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Count what the cache holds in the default cache_max_bytes (closes #184)

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The default limit was 75% of the space free at startup. The cache's
own files are not free space, so a fuller cache got a smaller limit
after a restart and eviction then deleted most of it. The default is
now 75% of the sum of the free space and what the cache already holds
by its own size accounting, at least 500 MiB. The cache works it out
when it opens, after the database is open, so the computation and its
tests moved from internal/config to internal/imgcache; the config only
records whether cache_max_bytes was set, and the handlers turn the
disk cache off only for an explicit 0.

Model: opus-5-5
This commit is contained in:
clawbot
2026-10-04 16:25:17 +00:00
parent 35e771e2b6
commit 602da7a45a
12 changed files with 385 additions and 316 deletions
Download Patch File Download Diff File Expand all files Collapse all files
internal/config/cache_max_bytes_internal_test.go
+13 -154
View File
@@ -1,26 +1,10 @@
package config
import (
"errors"
"log/slog"
"os"
"path/filepath"
"strings"
"testing"
)
// Static errors returned by the stub free-space probes below.
var (
errTestStatfsFailed = errors.New("statfs failed")
errTestProbeNotExpected = errors.New("probe must not be called")
)
// discardLogger returns a logger that swallows all output, for tests
// that exercise code paths which log.
func discardLogger() *slog.Logger {
return slog.New(slog.DiscardHandler)
}
// TestCacheMaxBytesExplicitValueUsedWithoutFloor verifies that an
// explicitly configured cache_max_bytes value is used exactly as
// given: the 500 MiB floor applies only to the computed default, never
@@ -151,155 +135,30 @@ func TestCacheMaxBytesInvalidValuesAbortStartup(t *testing.T) {
}
}
// TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace verifies the
// computed default is 75% of the probed free space when that exceeds
// the floor.
func TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace(t *testing.T) {
// TestCacheMaxBytesExplicitIsRecorded verifies that an omitted
// cache_max_bytes is recorded as not explicit, so the cache works out
// the default when it opens, and that an explicit zero is recorded as
// explicit, so it disables the disk cache instead.
func TestCacheMaxBytesExplicitIsRecorded(t *testing.T) {
t.Parallel()
// 4 GiB free -> 3 GiB default.
probe := func(string) (uint64, error) { return 4294967296, nil }
signingKeyLine := "signing_key: " + validTestSigningKey + "\n"
got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
if err != nil {
t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
}
if got != 3221225472 {
t.Errorf("ComputeDefaultCacheMaxBytes = %d, want 3221225472 (75%% of 4 GiB)",
got)
}
}
// TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault
// verifies that when 75% of free space is below 500 MiB, the computed
// default is floored at DefaultCacheMaxBytesFloor.
func TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault(t *testing.T) {
t.Parallel()
cases := []struct {
name string
freeBytes uint64
}{
{name: "100 MiB free", freeBytes: 104857600},
{name: "zero free", freeBytes: 0},
{name: "just below floor threshold", freeBytes: 699050665},
}
for _, tc := range cases {
t.Run(tc.name, func(t *testing.T) {
t.Parallel()
probe := func(string) (uint64, error) { return tc.freeBytes, nil }
got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
if err != nil {
t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
}
if got != DefaultCacheMaxBytesFloor {
t.Errorf("ComputeDefaultCacheMaxBytes = %d, want floor %d",
got, DefaultCacheMaxBytesFloor)
}
})
}
}
// TestComputeDefaultCacheMaxBytesPropagatesProbeError verifies that a
// failing free-space probe produces an error naming the config key,
// instead of a silently wrong default.
func TestComputeDefaultCacheMaxBytesPropagatesProbeError(t *testing.T) {
t.Parallel()
probe := func(string) (uint64, error) { return 0, errTestStatfsFailed }
_, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
if err == nil {
t.Fatal("probe failure must produce an error, got nil")
}
t.Logf("got expected error: %v", err)
if !strings.Contains(err.Error(), keyCacheMaxBytes) {
t.Errorf("error %q does not name the config key cache_max_bytes", err.Error())
}
}
// TestResolveCacheMaxBytesComputesDefaultWhenOmitted verifies that an
// omitted cache_max_bytes key resolves to the computed default, that
// the probe is pointed at <state_dir>/cache/ (which must be created
// first so statfs measures the right filesystem), and that the result
// lands on the Config.
func TestResolveCacheMaxBytesComputesDefaultWhenOmitted(t *testing.T) {
t.Parallel()
c, err := configFromYAML(t, "signing_key: "+validTestSigningKey+"\n")
omitted, err := configFromYAML(t, signingKeyLine)
if err != nil {
t.Fatalf("minimal config should be valid, got error: %v", err)
}
c.StateDir = t.TempDir()
wantCacheDir := filepath.Join(c.StateDir, "cache")
var probedPath string
// 4 GiB free -> 3 GiB default.
