add SQLite concurrency tests and bench task

BenchRepo for isolated concurrency testing against temp DB files.
Correctness tests prove WAL concurrent reads, IMMEDIATE transaction
mode vs DEFERRED upgrade failures, and PRAGMA application. Benchmark
tests (tagged :benchmark, excluded by default) measure throughput.

mix bench.sqlite runs HTTP load scenarios against the full Phoenix
stack with --prod, --scale, --pool-size, and --busy-timeout options.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
jamey 2026-02-22 09:23:36 +00:00
parent 04cdb62a8d
commit 162bf4ca53
4 changed files with 779 additions and 1 deletions

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defmodule Mix.Tasks.Bench.Sqlite do
@shortdoc "Benchmark SQLite concurrency against the running Phoenix stack"
@moduledoc """
Runs concurrent HTTP read and DB write benchmarks against the full
Phoenix stack to measure SQLite performance under realistic load.
Starts the server on port 4098, seeds temporary product data, runs
three scenarios at increasing concurrency, then cleans up.
## Usage
mix bench.sqlite
mix bench.sqlite --prod
## Options
* `--port PORT` - Port to start the server on (default: 4098)
* `--prod` - Re-run the benchmark compiled in prod mode (compiled
templates, no code reloader, no debug annotations). Automatically
sets `MIX_ENV=prod` and supplies the required env vars.
* `--pool-size N` - Override the DB connection pool size (default: 5).
Higher values allow more concurrent DB connections.
* `--scale N` - Multiply all concurrency levels by N (default: 1).
E.g. `--scale 4` runs 200/240/400/800 concurrent tasks.
* `--busy-timeout MS` - Override SQLite busy_timeout in milliseconds
(default: 5000). Higher values let writers wait longer for the lock.
"""
use Mix.Task
require Logger
@default_port 4098
@scenarios [
{"reads only", [readers: 50, writers: 0]},
{"mixed", [readers: 45, writers: 15]},
{"heavy mixed", [readers: 67, writers: 33]},
{"stress", [readers: 134, writers: 66]}
]
@impl Mix.Task
def run(args) do
{opts, _, _} =
OptionParser.parse(args,
strict: [
port: :integer,
prod: :boolean,
pool_size: :integer,
scale: :integer,
busy_timeout: :integer
]
)
bench_opts = %{
port: opts[:port] || @default_port,
pool_size: opts[:pool_size],
scale: opts[:scale] || 1,
busy_timeout: opts[:busy_timeout]
}
if opts[:prod] do
run_in_prod(bench_opts)
else
run_bench(bench_opts)
end
end
defp run_in_prod(%{port: port, pool_size: pool_size, scale: scale, busy_timeout: busy_timeout}) do
if Mix.env() == :prod do
run_bench(%{port: port, pool_size: pool_size, scale: scale, busy_timeout: busy_timeout})
else
Mix.shell().info("Re-launching in MIX_ENV=prod...")
db_path = Path.expand("berrypod_dev.db")
pool_env = if pool_size, do: "#{pool_size}", else: "5"
env = [
{"MIX_ENV", "prod"},
{"DATABASE_PATH", db_path},
{"SECRET_KEY_BASE", "bench_only_not_real_" <> String.duplicate("x", 44)},
{"PHX_HOST", "localhost"},
{"PORT", "#{port}"},
{"POOL_SIZE", pool_env}
]
args =
["bench.sqlite", "--port", "#{port}", "--scale", "#{scale}"] ++
if(pool_size, do: ["--pool-size", "#{pool_size}"], else: []) ++
if(busy_timeout, do: ["--busy-timeout", "#{busy_timeout}"], else: [])
System.cmd("mix", args,
env: env,
into: IO.stream(:stdio, :line),
stderr_to_stdout: true
)
end
end
defp run_bench(%{port: port, pool_size: pool_size, scale: scale, busy_timeout: busy_timeout}) do
base_url = start_server!(port)
