Shrink default LRU cache sizes.

Observing Prometheus in production confirms we can lower these values
safely.

storage/metric/leveldb.go

@@ -49,13 +49,13 @@ var (
 
 	// These flag values are back of the envelope, though they seem sensible.
 	// Please re-evaluate based on your own needs.
-	curationRemarksCacheSize         = flag.Int("curationRemarksCacheSize", 50*1024*1024, "The size for the curation remarks cache (bytes).")
-	fingerprintsToLabelPairCacheSize = flag.Int("fingerprintsToLabelPairCacheSizeBytes", 100*1024*1024, "The size for the fingerprint to label pair index (bytes).")
-	highWatermarkCacheSize           = flag.Int("highWatermarksByFingerprintSizeBytes", 50*1024*1024, "The size for the metric high watermarks (bytes).")
-	labelNameToFingerprintsCacheSize = flag.Int("labelNameToFingerprintsCacheSizeBytes", 100*1024*1024, "The size for the label name to metric fingerprint index (bytes).")
-	labelPairToFingerprintsCacheSize = flag.Int("labelPairToFingerprintsCacheSizeBytes", 100*1024*1024, "The size for the label pair to metric fingerprint index (bytes).")
-	metricMembershipIndexCacheSize   = flag.Int("metricMembershipCacheSizeBytes", 50*1024*1024, "The size for the metric membership index (bytes).")
-	samplesByFingerprintCacheSize    = flag.Int("samplesByFingerprintCacheSizeBytes", 500*1024*1024, "The size for the samples database (bytes).")
+	curationRemarksCacheSize         = flag.Int("curationRemarksCacheSize", 5*1024*1024, "The size for the curation remarks cache (bytes).")
+	fingerprintsToLabelPairCacheSize = flag.Int("fingerprintsToLabelPairCacheSizeBytes", 25*1024*1024, "The size for the fingerprint to label pair index (bytes).")
+	highWatermarkCacheSize           = flag.Int("highWatermarksByFingerprintSizeBytes", 5*1024*1024, "The size for the metric high watermarks (bytes).")
+	labelNameToFingerprintsCacheSize = flag.Int("labelNameToFingerprintsCacheSizeBytes", 25*1024*1024, "The size for the label name to metric fingerprint index (bytes).")
+	labelPairToFingerprintsCacheSize = flag.Int("labelPairToFingerprintsCacheSizeBytes", 25*1024*1024, "The size for the label pair to metric fingerprint index (bytes).")
+	metricMembershipIndexCacheSize   = flag.Int("metricMembershipCacheSizeBytes", 5*1024*1024, "The size for the metric membership index (bytes).")
+	samplesByFingerprintCacheSize    = flag.Int("samplesByFingerprintCacheSizeBytes", 50*1024*1024, "The size for the samples database (bytes).")
 )
 
 type leveldbOpener func()