TStringList of objects taking up tons of memory in

问题:

I'm working on a simulation program.

One of the first things the program does is read in a huge file (28 mb, about 79'000 lines,), parse each line (about 150 fields), create a class for the object, and add it to a TStringList.

It also reads in another file, which adds more objects during the run. At the end, it ends up being about 85'000 objects.

I was working with Delphi 2007, and the program used a lot of memory, but it ran OK. I upgraded to Delphi XE, and migrated the program over and now it's using a LOT more memory, and it ends up running out of memory half way through the run.

So in Delphi 2007, it would end up using 1.4 gigs after reading in the initial file, which is obviously a huge amount, but in XE, it ends up using almost 1.8 gigs, which is really huge and leads to running out and getting the error

So my question is

1. Why is it using so much memory?
2. Why is it using so much more memory in XE than 2007?
3. What can I do about this? I can't change how big or long the file is, and I do need to create an object for each line and to store it somewhere

Thanks

回答1:

It's hard to say why your 28 MB file is expanding to 1.4 GB worth of objects when you parse it out into objects without seeing the code and the class declarations. Also, you say you're storing it in a TStringList instead of a TList or TObjecList. This sounds like you're using it as some sort of string->object key/value mapping. If so, you might want to look at the TDictionary class in the Generics.Collections unit in XE.

As for why you're using more memory in XE, it's because the string type changed from an ANSI string to a UTF-16 string in Delphi 2009. If you don't need Unicode, you could use a TDictionary to save space.

Also, to save even more memory, there's another trick you could use if you don't need all 79,000 of the objects right away: lazy loading. The idea goes something like this:

• Read the file into a TStringList. (This will use about as much memory as the file size. Maybe twice as much if it gets converted into Unicode strings.) Don't create any data objects.
• When you need a specific data object, call a routine that checks the string list and looks up the string key for that object.
• Check if that string has an object associated with it. If not, create the object from the string and associate it with the string in the TStringList.
• Return the object associated with the string.

This will keep both your memory usage and your load time down, but it's only helpful if you don't need all (or a large percentage) of the objects immediately after loading.

回答2:

Just one idea which may save memory.

You could let the data stay on the original files, then just point to them from in-memory structures.

For instance, it's what we do for browsing big log files almost instantly: we memory-map the log file content, then we parse it quick to create indexes of useful information in memory, then we read the content dynamically. No string is created during the reading. Only pointers to each line beginning, with dynamic arrays containing the needed indexes. Calling TStringList.LoadFromFile would be definitively much slower and memory consuming.

The code is here - see the TSynLogFile class. The trick is to read the file only once, and make all indexes on the fly.

For instance, here is how we retrieve a line of text from the UTF-8 file content:

function TMemoryMapText.GetString(aIndex: integer): string;
begin
  if (self=nil) or (cardinal(aIndex)>=cardinal(fCount)) then
    result := '' else
    result := UTF8DecodeToString(fLines[aIndex],GetLineSize(fLines[aIndex],fMapEnd));
end;

We use the exact same trick to parse JSON content. Using such a mixed approach is used by the fastest XML access libraries.

To handle your high-level data, and query them fast, you may try to use dynamic arrays of records, and our optimized TDynArray and TDynArrayHashed wrappers (in the same unit). Arrays of records will be less memory consuming, will be faster to search in because the data won't be fragemented (even faster if you use ordered indexes or hashes), and you'll be able to have high-level access to the content (you can define custom functions to retrieve the data from the memory mapped file, for instance). Dynamic arrays won't fit fast deletion of items (or you'll have to use lookup tables) - but you wrote you are not deleting much data, so it won't be a problem in your case.

So you won't have any duplicated structure any more, only logic in RAM, and data on memory-mapped file(s) - I added a "s" here because the same logic could perfectly map to several source data files (you need some "merge" and "live refresh" AFAIK).

回答3:

• In Delphi 2007 (and earlier), a string is an Ansi string, that is, every character occupies 1 byte of memory.

• In Delphi 2009 (and later), a string is a Unicode string, that is, every character occupies 2 bytes of memory.

