Class: CacheManager

# File lib/storage/cache.rb, line 112
  def initialize(db)
    @cwidth = options['cache_width']
    @cdepth = options['cache_depth']

    @db =  db
    @st = CacheStats.new

    @cache = Array.new(@cwidth) {Array.new}
    @cwidth.times do |i|
      @cdepth.times do |j|
        @cache[i] << CacheEntry.new
        @st.inc(:cache_size)
      end
    end

  end

delete(oid)

delete an object

[Source]

# File lib/storage/cache.rb, line 254
  def delete(oid)
    return nil if oid.nil?
    @st.inc(:deletes)
    hv = hash(oid)

    # mark dead in cache

    @cache[hv].each do |ce|
      next if ce.oid != oid
      ce.mark_dead
      break
    end
    # delete it from the database

    @db.delete(oid.to_s)
  end

get(oid)

gets an object

oid: - integer object id to retrieve
return: - a reference to the object or nil if none exists

[Source]

# File lib/storage/cache.rb, line 151
  def get(oid)
    return nil if oid.nil?
    @st.inc(:reads)
    hv = hash(oid)

    # search the cache

    @cache[hv].each do |ce|
      if ce.oid == oid
        @st.inc(:cache_read_hits)
        # need to try putting hot hit to the head of the list?

        return ce.obj
      end
    end

    # cache miss - search the database

    if @db.has_key? oid.to_s
      ret = Utility.decode(@db[oid.to_s])
    else
      @st.inc(:database_read_fails)
      return nil
    end
    @st.inc(:database_reads)

    # get and remove the last entry off this list

    ch = @cache[hv].pop
    # if its dirty we write it to the database

    if ch.dirty? && !ch.dead?
      @db[ch.oid.to_s] = Utility.encode(ch.obj)
      @st.inc(:database_writes)
      if ch.noswap?  # here we have a problem we can't use this

        # first push it back onto the list

        @cache[hv].unshift ch
        # get ourselves a brand new

        ch = CacheEntry.new
        # problem solved

        # the depth of any list chains will be cache_depth + # noswap entries

      end
    end

    # assign our new object to the cache entry

    ch.obj = ret
    ch.oid = oid
    ch.clean!
    # push it to the head of the list

    @cache[hv].unshift ch

    ret
  end

hash(oid)

Our simple hash algoritm. Our database keys are sequentially assigned integers, so… I don‘t know what would be better.

[Source]

# File lib/storage/cache.rb, line 144
  def hash(oid)
    oid % @cwidth
  end

inspect()

report on the cache map see cmd_dumpcache

[Source]

# File lib/storage/cache.rb, line 130
  def inspect
    str = "cache width:#{@cwidth} cache depth:#{@cdepth}\n"
    @cwidth.times do |i|
      @cache[i].each_with_index do |ce,j|
        next if ce.dead?
        str << "cache map [#{i}][#{j}] => "
        str << "oid #{ce.oid} object_id #{ce.obj.object_id} dirty? #{ce.dirty?}  noswap? #{ce.noswap?}\n"
      end
    end
    str
  end

keys()

This is provided to traverse the entire object chain. This thrashes the cache violently. See Store#each. One needs to question the design of routines that use Store#each above.

[Source]

# File lib/storage/cache.rb, line 359
  def keys
    kys = []
    @cwidth.times do |i|
      @cache[i].each {|ce| kys << ce.oid if !ce.oid.nil? }
    end
    kys
  end

makenoswap(oid)

Mark an object in the cache as nonswappable

oid: is the object id
return: undefined

[Source]

# File lib/storage/cache.rb, line 319
  def makenoswap(oid)
    return nil if oid.nil?
    @st.inc(:cache_noswap)
    hv = hash(oid)

    @cache[hv].each do |ce|
      next if ce.oid != oid
      ce.noswap!
      return
    end

    # This would indicate we've tried marking it noswap before we did a put.

    # A logic error

    @st.inc(:cache_noswap_misses)
    log.debug "Marking object nonswappable before put - #{oid}"
  end

makeswap(oid)

