perf(s3): add optional shared in-memory chunk cache for GET (#9069)

Adds the -s3.cacheCapacityMB flag (default 0, disabled) that attaches
an in-memory chunk_cache.ChunkCacheInMemory to the server-wide
ReaderCache introduced in the previous commit. When enabled,
completed chunks are deposited into the shared cache as they are
downloaded, so concurrent and repeat GETs of the same object hit
memory instead of re-fetching chunks from volume servers.

When 0 (the default) the shared ReaderCache still runs — it just
attaches a nil chunk cache, so behaviour matches the previous commit
exactly. No behaviour change for clusters that don't opt in.

Disk-backed TieredChunkCache was evaluated and rejected: its
synchronous SetChunk writes regressed cold reads ~12x on loopback
because the chunk fetchers block on local disk I/O that is *slower*
than the TCP volume-server fetch it is supposed to accelerate.
Memory-only avoids that.

Flag registered in all four S3 flag sites (s3.go, server.go,
filer.go, mini.go) per the comment on command.S3Options. The chunk
size used to convert CacheSizeMB → entry count is encapsulated in
the s3ChunkCacheChunkSizeMB constant so it's easy to grep and
revisit if the filer default chunk size changes.

Measured on weed mini + 1 GiB random object over loopback, single
curl on a presigned URL:

    cacheCapacityMB=0 (off):  cold ~2900, warm ~2900 MB/s
    cacheCapacityMB=4096:     cold ~2790, warm ~5050 MB/s (+70%)

weed/command/filer.go

@@ -150,6 +150,7 @@ func init() {
 	filerS3Options.portIceberg = cmdFiler.Flag.Int("s3.port.iceberg", 8181, "Iceberg REST Catalog server listen port (0 to disable)")
 	filerS3Options.externalUrl = cmdFiler.Flag.String("s3.externalUrl", "", "the external URL clients use to connect (e.g. https://api.example.com:9000). Used for S3 signature verification behind a reverse proxy. Falls back to S3_EXTERNAL_URL env var.")
 	filerS3Options.defaultFileMode = cmdFiler.Flag.String("s3.defaultFileMode", "", "default file mode for S3 uploaded objects, e.g. 0660, 0644, 0666")
+	filerS3Options.cacheSizeMB = cmdFiler.Flag.Int64("s3.cacheCapacityMB", 0, "in-memory chunk cache capacity in MB for S3 GETs shared across requests (0 disables)")
 
 	// start webdav on filer
 	filerStartWebDav = cmdFiler.Flag.Bool("webdav", false, "whether to start webdav gateway")

weed/command/mini.go

@@ -251,6 +251,7 @@ func initMiniS3Flags() {
 	miniS3Options.allowDeleteBucketNotEmpty = miniS3AllowDeleteBucketNotEmpty
 	miniS3Options.externalUrl = cmdMini.Flag.String("s3.externalUrl", "", "the external URL clients use to connect (e.g. https://api.example.com:9000). Used for S3 signature verification behind a reverse proxy. Falls back to S3_EXTERNAL_URL env var.")
 	miniS3Options.defaultFileMode = cmdMini.Flag.String("s3.defaultFileMode", "", "default file mode for S3 uploaded objects, e.g. 0660, 0644, 0666")
+	miniS3Options.cacheSizeMB = cmdMini.Flag.Int64("s3.cacheCapacityMB", 0, "in-memory chunk cache capacity in MB for S3 GETs shared across requests (0 disables)")
 	// In mini mode, S3 uses the shared debug server started at line 681, not its own separate debug server
 	miniS3Options.debug = new(bool) // explicitly false
 	miniS3Options.debugPort = cmdMini.Flag.Int("s3.debug.port", 6060, "http port for debugging (unused in mini mode)")

weed/command/s3.go

@@ -73,6 +73,7 @@ type S3Options struct {
 	cipher                    *bool
 	externalUrl               *string
 	defaultFileMode           *string
+	cacheSizeMB               *int64
 }
 
 func init() {
@@ -109,6 +110,7 @@ func init() {
 	s3StandaloneOptions.cipher = cmdS3.Flag.Bool("encryptVolumeData", false, "encrypt data on volume servers")
 	s3StandaloneOptions.externalUrl = cmdS3.Flag.String("externalUrl", "", "the external URL clients use to connect (e.g. https://api.example.com:9000). Used for S3 signature verification behind a reverse proxy. Falls back to S3_EXTERNAL_URL env var.")
 	s3StandaloneOptions.defaultFileMode = cmdS3.Flag.String("defaultFileMode", "", "default file mode for S3 uploaded objects, e.g. 0660, 0644, 0666")
+	s3StandaloneOptions.cacheSizeMB = cmdS3.Flag.Int64("cacheCapacityMB", 0, "in-memory chunk cache capacity in MB for S3 GETs shared across requests (0 disables)")
 }
 
 var cmdS3 = &Command{
@@ -343,6 +345,7 @@ func (s3opt *S3Options) startS3Server() bool {
 		GrpcPort:                  *s3opt.portGrpc,
 		ExternalUrl:               s3opt.resolveExternalUrl(),
 		DefaultFileMode:           defaultFileMode,
+		CacheSizeMB:               *s3opt.cacheSizeMB,
 	})
 	if s3ApiServer_err != nil {
 		glog.Fatalf("S3 API Server startup error: %v", s3ApiServer_err)

weed/command/server.go

@@ -181,6 +181,7 @@ func init() {
 	s3Options.cipher = cmdServer.Flag.Bool("s3.encryptVolumeData", false, "encrypt data on volume servers for S3 uploads")
 	s3Options.externalUrl = cmdServer.Flag.String("s3.externalUrl", "", "the external URL clients use to connect (e.g. https://api.example.com:9000). Used for S3 signature verification behind a reverse proxy. Falls back to S3_EXTERNAL_URL env var.")
 	s3Options.defaultFileMode = cmdServer.Flag.String("s3.defaultFileMode", "", "default file mode for S3 uploaded objects, e.g. 0660, 0644, 0666")
+	s3Options.cacheSizeMB = cmdServer.Flag.Int64("s3.cacheCapacityMB", 0, "in-memory chunk cache capacity in MB for S3 GETs shared across requests (0 disables)")
 
 	sftpOptions.port = cmdServer.Flag.Int("sftp.port", 2022, "SFTP server listen port")
 	sftpOptions.sshPrivateKey = cmdServer.Flag.String("sftp.sshPrivateKey", "", "path to the SSH private key file for host authentication")