colblk: improve Uint encoding for very few rows

We currently choose the best uint encoding assuming we have a decent number of rows. For less than 8 rows, the best encoding might be different: e.g. a non-delta encoding with 2 bytes per row can be smaller than an 8 byte delta base plus 1 byte per row. In rare cases, this can make blocks *decrease* in size when we add a row which can be confusing (especially in tests). This change takes the number of rows into account to get the smallest possible encoding.
cockroachdb · Oct 15, 2024 · 88babd7 · 88babd7
1 parent fbbf740
commit 88babd7
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Showing 11 changed files with 707 additions and 563 deletions.
diff --git a/sstable/colblk/prefix_bytes.go b/sstable/colblk/prefix_bytes.go
@@ -822,7 +822,7 @@ func (b *PrefixBytesBuilder) Put(key []byte, bytesSharedWithPrev int) {
 			currentBundlePrefixOffset: 1,
 			completedBundleLen:        0,
 			compressedDataLen:         len(key),
-			offsetEncoding:            DetermineUintEncoding(0, uint64(len(key))),
+			offsetEncoding:            DetermineUintEncoding(0, uint64(len(key)), UintEncodingRowThreshold),
 		}
 	case b.nKeys&(b.bundleSize-1) == 0:
 		// We're starting a new bundle.
@@ -855,7 +855,7 @@ func (b *PrefixBytesBuilder) Put(key []byte, bytesSharedWithPrev int) {
 			currentBundleDistinctKeys: 1,
 			compressedDataLen:         completedBundleSize + len(key) - (b.bundleCount(b.nKeys)-1)*blockPrefixLen,
 		}
-		curr.offsetEncoding = DetermineUintEncoding(0, uint64(curr.compressedDataLen))
+		curr.offsetEncoding = DetermineUintEncoding(0, uint64(curr.compressedDataLen), UintEncodingRowThreshold)
 		b.data = append(b.data, key...)
 		b.addOffset(0) // Placeholder for bundle prefix.
 		b.addOffset(uint32(len(b.data)))
@@ -897,7 +897,7 @@ func (b *PrefixBytesBuilder) Put(key []byte, bytesSharedWithPrev int) {
 		curr.compressedDataLen -= (b.bundleCount(b.nKeys) - 1) * curr.blockPrefixLen
 		// The compressedDataLen is the largest offset we'll need to encode in the
 		// offset table.
-		curr.offsetEncoding = DetermineUintEncoding(0, uint64(curr.compressedDataLen))
+		curr.offsetEncoding = DetermineUintEncoding(0, uint64(curr.compressedDataLen), UintEncodingRowThreshold)
 		b.data = append(b.data, key...)
 		b.addOffset(uint32(len(b.data)))
 	}