# Apply repo overrides after app.start (runtime.exs runs during app.start
# and would overwrite anything we set before). Bounce the repo to pick up
# the new config.
if pool_size || busy_timeout do
repo_config = Application.get_env(:berrypod, Berrypod.Repo, [])
repo_config =
if pool_size, do: Keyword.put(repo_config, :pool_size, pool_size), else: repo_config
repo_config =
if busy_timeout,
do: Keyword.put(repo_config, :busy_timeout, busy_timeout),
else: repo_config
Application.put_env(:berrypod, Berrypod.Repo, repo_config)
Supervisor.terminate_child(Berrypod.Supervisor, Berrypod.Repo)
Supervisor.restart_child(Berrypod.Supervisor, Berrypod.Repo)
end
pause_oban!()
{conn, slugs} = seed_data!()
repo_conf = Application.get_env(:berrypod, Berrypod.Repo, [])
actual_pool = repo_conf[:pool_size] || 5
actual_bt = repo_conf[:busy_timeout] || 5000
mode = if Mix.env() == :prod, do: "prod", else: "dev"
try do
Mix.shell().info(
"\n--- SQLite bench (#{mode}, pool=#{actual_pool}, busy_timeout=#{actual_bt}ms, scale=#{scale}x) ---\n"
)
for {label, opts} <- @scenarios do
readers = opts[:readers] * scale
writers = opts[:writers] * scale
run_scenario(label, base_url, slugs, readers: readers, writers: writers)
end
after
resume_oban!()
cleanup!(conn)
end
end
# -- Server lifecycle --
defp start_server!(port) do
config = Application.get_env(:berrypod, BerrypodWeb.Endpoint, [])
config =
Keyword.merge(config,
http: [ip: {127, 0, 0, 1}, port: port],
server: true,
watchers: []
)
Application.put_env(:berrypod, BerrypodWeb.Endpoint, config)
Application.put_env(:logger, :level, :warning)
Mix.Task.run("app.start")
Logger.configure(level: :warning)
base_url = "http://localhost:#{port}"
wait_for_server(base_url, 20)
Mix.shell().info("Server started on #{base_url}")
base_url
end
defp wait_for_server(_url, 0) do
Mix.raise("Server failed to start")
end
defp wait_for_server(url, attempts) do
Application.ensure_all_started(:inets)
Application.ensure_all_started(:ssl)
case :httpc.request(:get, {~c"#{url}", []}, [timeout: 2_000], []) do
{:ok, {{_, status, _}, _, _}} when status in 200..399 ->
:ok
_ ->
Process.sleep(500)
wait_for_server(url, attempts - 1)
end
end
defp pause_oban! do
Oban.pause_all_queues(Oban)
Mix.shell().info("Oban queues paused for benchmark")
end
defp resume_oban! do
Oban.resume_all_queues(Oban)
Mix.shell().info("Oban queues resumed")
end
# -- Data seeding --
defp seed_data! do
alias Berrypod.{Products, Repo}
Mix.shell().info("Seeding bench data...")
{:ok, conn} =
Products.create_provider_connection(%{
provider_type: "printify",
name: "Bench Shop",
api_key: "bench_fake_key_12345",
config: %{"shop_id" => "99999"}
})
for i <- 1..20 do
{:ok, product, _} =
Products.upsert_product(conn, %{
provider_product_id: "bench-prov-#{i}",
title: "Bench Product #{i}",
description: "A benchmarking product, number #{i}."
})
for v <- 1..3 do
Products.create_product_variant(%{
product_id: product.id,
provider_variant_id: "bvar-#{i}-#{v}",
title: Enum.at(["S", "M", "L"], v - 1),
price: 1999 + v * 500,
is_enabled: true,
is_available: true
})
end
end
Berrypod.Search.rebuild_index()
%{rows: slug_rows} = Repo.query!("SELECT slug FROM products WHERE slug LIKE 'bench-%'")
slugs = List.flatten(slug_rows)
Mix.shell().info(" Seeded #{length(slugs)} products with variants")
{conn, slugs}
end
# -- Cleanup --
defp cleanup!(conn) do
alias Berrypod.{Products, Repo}
Mix.shell().info("\nCleaning up bench data...")
