InterBase MEMO/BLOB fields, data with size > 1MB

From: Pet Kojcista (pet_kojcista_at_hotmail.com)
Date: 05/31/04 

To: dbi-users@perl.org
Date: Mon, 31 May 2004 12:20:02 +0200

    Please help me with this problem (Perl & InterBase MEMO/BLOB fields,
data with size > 1MB):

  I guess someone already had the same problem, so I appreciate any help. In
my Perl script I have a code part that fetches a data from database
InterBase, everything works fine except in case when fetched data has size
of over 1MB! Script(s) work just fine if the "content" in MEMO or BLOB
fields of the database has smaller size than 1MBytes; if size of the file
(data) is over 1MB then "ERROR: Blob exceeds maximum length" is generated in
the "error.log" of the Apache Server (and of course data is not fetched)!

  Script code:
# . . . . . - rest of the code
        use DBI;
# . . . . . - rest of the code
                # name & location of the database
        $dbpath = 'C:\Database\database_01.fdb';
        $dsn = "DBI:InterBase:database=$dbpath;host=123.456.78.9;ib_dialect=3";
                # connesting to DB
        $dbh = DBI->connect($dsn, '', '', {AutoCommit => 0}) or die "$DBI::errstr";
                # setting the size of the buffer (1KB)
        $dbh -> {LongReadLen} = 1024;
                # NO matter if Truncation is ON or OFF? Tried both cases!
        #$dbh -> {LongTrun***} = 0;
        $dbh -> {LongTrun***} = 1;

                # here, DATA is MEMO field in the database!
        $sql = "SELECT FIRST 1 DATA FROM CONFIGURATION ORDER BY CREATEDDATE DESC";
        $sth = $dbh->prepare($sql) or die "Preparing: ", $dbh->errstr;
        $sth->execute or die "Executing: ", $sth->errstr;
                # opening FILE HANDLER for writing the content of the MEMO/BLOB field
        open (F, ">./database1.txt");
                # fetching the content
        while (@row = $sth->fetchrow_array()) {
                foreach (@row) {
                # saving into the file "database1.txt"!
                        print F "$_";
                }
        }
        close F;
        $sth->finish;
        $dbh->commit or warn $dbh->errstr;

# . . . . . - rest of the code

                # here, NAME is CHAR(16) -not so important, while DATA is BLOB field!
        $sql = "SELECT NAME, DATA FROM DOCUMENTS WHERE DOCNAME='$something'";
                # $something was previously defined!
        $sth = $dbh->prepare($sql) or die "Preparing: ", $dbh->errstr;
        $sth->execute or die "Executing: ", $sth->errstr;

        $ii = 1;
        $name = "";
                # fetching the content
        while (@row = $sth->fetchrow_array()) {
                foreach (@row) {
                        if ($ii%2 == 1) {
                # so it is DOKUMENT's NAME!
                                $name = $_;
                        } else {
                # so, this is DATA!
                # opening FILE HANDLER for writing the content of the MEMO/BLOB field
                                open (F, ">./$name");
                                binmode F;
                # saving into the file "base.txt"!
                                print F "$_";
                                close F;
                                $name = "";
                        };
                        $ii++;
                };
        };
        $sth->finish;
        $dbh->commit or warn $dbh->errstr;
        $dbh->disconnect or warn $dbh->errstr;

# . . . . . - rest of the code

  I have tried several workarounds (in the current code I've increased the
size of the buffer, LongReadLen - EVEN to 10MB; also tried with chunks &
blob_read method - to get small pieces of data & to compose/concatenate them
again at the end BUT got nothing, even with data that had size of only
10KB!), everytime it was unsuccessfully! Maybe I should replace the
DBD-InterBase with some other Perl module?
  Installed Environment: Perl version 5.6.1, Firebird 1.5.0 (database:
InterBase) and I have two similar scripts (Win32 & Unix), both work OK when
fetched data had smaller size than 1MB, installed Perl modules: DBI 1.37,
DBD-InterBase 0.40.

   *NOTICE: I read this:
"The DBI currently defines no way to insert or update LONG/LOB values
piece-wise - piece by piece. That means you're limited to handling values
that will fit into your available memory."
   as well as:
"Read/Write BLOB fields block by block not (yet) supported. The maximum size
of a BLOB read/write is hardcoded to about 1MB."
  - Does that mean that I can't get data using DBI and DBD:InterBase with
size larger than 1MB, or how do I change the limit (in DBD:InterBase or in
DBI) from 1MB to 10MB?

   Please help me with any ideas, hints or solutions! Thanks.

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