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ar.py
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ar.py
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"""
Autoregressive (AR) trending as deployed on lbry.tv and
the app right now (Feb 2020).
"""
import copy
import math
import time
# Half life in blocks
HALF_LIFE = 134
# Decay coefficient per block
DECAY = 0.5**(1.0/HALF_LIFE)
# How frequently to write trending values to the db
SAVE_INTERVAL = 10
# Renormalisation interval
RENORM_INTERVAL = 1000
# Assertion
assert RENORM_INTERVAL % SAVE_INTERVAL == 0
# Decay coefficient per renormalisation interval
DECAY_PER_RENORM = DECAY**(RENORM_INTERVAL)
# Log trending calculations?
TRENDING_LOG = True
def install(connection):
"""
Install the AR trending algorithm.
"""
check_trending_values(connection)
if TRENDING_LOG:
f = open("trending_ar.log", "a")
f.close()
# Stub
CREATE_TREND_TABLE = ""
def check_trending_values(connection):
"""
If the trending values appear to be based on the zscore algorithm,
reset them. This will allow resyncing from a standard snapshot.
"""
c = connection.cursor()
needs_reset = False
for row in c.execute("SELECT COUNT(*) num FROM claim WHERE trending_global <> 0;"):
if row[0] != 0:
needs_reset = True
break
if needs_reset:
print("Resetting some columns. This might take a while...", flush=True, end="")
c.execute(""" BEGIN;
UPDATE claim SET trending_group = 0;
UPDATE claim SET trending_mixed = 0;
UPDATE claim SET trending_global = 0;
UPDATE claim SET trending_local = 0;
COMMIT;""")
print("done.")
def spike_height(trending_score, x, x_old, time_boost=1.0):
"""
Compute the size of a trending spike.
"""
# Change in softened amount
change_in_softened_amount = x**0.25 - x_old**0.25
# Softened change in amount
delta = x - x_old
softened_change_in_amount = abs(delta)**0.25
# Softened change in amount counts more for minnows
if delta > 0.0:
if trending_score >= 0.0:
multiplier = 0.1/((trending_score/time_boost + softened_change_in_amount) + 1.0)
softened_change_in_amount *= multiplier
else:
softened_change_in_amount *= -1.0
return time_boost*(softened_change_in_amount + change_in_softened_amount)
def get_time_boost(height):
"""
Return the time boost at a given height.
"""
return 1.0/DECAY**(height % RENORM_INTERVAL)
def trending_log(s):
"""
Log a string.
"""
if TRENDING_LOG:
fout = open("trending_ar.log", "a")
fout.write(s)
fout.flush()
fout.close()
class TrendingData:
"""
An object of this class holds trending data
"""
def __init__(self):
self.claims = {}
# Have all claims been read from db yet?
self.initialised = False
def insert_claim_from_load(self, claim_hash, trending_score, total_amount):
assert not self.initialised
self.claims[claim_hash] = {"trending_score": trending_score,
"total_amount": total_amount,
"changed": False}
def update_claim(self, claim_hash, total_amount, time_boost=1.0):
"""
Update trending data for a claim, given its new total amount.
"""
assert self.initialised
# Extract existing total amount and trending score
# or use starting values if the claim is new
if claim_hash in self.claims:
old_state = copy.deepcopy(self.claims[claim_hash])
else:
old_state = {"trending_score": 0.0,
"total_amount": 0.0,
"changed": False}
# Calculate LBC change
change = total_amount - old_state["total_amount"]
# Modify data if there was an LBC change
if change != 0.0:
spike = spike_height(old_state["trending_score"],
total_amount,
old_state["total_amount"],
time_boost)
trending_score = old_state["trending_score"] + spike
self.claims[claim_hash] = {"total_amount": total_amount,
"trending_score": trending_score,
"changed": True}
def test_trending():
"""
Quick trending test for something receiving 10 LBC per block
"""
data = TrendingData()
data.insert_claim_from_load("abc", 10.0, 1.0)
data.initialised = True
for height in range(1, 5000):
if height % RENORM_INTERVAL == 0:
data.claims["abc"]["trending_score"] *= DECAY_PER_RENORM
time_boost = get_time_boost(height)
data.update_claim("abc", data.claims["abc"]["total_amount"] + 10.0,
time_boost=time_boost)
print(str(height) + " " + str(time_boost) + " " \
+ str(data.claims["abc"]["trending_score"]))
# One global instance
# pylint: disable=C0103
trending_data = TrendingData()
def run(db, height, final_height, recalculate_claim_hashes):
if height < final_height - 5*HALF_LIFE:
trending_log("Skipping AR trending at block {h}.\n".format(h=height))
return
start = time.time()
trending_log("Calculating AR trending at block {h}.\n".format(h=height))
trending_log(" Length of trending data = {l}.\n"\
.format(l=len(trending_data.claims)))
# Renormalise trending scores and mark all as having changed
if height % RENORM_INTERVAL == 0:
trending_log(" Renormalising trending scores...")
keys = trending_data.claims.keys()
for key in keys:
if trending_data.claims[key]["trending_score"] != 0.0:
trending_data.claims[key]["trending_score"] *= DECAY_PER_RENORM
trending_data.claims[key]["changed"] = True
# Tiny becomes zero
if abs(trending_data.claims[key]["trending_score"]) < 1E-9:
trending_data.claims[key]["trending_score"] = 0.0
trending_log("done.\n")
# Regular message.
trending_log(" Reading total_amounts from db and updating"\
+ " trending scores in RAM...")
# Get the value of the time boost
time_boost = get_time_boost(height)
# Update claims from db
if not trending_data.initialised:
# On fresh launch
for row in db.execute("""
SELECT claim_hash, trending_mixed,
(amount + support_amount)
AS total_amount
FROM claim;
"""):
trending_data.insert_claim_from_load(row[0], row[1], 1E-8*row[2])
trending_data.initialised = True
else:
for row in db.execute(f"""
SELECT claim_hash,
(amount + support_amount)
AS total_amount
FROM claim
WHERE claim_hash IN
({','.join('?' for _ in recalculate_claim_hashes)});
""", recalculate_claim_hashes):
trending_data.update_claim(row[0], 1E-8*row[1], time_boost)
trending_log("done.\n")
# Write trending scores to DB
if height % SAVE_INTERVAL == 0:
trending_log(" Writing trending scores to db...")
the_list = []
keys = trending_data.claims.keys()
for key in keys:
if trending_data.claims[key]["changed"]:
the_list.append((trending_data.claims[key]["trending_score"],
key))
trending_data.claims[key]["changed"] = False
trending_log("{n} scores to write...".format(n=len(the_list)))
db.executemany("UPDATE claim SET trending_mixed=? WHERE claim_hash=?;",
the_list)
trending_log("done.\n")
trending_log("Trending operations took {time} seconds.\n\n"\
.format(time=time.time() - start))
if __name__ == "__main__":
test_trending()