Repo.query!(
"DELETE FROM order_items WHERE order_id IN (SELECT id FROM orders WHERE customer_email LIKE 'bench_%')"
)
Repo.query!("DELETE FROM orders WHERE customer_email LIKE 'bench_%'")
Repo.query!(
"DELETE FROM product_variants WHERE product_id IN (SELECT id FROM products WHERE slug LIKE 'bench-%')"
)
Repo.query!(
"DELETE FROM product_images WHERE product_id IN (SELECT id FROM products WHERE slug LIKE 'bench-%')"
)
Repo.query!("DELETE FROM products WHERE slug LIKE 'bench-%'")
Products.delete_provider_connection(conn)
Berrypod.Search.rebuild_index()
Mix.shell().info(" Done.")
end
# -- Benchmark runner --
defp run_scenario(label, base_url, slugs, opts) do
readers = opts[:readers]
writers = opts[:writers]
total = readers + writers
read_urls = [base_url <> "/"] ++ Enum.map(slugs, &(base_url <> "/products/" <> &1))
# Interleave readers and writers for realistic ordering
task_types =
(List.duplicate(:read, readers) ++ List.duplicate(:write, writers))
|> Enum.shuffle()
{wall_time, results} =
:timer.tc(fn ->
task_types
|> Enum.with_index(1)
|> Enum.map(fn {type, i} ->
Task.async(fn -> run_task(type, i, read_urls) end)
end)
|> Task.await_many(120_000)
end)
print_results(label, total, readers, writers, wall_time, results)
end
defp run_task(:read, _i, read_urls) do
url = Enum.random(read_urls)
{time, result} =
:timer.tc(fn ->
try do
%{status: status} = Req.get!(url)
{:ok, status}
rescue
e -> {:error, Exception.message(e)}
end
end)
{time, :read, result}
end
defp run_task(:write, i, _read_urls) do
{time, result} =
:timer.tc(fn ->
try do
Berrypod.Orders.create_order(%{
customer_email: "bench_#{i}@example.com",
currency: "gbp",
items: [
%{
variant_id: "bench-var",
name: "Bench Item",
variant: "M",
price: 2499,
quantity: 1
}
]
})
rescue
e -> {:error, Exception.message(e)}
end
end)
{time, :write, result}
end
# -- Reporting --
defp print_results(label, total, readers, writers, wall_time, results) do
read_results = Enum.filter(results, fn {_, type, _} -> type == :read end)
write_results = Enum.filter(results, fn {_, type, _} -> type == :write end)
read_ok = Enum.count(read_results, fn {_, _, r} -> match?({:ok, 200}, r) end)
write_ok = Enum.count(write_results, fn {_, _, r} -> match?({:ok, _}, r) end)
write_err = length(write_results) - write_ok
read_lats = latencies(read_results)
write_lats = latencies(write_results)
Mix.shell().info("""
#{label} (#{total} concurrent: #{readers} reads + #{writers} writes)
wall time: #{div(wall_time, 1000)}ms
reads: #{read_ok}/#{length(read_results)} ok#{format_latencies(read_lats)}
writes: #{write_ok}/#{length(write_results)} ok, #{write_err} errors#{format_latencies(write_lats)}
""")
end
defp latencies([]), do: []
defp latencies(results) do
results
|> Enum.map(fn {us, _, _} -> div(us, 1000) end)
|> Enum.sort()
end
defp format_latencies([]), do: ""
defp format_latencies(sorted) do
n = length(sorted)
p50 = Enum.at(sorted, div(n, 2))
p95 = Enum.at(sorted, round(n * 0.95) - 1)
"\n p50: #{p50}ms p95: #{p95}ms max: #{List.last(sorted)}ms"
end
end

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defmodule Berrypod.SQLiteConcurrencyTest do
@moduledoc """
Tests and benchmarks for SQLite concurrent read/write behaviour.
