I dont have time to write out the code but my approach would be as follows

#open the log
#loop through
$chunk_string = "";
while ($line = <FILE>)
{
    #do any formatting (chomp etc)
    
    if ($line =~ /datestamp/) #appropriate regex here
    {
        if ($chunk_string =~ /whateveryouarelookingfor/)
        {  #you found it in the current chunk }
        $current_datestamp = $1; #update the datestamp
        $line =~ s/$current_datestamp//; #ignore the date
        $chunk_string = ""; #reset the chunk.
    }
    $chunk_string .= $line; #add the line to the current chunk.
}
[download]

It seems like you just want to ignore your datestamp lines:

use strict;
use warnings;

while (<DATA>) {
    next if /\[datestamp\[/;
    print if /crap/;
}
__DATA__
[datestamp] [DEBUG] something here
[datestamp] [DEBUG] something else here
[datestamp] [ERROR] blah blah
<chunk of crap>
[datestamp] [INFO] bla bla bla
[download]

no, cant ignore them this is needed for the script to be able to say something like: there were 17 sqlexception errors within the past 15 mins. or - only 1 suchandsuch error within the past 7 minutes from now. etc

Since you haven't told us how you plan to define which chunk of the log you want to examine, I'm going to leave that part of the coding alone (except to mention that parsing datestamps isn't all that easy - I'm speaking from personal experience here. :) Splitting up the logfile into datestamp-delimited chunks, though, isn't all that tough:

#!/usr/bin/perl -w
use strict;

my ($ts, %store);
while (<DATA>){
    $ts = $1 if /^(\[[^\]]+])/;
    $store{$ts} = $1 if /(DBPoolSQLException:.*)/;
}

for (keys %store){
    # Qualify this with whatever time-stamp matching you want
    print "$_: $store{$_}\n";
}

__END__
[Wed Aug 04 00:10:40.591 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.BLOBJT.cache]: [208973459] Retri
+eve cached object 'segmentProp.map' for segment 142
[Wed Aug 04 00:10:40.591 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.BLOBJT.cache]: [208973459] Retri
+eve cached object 'segmentProp.map' for segment 142

[Wed Aug 04 00:10:40.666 2010] [ERROR] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.DAOBJT]: [208973534] Got an erro
+r executing query "fetchJobQueueTime" chunk "5".
com.boylesoftware.cb2.BLException: Database error in the DAO.

      at com.boylesoftware.cb2.DAO.executeUpdate_Internal(DAO.java:248
+3) [cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.executeNamedQuery(DAO.java:2634) 
+[cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetch_Internal(DAO.java:2524) [cb
+2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetchWithNamedParams(DAO.java:272
+1) [cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetchWithNamedParams(DAO.java:382
+6) [cb2ms.jar:na]
        at com.somecompany.insidetrack.tt.project.ProjConsoleBLO.fetch
+JobQueueTime(ProjConsoleBLO.java:527) [ProjConsoleBLO.class:na]
        at com.somecompany.insidetrack.tt.presentation.workflow.JobOve
+rviewListPE.init(JobOverviewListPE.java:221) [JobOverviewListPE.class
+:na]
        at com.boylesoftware.cb2.presentation.servlet.ShowPageAction.e
+xecute(ShowPageAction.java:141) [cb2ms.jar:na]
        at com.boylesoftware.cb2.presentation.servlet.CB2Action.execut
+e(CB2Action.java:205) [cb2ms.jar:na]
        at org.apache.struts.action.RequestProcessor.processActionPerf
+orm(Unknown Source) [struts.jar:1.1]

        at java.lang.Thread.run(Thread.java:619) [na:1.6.0_16]
Caused by: msjava.dbpool.DBPoolSQLException: The column prefix '#projJ
+ob' does not match with a table name or alias name used in the query.
+ Either the table is not specified in the FROM clause or it has a cor
+relation name which must be used instead.
 (DataSource: insidetrack-db, Type: SYBASE)

[Wed Aug 04 00:10:40.666 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.DAOBJT]: [208973534] executing c
+hunk "6" with a timeout of 360 seconds
[download]

Running the above produces the following:

[Wed Aug 04 00:10:40.666 2010]: DBPoolSQLException: The column prefix 
+'#projJob' does not match with a table name or alias name used in the
+ query. Either the table is not specified in the FROM clause or it ha
+s a correlation name which must be used instead.
[download]

In other words, any chunk that contains a 'DBPoolSQLException' will be stored in the hash and displayed. Again, you should qualify which chunks you want to analyze before you collect the data; otherwise, you'll be flooded with reports.