diff --git a/sstable/colblk/testdata/data_block/rewrite_suffixes b/sstable/colblk/testdata/data_block/rewrite_suffixes
@@ -13,7 +13,7 @@ write
 poi@12#0,SET:big
 yaya@5#0,SET:mini
 ----
-size=110:
+size=102:
 0: prefixes:       prefixbytes(16): 2 keys
 1: suffixes:       bytes: 2 rows set; 5 bytes in data
 2: trailers:       uint: 2 rows
@@ -38,13 +38,13 @@ data block header
  │    ├── 021-022: b 00000010 # col 2: uint
  │    ├── 022-026: x 44000000 # col 2: page start 68
  │    ├── 026-027: b 00000001 # col 3: bool
- │    ├── 027-031: x 4d000000 # col 3: page start 77
+ │    ├── 027-031: x 47000000 # col 3: page start 71
  │    ├── 031-032: b 00000011 # col 4: bytes
- │    ├── 032-036: x 60000000 # col 4: page start 96
+ │    ├── 032-036: x 58000000 # col 4: page start 88
  │    ├── 036-037: b 00000001 # col 5: bool
- │    ├── 037-041: x 6b000000 # col 5: page start 107
+ │    ├── 037-041: x 63000000 # col 5: page start 99
  │    ├── 041-042: b 00000001 # col 6: bool
- │    └── 042-046: x 6c000000 # col 6: page start 108
+ │    └── 042-046: x 64000000 # col 6: page start 100
  ├── data for column 0 (prefixbytes)
  │    ├── 046-047: x 04 # bundle size: 16
  │    ├── offsets table
@@ -68,27 +68,27 @@ data block header
  │         ├── 063-066: x 403132 # data[0]: @12
  │         └── 066-068: x 4035   # data[1]: @5
  ├── data for column 2 (uint)
- │    ├── 068-069: x 80               # encoding: const
- │    └── 069-077: x 0100000000000000 # 64-bit constant: 1
+ │    ├── 068-069: x 01 # encoding: 1b
+ │    ├── 069-070: x 01 # data[0] = 1
+ │    └── 070-071: x 01 # data[1] = 1
  ├── data for column 3 (bool)
- │    ├── 077-078: x 00                                                               # default bitmap encoding
- │    ├── 078-080: x 0000                                                             # padding to align to 64-bit boundary
- │    ├── 080-088: b 0000001100000000000000000000000000000000000000000000000000000000 # bitmap word 0
- │    └── 088-096: b 0000000100000000000000000000000000000000000000000000000000000000 # bitmap summary word 0-63
+ │    ├── 071-072: x 00                                                               # default bitmap encoding
+ │    ├── 072-080: b 0000001100000000000000000000000000000000000000000000000000000000 # bitmap word 0
+ │    └── 080-088: b 0000000100000000000000000000000000000000000000000000000000000000 # bitmap summary word 0-63
  ├── data for column 4 (bytes)
  │    ├── offsets table
- │    │    ├── 096-097: x 01 # encoding: 1b
- │    │    ├── 097-098: x 00 # data[0] = 0 [100 overall]
- │    │    ├── 098-099: x 03 # data[1] = 3 [103 overall]
- │    │    └── 099-100: x 07 # data[2] = 7 [107 overall]
+ │    │    ├── 088-089: x 01 # encoding: 1b
+ │    │    ├── 089-090: x 00 # data[0] = 0 [92 overall]
+ │    │    ├── 090-091: x 03 # data[1] = 3 [95 overall]
+ │    │    └── 091-092: x 07 # data[2] = 7 [99 overall]
  │    └── data
- │         ├── 100-103: x 626967   # data[0]: big
- │         └── 103-107: x 6d696e69 # data[1]: mini
+ │         ├── 092-095: x 626967   # data[0]: big
+ │         └── 095-099: x 6d696e69 # data[1]: mini
  ├── data for column 5 (bool)
- │    └── 107-108: x 01 # zero bitmap encoding
+ │    └── 099-100: x 01 # zero bitmap encoding
  ├── data for column 6 (bool)
- │    └── 108-109: x 01 # zero bitmap encoding
- └── 109-110: x 00 # block padding byte
+ │    └── 100-101: x 01 # zero bitmap encoding
+ └── 101-102: x 00 # block padding byte
 