Correctness tests run as part of the normal suite. Benchmark tests are
tagged :benchmark and excluded by default run them with:
mix test test/berrypod/sqlite_concurrency_test.exs --include benchmark
"""
use ExUnit.Case, async: false
@tmp_dir System.tmp_dir!()
# -------------------------------------------------------------------
# Helpers
# -------------------------------------------------------------------
defp start_bench_repo(opts) do
db_path = Path.join(@tmp_dir, "bench_#{System.unique_integer([:positive])}.db")
defaults = [
database: db_path,
pool_size: 5,
journal_mode: :wal,
busy_timeout: 5000
]
config = Keyword.merge(defaults, opts)
{:ok, pid} = Berrypod.BenchRepo.start_link(config)
Berrypod.BenchRepo.query!("""
CREATE TABLE bench (
id INTEGER PRIMARY KEY AUTOINCREMENT,
value TEXT NOT NULL,
payload TEXT DEFAULT ''
)
""")
{pid, db_path}
end
defp stop_bench_repo(pid, db_path) do
GenServer.stop(pid)
File.rm(db_path)
File.rm(db_path <> "-wal")
File.rm(db_path <> "-shm")
end
defp seed_rows(n) do
for i <- 1..n do
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value, payload) VALUES (?, ?)",
["row_#{i}", String.duplicate("x", 200)]
)
end
end
defp run_concurrent(n, fun) do
tasks =
for i <- 1..n do
Task.async(fn ->
{time_us, result} = :timer.tc(fn -> fun.(i) end)
{time_us, result}
end)
end
Task.await_many(tasks, 30_000)
end
defp count_rows do
%{rows: [[count]]} = Berrypod.BenchRepo.query!("SELECT COUNT(*) FROM bench")
count
end
# -------------------------------------------------------------------
# Correctness tests (always run)
# -------------------------------------------------------------------
describe "pragma configuration" do
test "PRAGMAs are applied correctly on connection" do
{pid, db_path} =
start_bench_repo(
journal_mode: :wal,
cache_size: -20_000,
journal_size_limit: 67_108_864,
custom_pragmas: [mmap_size: 134_217_728]
)
assert_pragma("journal_mode", "wal")
assert_pragma("synchronous", 1)
assert_pragma("foreign_keys", 1)
assert_pragma("temp_store", 2)
assert_pragma("cache_size", -20_000)
assert_pragma("mmap_size", 134_217_728)
assert_pragma("journal_size_limit", 67_108_864)
# busy_timeout isn't queryable via PRAGMA in all SQLite builds,
# but we can verify it was accepted by the absence of errors above
stop_bench_repo(pid, db_path)
end
end
describe "concurrent reads" do
test "multiple readers don't block each other under WAL" do
{pid, db_path} = start_bench_repo(pool_size: 5)
seed_rows(500)
results =
run_concurrent(20, fn _i ->
%{rows: rows} =
Berrypod.BenchRepo.query!("SELECT * FROM bench WHERE value LIKE '%_5%'")
{:ok, length(rows)}
end)
# All 20 should succeed
outcomes = Enum.map(results, fn {_us, result} -> result end)
assert Enum.all?(outcomes, &match?({:ok, _}, &1))
# All should find the same number of matching rows
counts = Enum.map(outcomes, fn {:ok, n} -> n end)
assert length(Enum.uniq(counts)) == 1
stop_bench_repo(pid, db_path)
end
end
describe "concurrent writes" do
test "bare inserts all succeed with busy_timeout" do
{pid, db_path} = start_bench_repo(pool_size: 5, busy_timeout: 5000)
results =
run_concurrent(20, fn i ->
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value) VALUES (?)",
["writer_#{i}"]
)
:ok
end)
outcomes = Enum.map(results, fn {_us, result} -> result end)
assert Enum.all?(outcomes, &(&1 == :ok))
assert count_rows() == 20
stop_bench_repo(pid, db_path)
end
test "transactions succeed with IMMEDIATE mode" do
{pid, db_path} =
start_bench_repo(
pool_size: 5,
busy_timeout: 5000,
default_transaction_mode: :immediate
)
results =
run_concurrent(20, fn i ->
Berrypod.BenchRepo.transaction(fn ->
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value) VALUES (?)",
["tx_writer_#{i}"]
)
end)
end)
outcomes = Enum.map(results, fn {_us, result} -> result end)
assert Enum.all?(outcomes, &match?({:ok, _}, &1))
assert count_rows() == 20
stop_bench_repo(pid, db_path)
