diff --git a/playground/block_merge.py b/playground/block_merge.py
new file mode 100644
index 000000000..33c51829a
--- /dev/null
+++ b/playground/block_merge.py
@@ -0,0 +1,277 @@
+'''
+Problem:
+
+- We have N distinct sources of blocks, each with an unknown number of blocks
+  that will eventually be emitted.
+
+- Only M <= N sources are active at the same time. The order in which the
+  sources become active is deterministic. A new source becomes active only
+  when a previously active source is finished.
+
+- We need to find a way to output the blocks in a deterministic order while
+  keeping the number of in-flight blocks to a minimum.
+
+- If a source emits the last block, we know for sure that it's the last block.
+
+Example:
+
+Let's assume N=10 sources and M=4 simultaneously active sources:
+
+  A: 2
+  B: 3
+  C: 9
+  D: 2
+  E: 5
+  F: 3
+  G: 3
+  H: 6
+  I: 1
+  J: 7
+
+Even though we don't know the order in which the blocks will be emitted,
+we can determine the order in which they have to be written up front:
+
+  A1  B1  C1  D1
+  A2* B2  C2  D2*
+  E1  B3* C3  F1
+  E2  G1  C4  F2
+  E3  G2  C5  F3*
+  E4  G3* C6  H1
+  E5  I1* C7  H2
+  J1      C8  H3
+  J2      C9* H4
+  J3          H5
+  J4          H6*
+  J5
+  J6
+  J7*
+
+The order can only be deterministic for a the same number of "slots".
+The order can always be enforced while keeping at most M-1 blocks in
+flight (although more is possible).
+
+We need to know up front which sources exist and what their order is
+going to be. (Not a problem, we know this.)
+
+One issue is that we cannot re-use a slot until we know for sure that
+no previous slot will become available. So we have to wait until all
+previous slots have emitted a block and we know if they can be re-used
+or not.
+
+Blocks can already undergo compression while they're still waiting to
+be deterministically ordered. Ordering is a completely separate process.
+
+Essentially, it looks like the only viable strategy is to block emitters
+until all blocks preceding the block they're trying to emit have been
+processed.
+
+'''
+
+import queue
+import random
+import threading
+import time
+from numpy import random as npr
+
+class source(object):
+    def __init__(self, name):
+        self.__name = name
+        self.__idx = 0
+        self.__num = random.randint(1, 19)
+
+    def next(self):
+        idx = self.__idx
+        self.__idx += 1
+        return (f"{self.__name}.{idx}", self.__idx >= self.__num, npr.exponential(scale = 0.001))
+
+    def name(self):
+        return self.__name
+
+    def blocks(self):
+        return self.__num
+
+    def __repr__(self):
+        return f"{self.__name} -> {self.__idx}/{self.__num}"
+
+def emitter(q, merger):
+    while True:
+        try:
+            s = q.get_nowait()
+        except queue.Empty:
+            break
+
+        while True:
+            block, final, wait = s.next()
+            time.sleep(wait)
+            merger.add(s.name(), block, final, wait)
+            if final:
+                break
+
+class block_merger(object):
+    def __init__(self, slots, sources):
+        self.__slots = slots
+        self.__sources = sources
+        self.__active = []
+        self.__index = 0
+        self.__merged = []
+        self.__blocked = 0
+        self.__total_time = 0
+        self.__total_wait_time = 0
+        self.__cv = threading.Condition()
+        while len(self.__active) < self.__slots and len(self.__sources) > 0:
+            self.__active.append(self.__sources.pop(0))
+
+    def add(self, source, block, final, wait_ONLY_FOR_DEBUGGING):
+        self.__cv.acquire()
+        start = time.time()
+        assert source in self.__active
+        ix = self.__active.index(source)
+        while ix != self.__index:
+            self.__blocked += 1
+            self.__cv.wait()
+        # print(f"{source}, {block}, {final}")
+        self.__merged.append(block)
+        if final:
+            self.__active[ix] = self.__sources.pop(0) if len(self.__sources) > 0 else None
+        while True:
+            self.__index = (self.__index + 1) % self.__slots
+            if self.__index == ix or self.__active[self.__index] is not None:
+                break
+        end = time.time()
+        self.__total_wait_time += end - start
+        self.__total_time += wait_ONLY_FOR_DEBUGGING