Mark an object in the cache as swappable

oid: is the object id
return: undefined

[Source]

# File lib/storage/cache.rb, line 339
  def makeswap(oid)
    return nil if oid.nil?
    @st.inc(:cache_swap)
    hv = hash(oid)

    @cache[hv].each do |ce|
      next if ce.oid != oid
      ce.swap!
      return
    end

    # This would indicate we've tried marking it swap before we did a put.

    # A logic error

    @st.inc(:cache_swap_misses)
    log.debug "Marking object swappable before put - #{oid}"
  end

mark(oid)

deliberately mark an object in the cache as dirty see properties.

[Source]

# File lib/storage/cache.rb, line 271
  def mark(oid)
    return nil if oid.nil?
    @st.inc(:cache_marks)
    hv = hash(oid)

    @cache[hv].each do |ce|
      next if ce.oid != oid
      ce.dirty!
      return
    end

    # this would indicate we've tried marking it dirty before we did a put.

    @st.inc(:cache_mark_misses)
    log.debug "Marking object dirty before put - #{oid}"
  end

put(obj)

puts an object

obj: - The integer object id to retrieve
return: - undefined

[Source]

# File lib/storage/cache.rb, line 203
  def put(obj)
    return nil if obj.nil?
    @st.inc(:writes)
    hv = hash(obj.id)

    # search the cache

    @cache[hv].each do |ce|
      next if ce.oid != obj.id
      @st.inc(:cache_write_hits) if ce.dirty?
      if obj.object_id != ce.obj.object_id  # be safe

        # Be extra careful here.  It's possible we could have two objects

        # with the same object id but with different Ruby object_ids.

        # Most likely this is a bug, but we should handle it here..

        ce.obj = obj
        log.warn "Duplicate object id's in cache!"
        log.warn "insert - #{obj.inspect}"
        log.warn "cache - #{obj.inspect}"
      end
      # need to try putting hot hit to the head of the list?

      ce.dirty!
      return
    end

    # get and remove the last entry off this list

    ch = @cache[hv].pop
    # if its dirty we write it to the database

    if ch.dirty? && !ch.dead?
      # errors possible - check in store module

      @db[ch.oid.to_s] = Utility.encode(ch.obj)
      @st.inc(:database_writes)
      if ch.noswap?  # here we have a problem we can't use this

        # first push it back onto the list

        @cache[hv].unshift ch
        # get ourselves a brand new

        ch = CacheEntry.new
        # problem solved

        # the depth of any list chains will be cache_depth + # noswap entries

      end
    end

    # assign our new object to the cache entry

    ch.obj = obj
    ch.oid = obj.id
    ch.dirty!
    # push it to the head of the list

    @cache[hv].unshift ch

    return
  end

stats()

produce a report - see cmd_stats

[Source]

# File lib/storage/cache.rb, line 368
  def stats
    str =  "----------* Cache Statistics *----------\n"
    @st.each do |k,v|
      str << sprintf("%25-25s : %d\n",k.to_s.gsub(/_/,' '),v)
    end
    str << "----------*                  *----------\n"
  end

sync()

syncronize the entire cache with the database called by save.

[Source]

# File lib/storage/cache.rb, line 289
  def sync
    @st.inc(:cache_syncs)
    # search the list chains for dirty objects and write them out.

    @cwidth.times do |i|
      @cache[i].each do |ce|
        if ce.dirty?
          @db[ce.oid.to_s] = Utility.encode(ce.obj)
          @st.inc(:database_writes)
          ce.clean!
        end
      end
    end
  end

sync_chain(i)

syncronize a specific list chain not yet called but included for possible performance enhancement

[Source]

# File lib/storage/cache.rb, line 305
  def sync_chain(i)
    @st.inc(:chain_syncs)
    @cache[i].each do |ce|
      if ce.dirty?
        @db[ce.oid.to_s] = Utility.encode(ce.obj)
        @st.inc(:database_writes)
        ce.clean!
      end
    end
  end

Methods

Public Class methods

Public Instance methods