end
end
describe "transaction upgrade behaviour" do
test "DEFERRED mode may fail when upgrading read to write" do
# This test demonstrates the transaction upgrade problem.
# Under DEFERRED, a transaction that starts with a read and then
# tries to write can get SQLITE_BUSY if another writer holds the lock.
# It's timing-dependent so we run many attempts to increase the chance.
{pid, db_path} = start_bench_repo(pool_size: 5, busy_timeout: 50)
seed_rows(100)
results =
run_concurrent(30, fn i ->
try do
Berrypod.BenchRepo.transaction(fn ->
# Start with a read (deferred transaction stays as reader)
Berrypod.BenchRepo.query!("SELECT * FROM bench WHERE id = ?", [rem(i, 100) + 1])
# Small delay to increase contention window
Process.sleep(1)
# Now try to write (requires upgrade from reader to writer)
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value) VALUES (?)",
["upgrade_#{i}"]
)
end)
rescue
e -> {:error, e}
end
end)
errors =
Enum.count(results, fn
{_us, {:error, _}} -> true
_ -> false
end)
# We can't guarantee failures (timing-dependent), but log what happened
successes = 30 - errors
IO.puts("\n DEFERRED upgrade: #{successes}/30 succeeded, #{errors}/30 failed")
stop_bench_repo(pid, db_path)
end
test "IMMEDIATE mode prevents transaction upgrade failures" do
{pid, db_path} =
start_bench_repo(
pool_size: 5,
busy_timeout: 5000,
default_transaction_mode: :immediate
)
seed_rows(100)
results =
run_concurrent(30, fn i ->
Berrypod.BenchRepo.transaction(fn ->
# Read then write — no upgrade problem because lock taken upfront
Berrypod.BenchRepo.query!("SELECT * FROM bench WHERE id = ?", [rem(i, 100) + 1])
Process.sleep(1)
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value) VALUES (?)",
["immediate_#{i}"]
)
end)
end)
outcomes = Enum.map(results, fn {_us, result} -> result end)
successes = Enum.count(outcomes, &match?({:ok, _}, &1))
errors =
Enum.count(outcomes, fn
{:error, _} -> true
_ -> false
end)
IO.puts("\n IMMEDIATE mode: #{successes}/30 succeeded, #{errors}/30 failed")
assert errors == 0, "IMMEDIATE mode should prevent all upgrade failures"
stop_bench_repo(pid, db_path)
end
end
# -------------------------------------------------------------------
# Benchmarks (tagged, skipped by default)
# -------------------------------------------------------------------
describe "benchmark: read throughput vs pool size" do
@describetag :benchmark
test "concurrent reads scale with pool size" do
# Pool size 1 — all reads serialized
{pid1, path1} = start_bench_repo(pool_size: 1)
seed_rows(5000)
{time_pool1, _} =
:timer.tc(fn ->
run_concurrent(50, fn _i ->
Berrypod.BenchRepo.query!("SELECT * FROM bench WHERE value LIKE '%_42%'")
end)
end)
stop_bench_repo(pid1, path1)
# Pool size 5 — reads can run concurrently under WAL
{pid5, path5} = start_bench_repo(pool_size: 5)
seed_rows(5000)
{time_pool5, _} =
:timer.tc(fn ->
run_concurrent(50, fn _i ->