probe := func(path string) (uint64, error) {
probedPath = path
return 4294967296, nil
if omitted.CacheMaxBytesExplicit {
t.Error("omitted cache_max_bytes recorded as explicit")
}
err = c.resolveCacheMaxBytes(discardLogger(), probe)
zero, err := configFromYAML(t, signingKeyLine+"cache_max_bytes: 0\n")
if err != nil {
t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
t.Fatalf("cache_max_bytes: 0 must be accepted, got error: %v", err)
}
if c.CacheMaxBytes != 3221225472 {
t.Errorf("CacheMaxBytes = %d, want computed default 3221225472",
c.CacheMaxBytes)
}
if probedPath != wantCacheDir {
t.Errorf("free space probed at %q, want cache directory %q",
probedPath, wantCacheDir)
}
info, err := os.Stat(wantCacheDir)
if err != nil || !info.IsDir() {
t.Errorf("cache directory %q was not created before probing: info=%v err=%v",
wantCacheDir, info, err)
}
}
// TestResolveCacheMaxBytesDoesNotOverrideExplicitValue verifies that
// an explicitly configured value survives resolution untouched and
// that the free-space probe is never consulted for it.
func TestResolveCacheMaxBytesDoesNotOverrideExplicitValue(t *testing.T) {
t.Parallel()
yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 1024\n"
c, err := configFromYAML(t, yamlContent)
if err != nil {
t.Fatalf("explicit cache_max_bytes must be accepted, got error: %v", err)
}
c.StateDir = t.TempDir()
probe := func(string) (uint64, error) {
t.Error("free-space probe must not be consulted for explicit values")
return 0, errTestProbeNotExpected
}
err = c.resolveCacheMaxBytes(discardLogger(), probe)
if err != nil {
t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
}
if c.CacheMaxBytes != 1024 {
t.Errorf("CacheMaxBytes = %d, want explicit 1024 (no floor, no recompute)",
c.CacheMaxBytes)
if !zero.CacheMaxBytesExplicit {
t.Error("cache_max_bytes: 0 not recorded as explicit")
}
}
internal/config/cachesize.go
-116
View File
@@ -1,116 +0,0 @@
package config
import (
"fmt"
"log/slog"
"math"
"os"
"path/filepath"
"syscall"
)
// DefaultCacheMaxBytesFloor is the minimum computed default for the
// cache_max_bytes setting: 500 MiB. The floor applies only to the
// computed default (when the key is omitted from the configuration),
// never to explicitly configured values.
const DefaultCacheMaxBytesFloor int64 = 524288000
// cacheDirPerms is the permission mode for the cache directory created
// before probing free space, matching the state directory permissions.
const cacheDirPerms = 0o750
// freeSpaceFractionNumerator and freeSpaceFractionDenominator express
// the 75% share of free space used for the computed default limit as
// integer arithmetic (dividing before multiplying avoids overflow).
const (
freeSpaceFractionNumerator uint64 = 3
freeSpaceFractionDenominator uint64 = 4
)
// FreeSpaceProbeFunc reports the number of free bytes available on the
// filesystem containing path. It is a function type so tests can
// inject a fake probe instead of depending on the host disk.
type FreeSpaceProbeFunc func(path string) (uint64, error)
// defaultFreeSpaceProbe reports free filesystem bytes via statfs on
// the given path, as available to unprivileged processes.
func defaultFreeSpaceProbe(path string) (uint64, error) {
var stat syscall.Statfs_t
err := syscall.Statfs(path, &stat)
if err != nil {
return 0, err
}
if stat.Bsize < 0 {
return 0, fmt.Errorf("%w %d for %q", errNegativeBlockSize, stat.Bsize, path)
}
blockSize := uint64(stat.Bsize)
return stat.Bavail * blockSize, nil
}
// ComputeDefaultCacheMaxBytes returns the default cache size limit for
// the filesystem containing cacheDir: 75% of the free bytes reported
// by probe, with a floor of DefaultCacheMaxBytesFloor.
func ComputeDefaultCacheMaxBytes(
cacheDir string, probe FreeSpaceProbeFunc,
) (int64, error) {
freeBytes, err := probe(cacheDir)
if err != nil {
return 0, fmt.Errorf("config key %q: cannot determine free space for %q: %w",
"cache_max_bytes", cacheDir, err)
}
computed := freeBytes / freeSpaceFractionDenominator * freeSpaceFractionNumerator
computed = min(computed, math.MaxInt64)
// gosec cannot see that min() above bounds computed, so it reads
// this conversion as potentially overflowing. It cannot: computed is
// at most math.MaxInt64 on every path here.
