def main(cls, args):
# db = SimpleDB("tabletest", 400, 8)
fm = FileMgr(File("tabletest"), 400)
lm = LogMgr(fm, "simpledb.log")
bm = BufferMgr(fm, lm, 8)
tx = Transaction(fm, lm, bm)
sch = Schema()
sch.addIntField("A")
sch.addStringField("B", 9)
layout = Layout(sch)
for fldname in layout.schema().fields():
offset = layout.offset(fldname)
print(fldname + " has offset " + str(offset))
print("Filling the table with 50 random records.")
ts = TableScan(tx, "T", layout)
for i in range(50):
ts.insert()
n = random.randint(0, 50)
ts.setInt("A", n)
ts.setString("B", "rec" + str(n))
print("inserting into slot " + ts.getRid().__str__() + ": {" +
str(n) + ", " + "rec" + str(n) + "}")
print("Deleting these records, whose A-values are less than 25.")
count = 0
ts.beforeFirst()
while ts.next():
a = ts.getInt("A")
b = ts.getString("B")
if a < 25:
count += 1
print("slot " + ts.getRid().__str__() + ": {" + str(a) + ", " +
b + "}")
ts.delete()
print(str(count) + " values under 10 were deleted.\n")
print("Here are the remaining records.")
ts.beforeFirst()
while ts.next():
a = ts.getInt("A")
b = ts.getString("B")
print("slot " + ts.getRid().__str__() + ": {" + str(a) + ", " + b +
"}")
ts.close()
tx.commit()
class HashIndex(Index):
NUM_BUCKETS = 100
#
# * Opens a hash index for the specified index.
# * @param idxname the name of the index
# * @param sch the schema of the index records
# * @param tx the calling transaction
#
def __init__(self, tx, idxname, layout):
super(HashIndex, self).__init__()
self.tx = tx
self.idxname = idxname
self.layout = layout
#
# * Positions the index before the first index record
# * having the specified search key.
# * The method hashes the search key to determine the bucket,
# * and then opens a table scan on the file
# * corresponding to the bucket.
# * The table scan for the previous bucket (if any) is closed.
# * @see simpledb.index.Index#beforeFirst(simpledb.query.Constant)
#
def beforeFirst(self, searchkey):
self.close()
self.searchkey = searchkey
bucket = searchkey.__hash__() % HashIndex.NUM_BUCKETS
tblname = self.idxname + bucket
self.ts = TableScan(self.tx, tblname, self.layout)
#
# * Moves to the next record having the search key.
# * The method loops through the table scan for the bucket,
# * looking for a matching record, and returning false
# * if there are no more such records.
# * @see simpledb.index.Index#next()
#
def next(self):
while self.ts.next():
if self.ts.getVal("dataval") == self.searchkey:
return True
return False
#
# * Retrieves the dataRID from the current record
# * in the table scan for the bucket.
# * @see simpledb.index.Index#getDataRid()
#
def getDataRid(self):
blknum = self.ts.getInt("block")
_id = self.ts.getInt("id")
return RID(blknum, _id)
#
# * Inserts a new record into the table scan for the bucket.
# * @see simpledb.index.Index#insert(simpledb.query.Constant, simpledb.record.RID)
#
def insert(self, val, rid):
self.beforeFirst(val)
self.ts.insert()
self.ts.setInt("block", rid.blockNumber())
self.ts.setInt("id", rid.slot())
self.ts.setVal("dataval", val)
#
# * Deletes the specified record from the table scan for
# * the bucket. The method starts at the beginning of the
# * scan, and loops through the records until the
# * specified record is found.
# * @see simpledb.index.Index#delete(simpledb.query.Constant, simpledb.record.RID)
#
def delete(self, val, rid):
self.beforeFirst(val)
while self.next():
if self.getDataRid() == rid:
self.ts.delete()
return
#
# * Closes the index by closing the current table scan.
# * @see simpledb.index.Index#close()
#
def close(self):
if self.ts is not None:
self.ts.close()
#
# * Returns the cost of searching an index file having the
# * specified number of blocks.
# * The method assumes that all buckets are about the
# * same size, and so the cost is simply the size of
# * the bucket.
# * @param numblocks the number of blocks of index records
# * @param rpb the number of records per block (not used here)
# * @return the cost of traversing the index
#
@staticmethod
def searchCost(numblocks, rpb):
return numblocks / HashIndex.NUM_BUCKETS