Berrypod.BenchRepo.query!("SELECT * FROM bench WHERE value LIKE '%_42%'")
end)
end)
stop_bench_repo(pid5, path5)
IO.puts("""
\n Read throughput (50 concurrent reads, 5000 rows):
pool_size=1: #{div(time_pool1, 1000)}ms
pool_size=5: #{div(time_pool5, 1000)}ms
speedup: #{Float.round(time_pool1 / max(time_pool5, 1), 2)}x
""")
assert time_pool5 < time_pool1,
"Pool size 5 should be faster than 1 for concurrent reads"
end
end
describe "benchmark: write throughput vs pool size" do
@describetag :benchmark
test "concurrent writes with different pool sizes" do
for pool_size <- [1, 3, 5] do
{pid, db_path} =
start_bench_repo(
pool_size: pool_size,
busy_timeout: 5000,
default_transaction_mode: :immediate
)
{time_us, results} =
:timer.tc(fn ->
run_concurrent(100, fn i ->
Berrypod.BenchRepo.query!(
"INSERT INTO bench (value) VALUES (?)",
["pool#{pool_size}_#{i}"]
)
:ok
end)
end)
successes = Enum.count(results, fn {_us, r} -> r == :ok end)
rows = count_rows()
IO.puts(
" pool_size=#{pool_size}: #{div(time_us, 1000)}ms, " <>
"#{successes}/100 succeeded, #{rows} rows"
)
stop_bench_repo(pid, db_path)
end
end
end
describe "benchmark: mmap_size impact" do
@describetag :benchmark
test "read performance with and without mmap" do
# Without mmap
{pid0, path0} = start_bench_repo(pool_size: 5, custom_pragmas: [mmap_size: 0])
seed_rows(10_000)
{time_no_mmap, _} =
:timer.tc(fn ->
run_concurrent(30, fn _i ->
Berrypod.BenchRepo.query!("SELECT COUNT(*), AVG(length(payload)) FROM bench")
end)
end)
stop_bench_repo(pid0, path0)
# With 128MB mmap
{pid128, path128} =
start_bench_repo(pool_size: 5, custom_pragmas: [mmap_size: 134_217_728])
seed_rows(10_000)
{time_mmap, _} =
:timer.tc(fn ->
run_concurrent(30, fn _i ->
Berrypod.BenchRepo.query!("SELECT COUNT(*), AVG(length(payload)) FROM bench")
end)
end)
stop_bench_repo(pid128, path128)
IO.puts("""
\n mmap impact (30 concurrent reads, 10000 rows):
mmap_size=0: #{div(time_no_mmap, 1000)}ms
mmap_size=128M: #{div(time_mmap, 1000)}ms
speedup: #{Float.round(time_no_mmap / max(time_mmap, 1), 2)}x
""")
end
end
# -------------------------------------------------------------------
# Private
# -------------------------------------------------------------------
defp assert_pragma(name, expected) do
%{rows: [[value]]} = Berrypod.BenchRepo.query!("PRAGMA #{name}")
assert value == expected, "PRAGMA #{name}: expected #{expected}, got #{value}"
end
end

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defmodule Berrypod.BenchRepo do
@moduledoc """
Standalone Ecto Repo for SQLite concurrency tests.
Started dynamically against temp DB files no Sandbox, no Application
config dependency. Each test controls pool size, PRAGMAs, and transaction
mode independently.
"""
use Ecto.Repo,
otp_app: :berrypod,
adapter: Ecto.Adapters.SQLite3
end

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ExUnit.start()
ExUnit.start(exclude: [:benchmark])
Ecto.Adapters.SQL.Sandbox.mode(Berrypod.Repo, :manual)