Fast extraction of a time range from syslog logfile?

Update: I've replaced the original code with an updated version with numerous improvements. Let's call this (actual?)alpha-quality.

This version includes:

• command-line option handling
• command-line date format validation
• some try blocks
• line reading moved into a function

Original text:

Well what do you know? "Seek" and ye shall find! Here is a Python program that seeks around in the file and uses a more-or-less binary search. It's considerably faster than that AWK script that other guy wrote.

It's (pre?)alpha-quality. It should have try blocks and input validation and lots of testing and could no doubt be more Pythonic. But here it is for your amusement. Oh, and it's written for Python 2.6.

New code:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# timegrep.py by Dennis Williamson 20100113
# in response to http://serverfault.com/questions/101744/fast-extraction-of-a-time-range-from-syslog-logfile

# thanks to serverfault user http://serverfault.com/users/1545/mike
# for the inspiration

# Perform a binary search through a log file to find a range of times
# and print the corresponding lines

# tested with Python 2.6

# TODO: Make sure that it works if the seek falls in the middle of
#       the first or last line
# TODO: Make sure it's not blind to a line where the sync read falls
#       exactly at the beginning of the line being searched for and
#       then gets skipped by the second read
# TODO: accept arbitrary date

# done: add -l long and -s short options
# done: test time format

version = "0.01a"

import os, sys
from stat import *
from datetime import date, datetime
import re
from optparse import OptionParser

# Function to read lines from file and extract the date and time
def getdata():
    """Read a line from a file

    Return a tuple containing:
        the date/time in a format such as 'Jan 15 20:14:01'
        the line itself

    The last colon and seconds are optional and
    not handled specially

    """
    try:
        line = handle.readline(bufsize)
    except:
        print("File I/O Error")
        exit(1)
    if line == '':
        print("EOF reached")
        exit(1)
    if line[-1] == '\n':
        line = line.rstrip('\n')
    else:
        if len(line) >= bufsize:
            print("Line length exceeds buffer size")
        else:
            print("Missing newline")
        exit(1)
    words = line.split(' ')
    if len(words) >= 3:
        linedate = words[0] + " " + words[1] + " " + words[2]
    else:
        linedate = ''
    return (linedate, line)
# End function getdata()

# Set up option handling
parser = OptionParser(version = "%prog " + version)

parser.usage = "\n\t%prog [options] start-time end-time filename\n\n\
\twhere times are in the form hh:mm[:ss]"

parser.description = "Search a log file for a range of times occurring yesterday \
and/or today using the current time to intelligently select the start and end. \
A date may be specified instead. Seconds are optional in time arguments."

parser.add_option("-d", "--date", action = "store", dest = "date",
                default = "",
                help = "NOT YET IMPLEMENTED. Use the supplied date instead of today.")

parser.add_option("-l", "--long", action = "store_true", dest = "longout",
                default = False,
                help = "Span the longest possible time range.")

parser.add_option("-s", "--short", action = "store_true", dest = "shortout",
                default = False,
                help = "Span the shortest possible time range.")

parser.add_option("-D", "--debug", action = "store", dest = "debug",
                default = 0, type = "int",
                help = "Output debugging information.\t\t\t\t\tNone (default) = %default, Some = 1, More = 2")

(options, args) = parser.parse_args()

if not 0 <= options.debug <= 2:
    parser.error("debug level out of range")
else:
    debug = options.debug    # 1 = print some debug output, 2 = print a little more, 0 = none

if options.longout and options.shortout:
    parser.error("options -l and -s are mutually exclusive")

if options.date:
    parser.error("date option not yet implemented")

if len(args) != 3:
    parser.error("invalid number of arguments")

start = args[0]
end   = args[1]
file  = args[2]

# test for times to be properly formatted, allow hh:mm or hh:mm:ss
p = re.compile(r'(^[2][0-3]|[0-1][0-9]):[0-5][0-9](:[0-5][0-9])?$')

if not p.match(start) or not p.match(end):
    print("Invalid time specification")
    exit(1)

# Determine Time Range
yesterday = date.fromordinal(date.today().toordinal()-1).strftime("%b %d")
today     = datetime.now().strftime("%b %d")
now       = datetime.now().strftime("%R")

if start > now or start > end or options.longout or options.shortout:
    searchstart = yesterday
else:
    searchstart = today

if (end > start > now and not options.longout) or options.shortout:
    searchend = yesterday
else:
    searchend = today

searchstart = searchstart + " " + start
searchend = searchend + " " + end

try:
    handle = open(file,'r')
except:
    print("File Open Error")
    exit(1)

