Copy/delete issue

I have a strange situation that occurs every now and again.

We have a reports system that gathers all the data from our various
production systems during the night, where we can run heavy reports on
it without loading the production databases.

I have two shell scripts that do this nightly transfer of data. The
production database is Sybase. So I have a shell script that scans a
list of tables and databases and dumps them into a format suitable for
postgres COPY. After it dumps everything, another shell script scans the
same list, and loads each dump file into the proper table.

The shell script first runs psql with a DELETE command. For transaction
tables (ones where data accumulates by date) the records for two days
are deleted, and for non-transaction tables (ones that have records that
might change but don't accumulate based on time) it's DELETE without WHERE.

I run psql with ON_ERROR_STOP and check the exit status. If the DELETE
failed, I should get an error status, so I do not proceed to the copy.

Then I run psql again, with ON_ERROR_STOP, and run a \copy command that
loads the data to the same table.

For some reason, once in a while, that fails. Always on the same table -
violating the unique constraint of the primary key. Now, this is
impossible because there was a successful delete beforehand, as I said,
and the data comes from a database where that same primary key is
enforced. Moreover, when I re-run the script, everything runs fine.

This happens at least once a week - always with the same table.

Can anybody think of a reason why psql will not report an error on
deletion? Or why it would tell me that a constraint has been violated
when loading the same data 5 minutes later works fine?

Thanks,
Herouth

Here is the relevant shell code (the relevant table has "*' in the file
for datefield):

# The names of the tables are stored in a text file

exec 4<$TABLES_FILE

dstamp N "Starting postgres load" >> $LOAD_LOG

while read -u 4 ignored1 ignored2 local_table datefield
do
dstamp N "Now loading $local_table" >> $LOAD_LOG

filename="$DUMPDIR/$local_table.tsv"

# Stop if the dump file does not exist.

if [ ! -f "$filename" ]
then
errexit "Dump file not found for table: $local_table" 1 >> $LOAD_LOG
fi

# If the datefield contains "*", it means the table contents are fully
# replaced, otherwise use this as the field on which to limit the
deletion.

if [ "$datefield" = "*" ]
then
CMD="DELETE FROM $local_table"
else
CMD="DELETE FROM $local_table WHERE $datefield >= current_date - 2"
fi

# Run the deletion command

echo -e "\\\\set ON_ERROR_STOP\\n$CMD;" | $PSQLCMD -q -f - >
$TMPFILE 2>&1

# Report errors and stop the loop if any occured

rc=$?

if [ "$rc" != "0" ]
then

# Copy the error output, properly formatted, to the log file

sed "s/^/$(date +%Y-%m-%d%t%T) E /" $TMPFILE >> $LOAD_LOG

# Send mail message about the failure

rm -f $TMPFILE

errexit "Deletion failed with status $rc on table: $local_table"
$rc >> $LOAD_LOG

fi

# Now run the load command

echo -e "\\\\set ON_ERROR_STOP\\n\\\\copy $local_table from
$filename" | $PSQLCMD -q -f - > $TMPFILE 2>&1

rc=$?

# Check for errors and report

if [ "$rc" != "0" ]
then

# Copy the error output, properly formatted, to the log file

sed "s/^/$(date +%Y-%m-%d%t%T) E /" $TMPFILE >> $LOAD_LOG

# Send mail message about the failure

rm -f $TMPFILE
errexit "Copy failed with status $rc on table: $local_table" $rc
>> $LOAD_LOG
fi

# Remove the dump file, as well as the output file from the psql command

rm -f "$filename"

# Update statistics with the ANALYZE command

dstamp N "Updating statistics for $local_table" >> $LOAD_LOG

echo -e "\\\\set ON_ERROR_STOP\\nANALYZE $local_table;" | $PSQLCMD
-q -f - > $TMPFILE 2>&1

# Report errors and stop the loop if any occured

rc=$?

if [ "$rc" != "0" ]
then

# Copy the error output, properly formatted, to the log file

sed "s/^/$(date +%Y-%m-%d%t%T) E /" $TMPFILE >> $LOAD_LOG

# Send mail message about the failure

rm -f $TMPFILE

errexit "ANALYZE failed with status $rc on table: $local_table"
$rc >> $LOAD_LOG

fi

done