+        self.__cv.notify_all()
+        self.__cv.release()
+
+    def total_time(self):
+        return self.__total_time
+
+    def total_wait_time(self):
+        return self.__total_wait_time
+
+    def blocked(self):
+        return self.__blocked
+
+    def merged(self):
+        return self.__merged
+
+class block_merger2(object):
+    def __init__(self, slots, sources, max_per_slot):
+        self.__slots = slots
+        self.__sources = sources
+        self.__source_index = {}
+        self.__queue = []
+        self.__index = 0
+        self.__merged = []
+        self.__blocked = 0
+        self.__total_time = 0
+        self.__total_wait_time = 0
+        self.__cv = threading.Condition()
+        while len(self.__source_index) < self.__slots and len(self.__sources) > 0:
+            self.__source_index[self.__sources.pop(0)] = len(self.__source_index)
+            self.__queue.append(queue.Queue(maxsize=max_per_slot))
+
+    # IDEA: Have queues for each index that elements can already be
+    #       added to. We need some kind of semaphore magic that will
+    #       allow us to have up to a certain number of blocks in flight
+    #       while at the same time making sure we can still generate
+    #       the missing blocks.
+    #       Simple strategy: allow up to Q blocks per slot, with Q
+    #       chosen such that Q < <max-in-flight-blocks>/<slots>.
+
+    def add(self, source, block, final, wait_ONLY_FOR_DEBUGGING):
+        # self.__cv.acquire()
+        start = time.time()
+        assert source in self.__source_index
+        ix = self.__source_index[source]
+        assert self.__queue[ix] is not None
+        self.__queue[ix].put((source, block, final))
+        self.__try_merge()
+        end = time.time()
+        self.__total_wait_time += end - start
+        self.__total_time += wait_ONLY_FOR_DEBUGGING
+        # self.__cv.notify_all()
+        # self.__cv.release()
+
+    def __try_merge(self):
+        try:
+            while True:
+                assert self.__queue[self.__index] is not None
+                source, block, final = self.__queue[self.__index].get_nowait()
+                self.__merged.append(block)
+                if final:
+                    del self.__source_index[source]
+                    if len(self.__sources) > 0:
+                        self.__source_index[self.__sources.pop(0)] = self.__index
+                    else:
+                        self.__queue[self.__index] = None
+                old_ix = self.__index
+                while True:
+                    self.__index = (self.__index + 1) % self.__slots
+                    if self.__index == old_ix or self.__queue[self.__index] is not None:
+                        break
+        except queue.Empty:
+            pass
+
+    def total_time(self):
+        return self.__total_time
+
+    def total_wait_time(self):
+        return self.__total_wait_time
+
+    def blocked(self):
+        return self.__blocked
+
+    def merged(self):
+        return self.__merged
+
+N = 100
+M = 16
+
+for run in range(10):
+    ref = None
+    for rep in range(10):
+        sources = []
+        q = queue.Queue()
+
+        random.seed(run)
+
+        total_blocks = 0
+
+        for si in range(N):
+            s = source(si)
+            total_blocks += s.blocks()
+            sources.append(s.name())
+            q.put(s)
+
+        print(f"==== {run}/{rep} [{total_blocks}] =============")
+
+        merger = block_merger2(slots=M, sources=sources, max_per_slot=1)
+        threads = []
+
+        random.seed()
+
+        t0 = time.time()
+
+        for ei in range(M):
+            t = threading.Thread(target=emitter, args=(q, merger))
+            threads.append(t)
+            t.start()
+
+        for t in threads:
+            t.join()
+
+        t1 = time.time()
+
+        elapsed = len(threads)*(t1 - t0)
+        efficiency = merger.total_time() / elapsed
+
+        print(f"====> {merger.blocked():.3f} / {merger.total_time():.3f} / {merger.total_wait_time():.3f} / {elapsed:.3f} / {efficiency*100:.1f}%")
+
+        if ref is None:
+            ref = merger.merged()
+            assert len(ref) == total_blocks
+            # print(f"{ref}")
+        elif ref != merger.merged():
+            print(f"{merger.merged()}")
+            assert False