# Set some initial values
bufsize = 4096  # handle long lines, but put a limit them
rewind  =  100  # arbitrary, the optimal value is highly dependent on the structure of the file
limit   =   75  # arbitrary, allow for a VERY large file, but stop it if it runs away
count   =    0
size    =    os.stat(file)[ST_SIZE]
beginrange   = 0
midrange     = size / 2
oldmidrange  = midrange
endrange     = size
linedate     = ''

pos1 = pos2  = 0

if debug > 0: print("File: '{0}' Size: {1} Today: '{2}' Now: {3} Start: '{4}' End: '{5}'".format(file, size, today, now, searchstart, searchend))

# Seek using binary search
while pos1 != endrange and oldmidrange != 0 and linedate != searchstart:
    handle.seek(midrange)
    linedate, line = getdata()    # sync to line ending
    pos1 = handle.tell()
    if midrange > 0:             # if not BOF, discard first read
        if debug > 1: print("...partial: (len: {0}) '{1}'".format((len(line)), line))
        linedate, line = getdata()

    pos2 = handle.tell()
    count += 1
    if debug > 0: print("#{0} Beg: {1} Mid: {2} End: {3} P1: {4} P2: {5} Timestamp: '{6}'".format(count, beginrange, midrange, endrange, pos1, pos2, linedate))
    if  searchstart > linedate:
        beginrange = midrange
    else:
        endrange = midrange
    oldmidrange = midrange
    midrange = (beginrange + endrange) / 2
    if count > limit:
        print("ERROR: ITERATION LIMIT EXCEEDED")
        exit(1)

if debug > 0: print("...stopping: '{0}'".format(line))

# Rewind a bit to make sure we didn't miss any
seek = oldmidrange
while linedate >= searchstart and seek > 0:
    if seek < rewind:
        seek = 0
    else:
        seek = seek - rewind
    if debug > 0: print("...rewinding")
    handle.seek(seek)

    linedate, line = getdata()    # sync to line ending
    if debug > 1: print("...junk: '{0}'".format(line))

    linedate, line = getdata()
    if debug > 0: print("...comparing: '{0}'".format(linedate))

# Scan forward
while linedate < searchstart:
    if debug > 0: print("...skipping: '{0}'".format(linedate))
    linedate, line = getdata()

if debug > 0: print("...found: '{0}'".format(line))

if debug > 0: print("Beg: {0} Mid: {1} End: {2} P1: {3} P2: {4} Timestamp: '{5}'".format(beginrange, midrange, endrange, pos1, pos2, linedate))

# Now that the preliminaries are out of the way, we just loop,
#     reading lines and printing them until they are
#     beyond the end of the range we want

while linedate <= searchend:
    print line
    linedate, line = getdata()

if debug > 0: print("Start: '{0}' End: '{1}'".format(searchstart, searchend))
handle.close()

This will print the range of entries between a start time and an end time based on how they relate to the current time ("now").

Usage:

timegrep [-l] start end filename

Example:

$ timegrep 18:47 03:22 /some/log/file

The -l (long) option causes the longest possible output. The start time will be interpreted as yesterday if the hours and minutes value of the start time is less than both the end time and now. The end time will be interpreted as today if both the start time and end time HH:MM values are greater than "now".

Assuming that "now" is "Jan 11 19:00", this is how various example start and end times will be interpreted (without -l except as noted):

start    end      range begin    range end
19:01    23:59    Jan 10         Jan 10
19:01    00:00    Jan 10         Jan 11
00:00    18:59    Jan 11         Jan 11
18:59    18:58    Jan 10         Jan 10
19:01    23:59    Jan 10         Jan 11        # -l
00:00    18:59    Jan 10         Jan 11        # -l
18:59    19:01    Jan 10         Jan 11        # -l

Almost all of the script is setup. The last two lines do all the work.

Warning: no argument validation or error checking is done. Edge cases have not been thoroughly tested. This was written using gawk other versions of AWK may squawk.