Here's my try, You may adjust it as you want

#!/usr/bin/perl
use strict;
use warnings;

my %data;
my $CURRENT_DATE = '';
while (<DATA>) {
    chomp;
    if ($_!~m/^\[(Sat|Sun|Mon|Tue|Wed|Fri)/ ) {
        ## keep adding lines into the same array element
        ${ $data{$CURRENT_DATE} }[-1] .= $_;
    }else{
        # We've got a new date? 
        my ($date) = $_=~m/^\[(.*?)\]/;
        $CURRENT_DATE = $date;
        # if we have got that key exists, then we'll push elements
        if (exists $data{$CURRENT_DATE} ) {
            push @{ $data{$CURRENT_DATE} } , $_;
        }else{
            # otherwise, we'll create a key that have array as its val
+ue
            $data{$CURRENT_DATE} = [$_];
        }
    }        
}

print "There were ", scalar @{ $data{'Wed Aug 04 00:10:40.666 2010'} }
+ , " Errors on Wed Aug 04 00:10:40.666 2010\n";

__DATA__
[Wed Aug 04 00:10:40.591 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.BLOBJT.cache]: [208973459] Retri
+eve cached object 'segmentProp.map' for segment 142
[Wed Aug 04 00:10:40.591 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.BLOBJT.cache]: [208973459] Retri
+eve cached object 'segmentProp.map' for segment 142

[Wed Aug 04 00:10:40.666 2010] [ERROR] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.DAOBJT]: [208973534] Got an erro
+r executing query "fetchJobQueueTime" chunk "5".
com.boylesoftware.cb2.BLException: Database error in the DAO.

      at com.boylesoftware.cb2.DAO.executeUpdate_Internal(DAO.java:248
+3) [cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.executeNamedQuery(DAO.java:2634) 
+[cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetch_Internal(DAO.java:2524) [cb
+2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetchWithNamedParams(DAO.java:272
+1) [cb2ms.jar:na]
        at com.boylesoftware.cb2.DAO.fetchWithNamedParams(DAO.java:382
+6) [cb2ms.jar:na]
        at com.somecompany.insidetrack.tt.project.ProjConsoleBLO.fetch
+JobQueueTime(ProjConsoleBLO.java:527) [ProjConsoleBLO.class:na]
        at com.somecompany.insidetrack.tt.presentation.workflow.JobOve
+rviewListPE.init(JobOverviewListPE.java:221) [JobOverviewListPE.class
+:na]
        at com.boylesoftware.cb2.presentation.servlet.ShowPageAction.e
+xecute(ShowPageAction.java:141) [cb2ms.jar:na]
        at com.boylesoftware.cb2.presentation.servlet.CB2Action.execut
+e(CB2Action.java:205) [cb2ms.jar:na]
        at org.apache.struts.action.RequestProcessor.processActionPerf
+orm(Unknown Source) [struts.jar:1.1]

        at java.lang.Thread.run(Thread.java:619) [na:1.6.0_16]
Caused by: msjava.dbpool.DBPoolSQLException: The column prefix '#projJ
+ob' does not match with a table name or alias name used in the query.
+ Either the table is not specified in the FROM clause or it has a cor
+relation name which must be used instead.
 (DataSource: insidetrack-db, Type: SYBASE)

[Wed Aug 04 00:10:40.666 2010] [DEBUG] [TP-Processor19, time=128089504
+0587, uri=/ibdsupport/workflow/webapp/workflow/coordinator/gotoCoordi
+natorNew.cb2] [com.boylesoftware.cb2.DAOBJT]: [208973534] executing c
+hunk "6" with a timeout of 360 seconds
[download]

use warnings;
use strict;

my $i = -1;
my @chunks;

while (<DATA>)
{
    ++$i if /^\[.+?\] \[[A-Z]+\]/;
    $chunks[$i] .= $_ if $i >= 0;
}

print grep { /DBPoolSQLException/ } @chunks;
[download]