Redis sorted sets for leaderboard and ranking

<p>Need a real-time leaderboard that updates as scores change. Querying PostgreSQL for top-N with ORDER BY is expensive at scale. Need O(log N) updates and O(log N + K) range queries.</p>

<p>Use Redis sorted sets (<code>ZADD</code>/<code>ZRANGE</code>) for the leaderboard, sync from PostgreSQL periodically:</p> <div class="highlight"><pre><span></span><code><span class="kn">import</span><span class="w"> </span><span class="nn">json</span> <span class="kn">from</span><span class="w"> </span><span class="nn">redis.asyncio</span><span class="w"> </span><span class="kn">import</span> <span class="n">Redis</span> <span class="n">LEADERBOARD_KEY</span> <span class="o">=</span> <span class="s1">'leaderboard:contributors'</span> <span class="c1"># Update score</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">update_contributor_score</span><span class="p">(</span><span class="n">redis</span><span class="p">:</span> <span class="n">Redis</span><span class="p">,</span> <span class="n">user_id</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">score</span><span class="p">:</span> <span class="nb">float</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kc">None</span><span class="p">:</span> <span class="k">await</span> <span class="n">redis</span><span class="o">.</span><span class="n">zadd</span><span class="p">(</span><span class="n">LEADERBOARD_KEY</span><span class="p">,</span> <span class="p">{</span><span class="n">user_id</span><span class="p">:</span> <span class="n">score</span><span class="p">})</span> <span class="c1"># Get top N with scores</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">get_top_contributors</span><span class="p">(</span><span class="n">redis</span><span class="p">:</span> <span class="n">Redis</span><span class="p">,</span> <span class="n">n</span><span class="p">:</span> <span class="nb">int</span> <span class="o">=</span> <span class="mi">10</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">list</span><span class="p">[</span><span class="nb">dict</span><span class="p">]:</span> <span class="c1"># ZRANGE with REV=True and WITHSCORES</span> <span class="n">entries</span> <span class="o">=</span> <span class="k">await</span> <span class="n">redis</span><span class="o">.</span><span class="n">zrange</span><span class="p">(</span> <span class="n">LEADERBOARD_KEY</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">n</span> <span class="o">-</span> <span class="mi">1</span><span class="p">,</span> <span class="n">rev</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="n">withscores</span><span class="o">=</span><span class="kc">True</span> <span class="p">)</span> <span class="k">return</span> <span class="p">[</span> <span class="p">{</span><span class="s1">'user_id'</span><span class="p">:</span> <span class="n">member</span><span class="o">.</span><span class="n">decode</span><span class="p">(),</span> <span class="s1">'score'</span><span class="p">:</span> <span class="n">score</span><span class="p">}</span> <span class="k">for</span> <span class="n">member</span><span class="p">,</span> <span class="n">score</span> <span class="ow">in</span> <span class="n">entries</span> <span class="p">]</span> <span class="c1"># Get rank of a specific user (0-indexed)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">get_user_rank</span><span class="p">(</span><span class="n">redis</span><span class="p">:</span> <span class="n">Redis</span><span class="p">,</span> <span class="n">user_id</span><span class="p">:</span> <span class="nb">str</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">int</span> <span class="o">|</span> <span class="kc">None</span><span class="p">:</span> <span class="n">rank</span> <span class="o">=</span> <span class="k">await</span> <span class="n">redis</span><span class="o">.</span><span class="n">zrevrank</span><span class="p">(</span><span class="n">LEADERBOARD_KEY</span><span class="p">,</span> <span class="n">user_id</span><span class="p">)</span> <span class="k">return</span> <span class="n">rank</span> <span class="c1"># None if not in leaderboard</span> <span class="c1"># Increment score atomically</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">increment_score</span><span class="p">(</span><span class="n">redis</span><span class="p">:</span> <span class="n">Redis</span><span class="p">,</span> <span class="n">user_id</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">delta</span><span class="p">:</span> <span class="nb">float</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="nb">float</span><span class="p">:</span> <span class="n">new_score</span> <span class="o">=</span> <span class="k">await</span> <span class="n">redis</span><span class="o">.</span><span class="n">zincrby</span><span class="p">(</span><span class="n">LEADERBOARD_KEY</span><span class="p">,</span> <span class="n">delta</span><span class="p">,</span> <span class="n">user_id</span><span class="p">)</span> <span class="k">return</span> <span class="n">new_score</span> <span class="c1"># Sync from PostgreSQL (run on startup and periodically)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">sync_leaderboard</span><span class="p">(</span><span class="n">redis</span><span class="p">:</span> <span class="n">Redis</span><span class="p">,</span> <span class="n">session</span><span class="p">:</span> <span class="n">AsyncSession</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kc">None</span><span class="p">:</span> <span class="n">result</span> <span class="o">=</span> <span class="k">await</span> <span class="n">session</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span> <span class="n">select</span><span class="p">(</span><span class="n">User</span><span class="o">.</span><span class="n">id</span><span class="p">,</span> <span class="n">User</span><span class="o">.</span><span class="n">reputation_score</span><span class="p">)</span> <span class="o">.</span><span class="n">where</span><span class="p">(</span><span class="n">User</span><span class="o">.</span><span class="n">reputation_score</span> <span class="o">&gt;</span> <span class="mi">0</span><span class="p">)</span> <span class="o">.</span><span class="n">order_by</span><span class="p">(</span><span class="n">User</span><span class="o">.</span><span class="n">reputation_score</span><span class="o">.</span><span class="n">desc</span><span class="p">())</span> <span class="o">.</span><span class="n">limit</span><span class="p">(</span><span class="mi">1000</span><span class="p">)</span> <span class="p">)</span> <span class="n">users</span> <span class="o">=</span> <span class="n">result</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="k">if</span> <span class="n">users</span><span class="p">:</span> <span class="k">await</span> <span class="n">redis</span><span class="o">.</span><span class="n">zadd</span><span class="p">(</span> <span class="n">LEADERBOARD_KEY</span><span class="p">,</span> <span class="p">{</span><span class="nb">str</span><span class="p">(</span><span class="n">user</span><span class="o">.</span><span class="n">id</span><span class="p">):</span> <span class="n">user</span><span class="o">.</span><span class="n">reputation_score</span> <span class="k">for</span> <span class="n">user</span> <span class="ow">in</span> <span class="n">users</span><span class="p">}</span> <span class="p">)</span> </code></pre></div> <p><code>ZADD</code> is O(log N), <code>ZRANGE</code> is O(log N + K). Use <code>ZINCRBY</code> for atomic score increments to avoid race conditions.</p>