 rewrite from=@12 to=@22
 ----
@@ -135,7 +135,7 @@ data block header
  │    ├── 021-022: b 00000010 # col 2: uint
  │    ├── 022-026: x 4d000000 # col 2: page start 77
  │    ├── 026-027: b 00000001 # col 3: bool
- │    ├── 027-031: x 56000000 # col 3: page start 86
+ │    ├── 027-031: x 51000000 # col 3: page start 81
  │    ├── 031-032: b 00000011 # col 4: bytes
  │    ├── 032-036: x 68000000 # col 4: page start 104
  │    ├── 036-037: b 00000001 # col 5: bool
@@ -169,11 +169,13 @@ data block header
  │         ├── 073-075: x 4036 # data[1]: @6
  │         └── 075-077: x 4036 # data[2]: @6
  ├── data for column 2 (uint)
- │    ├── 077-078: x 80               # encoding: const
- │    └── 078-086: x 0100000000000000 # 64-bit constant: 1
+ │    ├── 077-078: x 01 # encoding: 1b
+ │    ├── 078-079: x 01 # data[0] = 1
+ │    ├── 079-080: x 01 # data[1] = 1
+ │    └── 080-081: x 01 # data[2] = 1
  ├── data for column 3 (bool)
- │    ├── 086-087: x 00                                                               # default bitmap encoding
- │    ├── 087-088: x 00                                                               # padding to align to 64-bit boundary
+ │    ├── 081-082: x 00                                                               # default bitmap encoding
+ │    ├── 082-088: x 000000000000                                                     # padding to align to 64-bit boundary
  │    ├── 088-096: b 0000011100000000000000000000000000000000000000000000000000000000 # bitmap word 0
  │    └── 096-104: b 0000000100000000000000000000000000000000000000000000000000000000 # bitmap summary word 0-63
  ├── data for column 4 (bytes)
@@ -210,13 +212,13 @@ data block header
  │    ├── 021-022: b 00000010 # col 2: uint
  │    ├── 022-026: x 50000000 # col 2: page start 80
  │    ├── 026-027: b 00000001 # col 3: bool
- │    ├── 027-031: x 59000000 # col 3: page start 89
+ │    ├── 027-031: x 54000000 # col 3: page start 84
  │    ├── 031-032: b 00000011 # col 4: bytes
- │    ├── 032-036: x 70000000 # col 4: page start 112
+ │    ├── 032-036: x 68000000 # col 4: page start 104
  │    ├── 036-037: b 00000001 # col 5: bool
- │    ├── 037-041: x 7e000000 # col 5: page start 126
+ │    ├── 037-041: x 76000000 # col 5: page start 118
  │    ├── 041-042: b 00000001 # col 6: bool
- │    └── 042-046: x 7f000000 # col 6: page start 127
+ │    └── 042-046: x 77000000 # col 6: page start 119
  ├── data for column 0 (prefixbytes)
  │    ├── 046-047: x 04 # bundle size: 16
  │    ├── offsets table
@@ -244,26 +246,28 @@ data block header
  │         ├── 074-077: x 403534 # data[1]: @54
  │         └── 077-080: x 403534 # data[2]: @54
  ├── data for column 2 (uint)
- │    ├── 080-081: x 80               # encoding: const
- │    └── 081-089: x 0100000000000000 # 64-bit constant: 1
+ │    ├── 080-081: x 01 # encoding: 1b
+ │    ├── 081-082: x 01 # data[0] = 1
+ │    ├── 082-083: x 01 # data[1] = 1
+ │    └── 083-084: x 01 # data[2] = 1
  ├── data for column 3 (bool)
- │    ├── 089-090: x 00                                                               # default bitmap encoding
- │    ├── 090-096: x 000000000000                                                     # padding to align to 64-bit boundary
- │    ├── 096-104: b 0000011100000000000000000000000000000000000000000000000000000000 # bitmap word 0
- │    └── 104-112: b 0000000100000000000000000000000000000000000000000000000000000000 # bitmap summary word 0-63
+ │    ├── 084-085: x 00                                                               # default bitmap encoding
+ │    ├── 085-088: x 000000                                                           # padding to align to 64-bit boundary
+ │    ├── 088-096: b 0000011100000000000000000000000000000000000000000000000000000000 # bitmap word 0
+ │    └── 096-104: b 0000000100000000000000000000000000000000000000000000000000000000 # bitmap summary word 0-63
  ├── data for column 4 (bytes)
  │    ├── offsets table
- │    │    ├── 112-113: x 01 # encoding: 1b
- │    │    ├── 113-114: x 00 # data[0] = 0 [117 overall]
- │    │    ├── 114-115: x 03 # data[1] = 3 [120 overall]
- │    │    ├── 115-116: x 06 # data[2] = 6 [123 overall]