AFAIK, there is no way to make a Delphi 2009+ TStringList object use Ansi strings. Are you really using any of the features of the TStringList? If not, you could use an array of strings instead.

Then, naturally, you can choose between

type
  TAnsiStringArray = array of AnsiString;
  // or
  TUnicodeStringArray = array of string; // In Delphi 2009+, 
                                         // string = UnicodeString

回答4:

Reading though the comments, it sounds like you need to lift the data out of Delphi and into a database.

From there it is easy to match organ donors to receivers*)

SELECT pw.* FROM patients_waiting pw
INNER JOIN organs_available oa ON (pw.bloodtype = oa.bloodtype) 
                              AND (pw.tissuetype = oa.tissuetype)
                              AND (pw.organ_needed = oa.organ_offered)
WHERE oa.id = '15484'

If you want to see the patients that might match against new organ-donor 15484.

In memory you only handle the few patients that match.

*) simplified beyond all recognition, but still.

回答5:

In addition to Andreas' post:

Before Delphi 2009, a string header occupied 8 bytes. Starting with Delphi 2009, a string header takes 12 bytes. So every unique string uses 4 bytes more than before, + the fact that each character takes twice the memory.

Also, starting with Delphi 2010 I believe, TObject started using 8 bytes instead of 4. So for each single object created by delphi, delphi now uses 4 more bytes. Those 4 bytes were added to support the TMonitor class I believe.

If you're in desperate need to save memory, here's a little trick that could help if you have a lot of string value that repeats themselve.

var
  uUniqueStrings : TStringList;

function ReduceStringMemory(const S : String) : string;
var idx : Integer;
begin
  if not uUniqueStrings.Find(S, idx) then
    idx := uUniqueStrings.Add(S);

  Result := uUniqueStrings[idx]
end;

Note that this will help ONLY if you have a lot of string values that repeat themselves. For exemple, this code use 150mb less on my system.

var sl : TStringList;
  I: Integer;
begin
  sl := TStringList.Create;
  try
    for I := 0 to 5000000 do
      sl.Add(ReduceStringMemory(StringOfChar('A',5)));every
  finally
    sl.Free;
  end;
end;

回答6:

I also read in a lot of strings in my program that can approach a couple of GB for large files.

Short of waiting for 64-bit XE2, here is one idea that might help you:

I found storing individual strings in a stringlist to be slow and wasteful in terms of memory. I ended up blocking the strings together. My input file has logical records, which may contain between 5 and 100 lines. So instead of storing each line in the stringlist, I store each record. Processing a record to find the line I need adds very little time to my processing, so this is possible for me.

If you don't have logical records, you might just want to pick a blocking size, and store every (say) 10 or 100 strings together as one string (with a delimiter separating them).

The other alternative, is to store them in a fast and efficient on-disk file. The one I'd recommend is the open source Synopse Big Table by Arnaud Bouchez.

回答7:

May I suggest you try using the jedi class library (JCL) class TAnsiStringList, which is like TStringList fromDelphi 2007 in that it is made up of AnsiStrings.

Even then, as others have mentioned, XE will be using more memory than delphi 2007.

I really don't see the value of loading the full text of a giant flat file into a stringlist. Others have suggested a bigtable approach such as Arnaud Bouchez's one, or using SqLite, or something like that, and I agree with them.

I think you could also write a simple class that will load the entire file you have into memory, and provide a way to add line-by-line object links to a giant in-memory ansichar buffer.

回答8:

Starting with Delphi 2009, not only strings but also every TObject has doubled in size. (See Why Has the Size of TObject Doubled In Delphi 2009?). But this would not explain this increase if there are only 85,000 objects. Only if these objects contain many nested objects, their size could be a relevant part of the memory usage.

回答9:

Are there many duplicate strings in your list? Maybe trying to only store unique strings will help reducing the memory size. See my Question about a string pool for a possible (but maybe too simple) answer.

回答10:

Are you sure you don't suffer from a case of memory fragementation?

Be sure to use the latest FastMM (currently 4.97), then take a look at the UsageTrackerDemo demo that contains a memory map form showing the actual usage of the Delphi memory.

Finally take a look at VMMap that shows you how your process memory is used.