Implementation of a database for "Dissecting the humble LSM Tree and SSTable" for SRECon EMEA 2022

LICENSE

The MIT License (MIT)

Copyright (c) 2022 Suhail Patel

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

srecon-emea-2022-db.py

from dataclasses import dataclass
import time
from typing import Optional

@dataclass
class Item(object):
    key: str
    value: Optional[str]
    timestamp: int
    is_deleted: bool = False

    def sort_key(self):
        return (self.key, self.value, self.timestamp, self.is_deleted)

    def to_line(self) -> str:
        deletion = "1" if self.is_deleted else "0"
        value = self.value if self.value else ""
        return f"{self.key},{value},{self.timestamp},{deletion}"

    def from_line(line):
        bag = line.split(',')
        is_deleted = True if bag[3] == "1" else False
        return Item(key=bag[0], value=bag[1], timestamp=int(bag[2]), is_deleted=is_deleted)


class SRECon2022Database(object):
    memtable, sstables = [], []

    def insert(self, key: str, value: str):
        if len(self.memtable) >= 5:
            self.flush()
        self.memtable.append(Item(key=key, value=value, timestamp=time.time_ns()))

    def update(self, key: str, new_value: str):
        self.insert(key, new_value)

    def delete(self, key: str):
        if len(self.memtable) >= 5:
            self.flush()
        self.memtable.append(Item(key=key, value="", timestamp=time.time_ns(), is_deleted=True))

    def flush(self):
        filename = f"fancy-{int(time.time_ns())}-sstable.db"
        with open(filename, "a") as f:
            for item in sorted(self.memtable, key=lambda x: x.sort_key()):
                f.write(item.to_line())
                f.write('\n')

        self.memtable = []
        self.sstables.append(filename)

    def search(self, key) -> Optional[Item]:
        records = []
        
        # Read all our items from our SSTables and find any that match
        # this particular key
        for sstable in self.sstables:
            records.extend(self.search_in_sstable(sstable, key))

        # Read all our records from our Memtable and find any that match
        # this particular key
        records.extend(filter(lambda x: x.key == key, self.memtable))

        # Sort by timestamp ascending so that we can just cherry pick 
        # the last record when evaluating
        records = sorted(records, key=lambda x: x.timestamp)

        # Apply some logic to see what we return:
        # - If we found no matches, return nothing
        # - If our last item was a deletion event, return nothing
        # - Otherwise, return the most recent result
        if not records:
            return None
        elif records[-1].is_deleted:
            return None
        else:
            return records[-1]

    def search_in_sstable(self, sstable, key) -> list[Item]:
        records = []
        with open(sstable) as f:
            for line in f.readlines():
                if not line.strip():
                    continue
                item = Item.from_line(line.strip())
                if item.key == key:
                    records.append(item)
        return records


if __name__ == "__main__":
    db = SRECon2022Database()
    db.insert(key="1", value="a")
    db.insert(key="2", value="b")
    db.insert(key="3", value="c")
    db.insert(key="4", value="d")
    db.insert(key="5", value="e")
    db.insert(key="6", value="f")

    db.update(key="1", new_value="g")
    db.delete(key="3")
    db.flush()

    db.update(key="3", new_value="h")

    print(db.search("1"))
    print(db.search("3"))