values you should not use direct comparison (==) for floating point values due to possible rounding errors.
Code:
infile = '/tmp/trends/t1.trend'
outfile = '/tmp/trends/t7.trend'
function adjust(value)
value = value * 2
return value
end
ffi = require('ffi')
function stringtodouble(chunk)
local dbl = ffi.new('double[1]')
ffi.copy(dbl, chunk, 8)
return dbl[ 0 ]
end
function doubletostring(val)
local dbl = ffi.new('double[1]')
dbl[ 0 ] = val
return ffi.string(dbl, 8)
end
info = require('rrd').info(infile)
data = io.readfile(infile)
offset = info.header_size
buf = { data:sub(1, offset) }
while true do
chunk = data:sub(offset + 1, offset + 8)
if #chunk == 8 then
value = stringtodouble(chunk)
-- skip NaN (empty/undefined value)
if value == value then
value = adjust(value)
end
buf[ #buf + 1 ] = doubletostring(value)
else
break
end
offset = offset + 8
end
data = table.concat(buf)
io.writefile(outfile, data)For counter type the editing is trickier. The stored value is not the actual counter value but a per-second change rate. This example will log the maximum of all stored values without writing to a different trend log file. You can use this value for replacement in the previous script.
Code:
infile = '/tmp/trends/t1.trend'
max = 0
function check(value)
max = math.max(max, value)
end
ffi = require('ffi')
function stringtodouble(chunk)
local dbl = ffi.new('double[1]')
ffi.copy(dbl, chunk, 8)
return dbl[ 0 ]
end
info = require('rrd').info(infile)
data = io.readfile(infile)
offset = info.header_size
while true do
chunk = data:sub(offset + 1, offset + 8)
if #chunk == 8 then
value = stringtodouble(chunk)
-- skip NaN (empty/undefined value)
if value == value then
check(value)
end
else
break
end
offset = offset + 8
end
log(max)Note that when replacing values you should not use direct comparison (==) for floating point values due to possible rounding errors.