#!/usr/bin/awk -f
BEGIN {
    arg=1
    if ( ARGV[arg] == "-l" ) {
        long = 1
        ARGV[arg++] = ""
    }
    start = ARGV[arg]
    ARGV[arg++] = ""
    end = ARGV[arg]
    ARGV[arg++] = ""

    yesterday = strftime("%b %d", mktime(strftime("%Y %m %d -24 00 00")))
    today = strftime("%b %d")
    now = strftime("%R")

    if ( start > now || start > end || long )
        startdate = yesterday
    else
        startdate = today

    if ( end > now && end > start && start > now && ! long )
        enddate = yesterday
    else
        enddate = today
    fi

startdate = startdate " " start
enddate = enddate " " end
}

$1 " " $2 " " $3 > enddate {exit}
$1 " " $2 " " $3 >= startdate {print}

I think AWK is very efficient at searching through files. I don't think anything else is necessarily going to be any faster at searching an unindexed text file.

From a quick search on the net, there are things that extract based upon keywords (like FIRE or such :) but nothing that extracts a date range from the file.

It does not seem hard to do what you propose:

1. Search for the starting time.
2. Print out that line.
3. If the ending time < start time, and a line's date is > end and < start, then stop.
4. If the ending time is > start time, and a line's date is > end, stop.

Seems straight forward, and I could write it for you if you don't mind Ruby :)

A C++ program applying a binary search - it would need some simple modifications (i.e. calling strptime) to work with text dates.

http://gitorious.org/bs_grep/

I had a previous version with support for text dates, however it was still too slow for the scale of our log files; profiling said that over 90% of the time was spent in strptime, so, we just modified the log format to include a numeric unix timestamp as well.

Even though this answer is way too late, it might be beneficial to some.

I've converted the code from @Dennis Williamson into a Python class that can be used for other python stuff.

I've added support for multiple date supports.

import os
from stat import *
from datetime import date, datetime
import re

# @TODO Support for rotated log files - currently using the current year for 'Jan 01' dates.
class LogFileTimeParser(object):
    """
    Extracts parts of a log file based on a start and enddate
    Uses binary search logic to speed up searching

    Common usage: validate log files during testing

    Faster than awk parsing for big log files
    """
    version = "0.01a"

    # Set some initial values
    BUF_SIZE = 4096  # self.handle long lines, but put a limit to them
    REWIND = 100  # arbitrary, the optimal value is highly dependent on the structure of the file
    LIMIT = 75  # arbitrary, allow for a VERY large file, but stop it if it runs away

    line_date = ''
    line = None
    opened_file = None

    @staticmethod
    def parse_date(text, validate=True):
        # Supports Aug 16 14:59:01 , 2016-08-16 09:23:09 Jun 1 2005  1:33:06PM (with or without seconds, miliseconds)
        for fmt in ('%Y-%m-%d %H:%M:%S %f', '%Y-%m-%d %H:%M:%S', '%Y-%m-%d %H:%M',
                    '%b %d %H:%M:%S %f', '%b %d %H:%M', '%b %d %H:%M:%S',
                    '%b %d %Y %H:%M:%S %f', '%b %d %Y %H:%M', '%b %d %Y %H:%M:%S',
                    '%b %d %Y %I:%M:%S%p', '%b %d %Y %I:%M%p', '%b %d %Y %I:%M:%S%p %f'):
            try:
                if fmt in ['%b %d %H:%M:%S %f', '%b %d %H:%M', '%b %d %H:%M:%S']:

                    return datetime.strptime(text, fmt).replace(datetime.now().year)
                return datetime.strptime(text, fmt)
            except ValueError:
                pass
        if validate:
            raise ValueError("No valid date format found for '{0}'".format(text))
        else:
            # Cannot use NoneType to compare datetimes. Using minimum instead
            return datetime.min

    # Function to read lines from file and extract the date and time
    def read_lines(self):
        """
        Read a line from a file
        Return a tuple containing:
            the date/time in a format supported in parse_date om the line itself
        """
        try:
            self.line = self.opened_file.readline(self.BUF_SIZE)
        except:
            raise IOError("File I/O Error")
        if self.line == '':
            raise EOFError("EOF reached")
        # Remove \n from read lines.
        if self.line[-1] == '\n':
            self.line = self.line.rstrip('\n')
        else:
            if len(self.line) >= self.BUF_SIZE:
                raise ValueError("Line length exceeds buffer size")
            else:
                raise ValueError("Missing newline")
        words = self.line.split(' ')
        # This results into Jan 1 01:01:01 000000 or 1970-01-01 01:01:01 000000
        if len(words) >= 3:
            self.line_date = self.parse_date(words[0] + " " + words[1] + " " + words[2],False)
        else:
            self.line_date = self.parse_date('', False)
        return self.line_date, self.line

    def get_lines_between_timestamps(self, start, end, path_to_file, debug=False):
        # Set some initial values
        count = 0
        size = os.stat(path_to_file)[ST_SIZE]
        begin_range = 0
        mid_range = size / 2
        old_mid_range = mid_range
        end_range = size
        pos1 = pos2 = 0