- │    │    └── 116-117: x 09 # data[3] = 9 [126 overall]
+ │    │    ├── 104-105: x 01 # encoding: 1b
+ │    │    ├── 105-106: x 00 # data[0] = 0 [109 overall]
+ │    │    ├── 106-107: x 03 # data[1] = 3 [112 overall]
+ │    │    ├── 107-108: x 06 # data[2] = 6 [115 overall]
+ │    │    └── 108-109: x 09 # data[3] = 9 [118 overall]
  │    └── data
- │         ├── 117-120: x 666f6f # data[0]: foo
- │         ├── 120-123: x 626172 # data[1]: bar
- │         └── 123-126: x 626178 # data[2]: bax
+ │         ├── 109-112: x 666f6f # data[0]: foo
+ │         ├── 112-115: x 626172 # data[1]: bar
+ │         └── 115-118: x 626178 # data[2]: bax
  ├── data for column 5 (bool)
- │    └── 126-127: x 01 # zero bitmap encoding
+ │    └── 118-119: x 01 # zero bitmap encoding
  ├── data for column 6 (bool)
- │    └── 127-128: x 01 # zero bitmap encoding
- └── 128-129: x 00 # block padding byte
+ │    └── 119-120: x 01 # zero bitmap encoding
+ └── 120-121: x 00 # block padding byte
diff --git a/sstable/colblk/testdata/keyspan_block b/sstable/colblk/testdata/keyspan_block
@@ -10,7 +10,7 @@ size=37:
 add
 a-b:{(#0,RANGEDEL)}
 ----
-size=57:
+size=50:
 0: user keys:      bytes: 2 rows set; 2 bytes in data
 1: start indices:  uint: 2 rows
 2: trailers:       uint: 1 rows
@@ -232,7 +232,7 @@ size=37:
 add
 b-d:{(#4,RANGEKEYSET,@3,coconut)}
 ----
-size=70:
+size=64:
 0: user keys:      bytes: 2 rows set; 2 bytes in data
 1: start indices:  uint: 2 rows
 2: trailers:       uint: 1 rows
@@ -256,9 +256,9 @@ keyspan-decoder
       │    ├── 21-22: b 00000010 # col 2: uint
       │    ├── 22-26: x 2d000000 # col 2: page start 45
       │    ├── 26-27: b 00000011 # col 3: bytes
-      │    ├── 27-31: x 36000000 # col 3: page start 54
+      │    ├── 27-31: x 30000000 # col 3: page start 48
       │    ├── 31-32: b 00000011 # col 4: bytes
-      │    └── 32-36: x 3b000000 # col 4: page start 59
+      │    └── 32-36: x 35000000 # col 4: page start 53
       ├── data for column 0 (bytes)
       │    ├── offsets table
       │    │    ├── 36-37: x 01 # encoding: 1b
@@ -273,23 +273,23 @@ keyspan-decoder
       │    ├── 43-44: x 00 # data[0] = 0
       │    └── 44-45: x 01 # data[1] = 1
       ├── data for column 2 (uint)
-      │    ├── 45-46: x 80               # encoding: const
-      │    └── 46-54: x 1504000000000000 # 64-bit constant: 1045
+      │    ├── 45-46: x 02   # encoding: 2b
+      │    └── 46-48: x 1504 # data[0] = 1045
       ├── data for column 3 (bytes)
       │    ├── offsets table
-      │    │    ├── 54-55: x 01 # encoding: 1b
-      │    │    ├── 55-56: x 00 # data[0] = 0 [57 overall]
-      │    │    └── 56-57: x 02 # data[1] = 2 [59 overall]
+      │    │    ├── 48-49: x 01 # encoding: 1b
+      │    │    ├── 49-50: x 00 # data[0] = 0 [51 overall]
+      │    │    └── 50-51: x 02 # data[1] = 2 [53 overall]
       │    └── data
-      │         └── 57-59: x 4033 # data[0]: @3
+      │         └── 51-53: x 4033 # data[0]: @3
       ├── data for column 4 (bytes)
       │    ├── offsets table
-      │    │    ├── 59-60: x 01 # encoding: 1b
-      │    │    ├── 60-61: x 00 # data[0] = 0 [62 overall]
-      │    │    └── 61-62: x 07 # data[1] = 7 [69 overall]
+      │    │    ├── 53-54: x 01 # encoding: 1b
+      │    │    ├── 54-55: x 00 # data[0] = 0 [56 overall]
+      │    │    └── 55-56: x 07 # data[1] = 7 [63 overall]
       │    └── data
-      │         └── 62-69: x 636f636f6e7574 # data[0]: coconut
-      └── 69-70: x 00 # block padding byte
+      │         └── 56-63: x 636f636f6e7574 # data[0]: coconut
+      └── 63-64: x 00 # block padding byte
 
 iter
 seek-ge a

diff --git a/sstable/colblk/testdata/uints b/sstable/colblk/testdata/uints
@@ -495,13 +495,18 @@ write
 
 size rows=(6)
 ----
-Size(6, 0) = 9
+Size(6, 0) = 7
 
 finish rows=6
 ----
 uints
- ├── 0-1: x 80               # encoding: const
- └── 1-9: x 0100000000000000 # 64-bit constant: 1
+ ├── 0-1: x 01 # encoding: 1b
+ ├── 1-2: x 01 # data[0] = 1
+ ├── 2-3: x 01 # data[1] = 1
+ ├── 3-4: x 01 # data[2] = 1
+ ├── 4-5: x 01 # data[3] = 1
+ ├── 5-6: x 01 # data[4] = 1
+ └── 6-7: x 01 # data[5] = 1
 
 # Test 32-bit delta encoding.