#! /usr/bin/awk -f

BEGIN {
     FS = msg_fs ? msg_fs : "|"
    OFS = msg_fs ? msg_fs : "|"
    Kfs = key_fs ? key_fs : ":"
}

# Modify the record we're interested in
$1 == status && $2 == src && ($3 ~ ("^" key_prefix)) {
    key = $3
    val = $4
    prev[key] = curr[key]
    curr[key] = val
    diff[key] = curr[key] - prev[key]
    print($1, $2, $3, diff[key])
    next
}

# Let everything else through untouched
//