        # If only hours are supplied
        # test for times to be properly formatted, allow hh:mm or hh:mm:ss
        p = re.compile(r'(^[2][0-3]|[0-1][0-9]):[0-5][0-9](:[0-5][0-9])?$')
        if p.match(start) or p.match(end):
            # Determine Time Range
            yesterday = date.fromordinal(date.today().toordinal() - 1).strftime("%Y-%m-%d")
            today = datetime.now().strftime("%Y-%m-%d")
            now = datetime.now().strftime("%R")
            if start > now or start > end:
                search_start = yesterday
            else:
                search_start = today
            if end > start > now:
                search_end = yesterday
            else:
                search_end = today
            search_start = self.parse_date(search_start + " " + start)
            search_end = self.parse_date(search_end + " " + end)
        else:
            # Set dates
            search_start = self.parse_date(start)
            search_end = self.parse_date(end)
        try:
            self.opened_file = open(path_to_file, 'r')
        except:
            raise IOError("File Open Error")
        if debug:
            print("File: '{0}' Size: {1} Start: '{2}' End: '{3}'"
                  .format(path_to_file, size, search_start, search_end))

        # Seek using binary search -- ONLY WORKS ON FILES WHO ARE SORTED BY DATES (should be true for log files)
        try:
            while pos1 != end_range and old_mid_range != 0 and self.line_date != search_start:
                self.opened_file.seek(mid_range)
                # sync to self.line ending
                self.line_date, self.line = self.read_lines()
                pos1 = self.opened_file.tell()
                # if not beginning of file, discard first read
                if mid_range > 0:
                    if debug:
                        print("...partial: (len: {0}) '{1}'".format((len(self.line)), self.line))
                    self.line_date, self.line = self.read_lines()
                pos2 = self.opened_file.tell()
                count += 1
                if debug:
                    print("#{0} Beginning: {1} Mid: {2} End: {3} P1: {4} P2: {5} Timestamp: '{6}'".
                          format(count, begin_range, mid_range, end_range, pos1, pos2, self.line_date))
                if search_start > self.line_date:
                    begin_range = mid_range
                else:
                    end_range = mid_range
                old_mid_range = mid_range
                mid_range = (begin_range + end_range) / 2
                if count > self.LIMIT:
                    raise IndexError("ERROR: ITERATION LIMIT EXCEEDED")
            if debug:
                print("...stopping: '{0}'".format(self.line))
            # Rewind a bit to make sure we didn't miss any
            seek = old_mid_range
            while self.line_date >= search_start and seek > 0:
                if seek < self.REWIND:
                    seek = 0
                else:
                    seek -= self.REWIND
                if debug:
                    print("...rewinding")
                self.opened_file.seek(seek)
                # sync to self.line ending
                self.line_date, self.line = self.read_lines()
                if debug:
                    print("...junk: '{0}'".format(self.line))
                self.line_date, self.line = self.read_lines()
                if debug:
                    print("...comparing: '{0}'".format(self.line_date))
            # Scan forward
            while self.line_date < search_start:
                if debug:
                    print("...skipping: '{0}'".format(self.line_date))
                self.line_date, self.line = self.read_lines()
            if debug:
                print("...found: '{0}'".format(self.line))
            if debug:
                print("Beginning: {0} Mid: {1} End: {2} P1: {3} P2: {4} Timestamp: '{5}'".
                      format(begin_range, mid_range, end_range, pos1, pos2, self.line_date))
            # Now that the preliminaries are out of the way, we just loop,
            # reading lines and printing them until they are beyond the end of the range we want
            while self.line_date <= search_end:
                # Exclude our 'Nonetype' values
                if not self.line_date == datetime.min:
                    print self.line
                self.line_date, self.line = self.read_lines()
            if debug:
                print("Start: '{0}' End: '{1}'".format(search_start, search_end))
            self.opened_file.close()
        # Do not display EOFErrors:
        except EOFError as e:
            pass