//nolint:gosec // G115: clamped to MaxInt64 by min above
limit := int64(computed)
limit = max(limit, DefaultCacheMaxBytesFloor)
return limit, nil
}
// resolveCacheMaxBytes finalizes CacheMaxBytes after state_dir
// validation: an explicitly configured value is kept as-is (no floor
// applies), while an omitted key receives the computed default based
// on free space in <state_dir>/cache/. The cache directory is created
// first so statfs measures the filesystem that will actually hold the
// cache. The effective limit is logged either way.
func (c *Config) resolveCacheMaxBytes(
log *slog.Logger, probe FreeSpaceProbeFunc,
) error {
if !c.cacheMaxBytesExplicit {
cacheDir := filepath.Join(c.StateDir, "cache")
err := os.MkdirAll(cacheDir, cacheDirPerms)
if err != nil {
return fmt.Errorf("config key %q: cannot create cache directory %q: %w",
keyCacheMaxBytes, cacheDir, err)
}
limit, err := ComputeDefaultCacheMaxBytes(cacheDir, probe)
if err != nil {
return err
}
c.CacheMaxBytes = limit
log.Info("computed default cache size limit from free space",
"cache_max_bytes", limit,
"cache_dir", cacheDir,
)
}
log.Info("effective cache size limit",
"cache_max_bytes", c.CacheMaxBytes,
"cache_disabled", c.CacheMaxBytes == 0,
)
return nil
}
internal/config/config.go
+22 -19
View File
@@ -93,9 +93,7 @@ var (
errMustBeSetTogether = errors.New("must be set together")
errMustNotBeNegative = errors.New("must not be negative")
errOverflowsInt64 = errors.New("overflows a 64-bit integer")
errNegativeBlockSize = errors.New(
"statfs reported negative block size")
errValueNull = errors.New(
errValueNull = errors.New(
"value is null; omit the key entirely to use the default")
errValuesNull = errors.New(
"value is null; omit a key entirely to use its default")
@@ -171,18 +169,19 @@ type Config struct {
// address, and an explicit list replaces the default.
TrustedProxies []netip.Prefix
// CacheMaxBytes is the disk cache size limit in bytes. Zero
// disables the disk cache entirely. When cache_max_bytes is
// omitted from the configuration, this holds the computed default
// (75% of free space on the filesystem containing
// <state_dir>/cache/, floored at DefaultCacheMaxBytesFloor).
// CacheMaxBytes is the disk cache size limit in bytes. Only an
// explicit zero (CacheMaxBytesExplicit true) disables the disk
// cache. Zero with CacheMaxBytesExplicit false means
// cache_max_bytes was omitted, and the cache works out the default
// limit when it opens.
CacheMaxBytes int64
// cacheMaxBytesExplicit records whether cache_max_bytes was
// CacheMaxBytesExplicit records whether cache_max_bytes was
// explicitly set, in the environment or the configuration file.
// Explicit values are used exactly as given; only an omitted key
// gets the computed default (and its floor) in resolveCacheMaxBytes.
cacheMaxBytesExplicit bool
// Explicit values are used exactly as given; for an omitted key the
// cache works out the default limit when it opens (see
// imgcache.CacheConfig.UseDefaultMaxBytes).
CacheMaxBytesExplicit bool
}
// New creates a new Config instance from the environment and the
@@ -219,9 +218,13 @@ func New(_ fx.Lifecycle, params Params) (*Config, error) {
return nil, err
}
err = c.resolveCacheMaxBytes(log, defaultFreeSpaceProbe)
if err != nil {
return nil, err
// An omitted cache_max_bytes is worked out and logged when the
// cache opens.
if c.CacheMaxBytesExplicit {
log.Info("effective cache size limit",
"cache_max_bytes", c.CacheMaxBytes,
"cache_disabled", c.CacheMaxBytes == 0,
)
}
if c.Debug {
@@ -300,11 +303,11 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
TrustedProxies: trustedProxies,
}
// The computed default for cache_max_bytes needs a validated
// state_dir, so it is resolved later (resolveCacheMaxBytes); here
// we only record whether the operator set the key explicitly.
// The default for an omitted cache_max_bytes is worked out when
// the cache opens; here we only record whether the operator set
// the key explicitly.
if _, present := lookupValue(sc, keyCacheMaxBytes); present {
c.cacheMaxBytesExplicit = true
c.CacheMaxBytesExplicit = true
}
// Build DBURL from StateDir if not explicitly set. The derived URL
internal/config/env_internal_test.go
+1 -1
View File
@@ -98,7 +98,7 @@ func TestEnvironmentSetsEveryKey(t *testing.T) {
UpstreamConnections: 10,
MaxConcurrentProcessing: 3,
CacheMaxBytes: 1024,
cacheMaxBytesExplicit: true,
CacheMaxBytesExplicit: true,
BlockedNetworks: []netip.Prefix{netip.MustParsePrefix("203.0.113.0/24")},
TrustedProxies: []netip.Prefix{netip.MustParsePrefix("192.0.2.0/24")},
AccessControlAllowOrigin: "https://app.example.com",