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Add a bitmap data type stored as a Roaring bitmap - #5344
This PR adds compressed bitmaps to Valkey as a new data type, bitmap, stored
as a Roaring bitmap with the CRoaring library. It follows the
discussion in #1480, and adds the design document requested there: design-docs/roaring-bitmaps.md.
A Valkey bitmap is a string: one byte per eight bits, up to the highest bit set.
A single user id near 2^31 takes 256 MB. Sparse, clustered or skewed bitmaps (user
ids, hashed ids, time series) are common, and Roaring bitmaps store them in a
fraction of the space while making BITCOUNT and BITOP much faster (see the
benchmarks below). Roaring bitmaps are used by Lucene, Spark, Druid, ClickHouse
and many other systems, and Redis 8.12 adopted CRoaring for the same purpose
(redis/redis#15331).
What changes for users
Nothing, unless they create a bitmap:
BITCONVERT key BITMAP converts a string to a bitmap in place (keeping its
bits, its length and its TTL), or creates an empty bitmap for a missing key. BITCONVERT key STRING converts back.
R.IMPORT key payload stores a bitmap from the portable Roaring format,
and R.EXPORT key returns a bitmap or a string in that format, which the
Roaring libraries of C, C++, Java, Go, Rust and Python read and write.
The bit commands (SETBIT, GETBIT, BITCOUNT, BITPOS, BITOP, BITFIELD, BITFIELD_RO) work on strings and on bitmaps, and return the same
results for a bitmap as for the string holding the same bytes. A bit write
keeps the type of its key. BITOP stores a bitmap when a source is a bitmap.
TYPE reports bitmap, OBJECT ENCODING reports roaring. Other string
commands (GET, APPEND, INCR, ...) reply WRONGTYPE for a bitmap.
There is no configuration: the type of every result follows from the command
and its keys, so commands replicate as they are, and no node's settings can
make replicas diverge.
The two questions from the November 9 meeting
A native type or the bitops on strings? Section 7 of the design document
compares the two. An earlier prototype stored Roaring bitmaps as an encoding of
strings (branch).
It is transparent, but every place that reads a string's bytes must handle the
encoding, and a GET on a sparse bitmap silently builds hundreds of megabytes.
This PR makes the bitmap a native type, and keeps as much transparency as
Valkey's conventions allow: the bit commands accept both types, as ZUNIONSTORE
accepts sets, and only BITCONVERT changes a key's type in place.
Inside the core? Roaring modules exist, but a module cannot make the
existing bit commands, TYPE, RDB, replication and slot migration work with a
new representation. The data structure is one vendored library and about 600
lines of glue (src/bitmap_roaring.c).
Overlap with Redis 8.12
Same model: a new type (TYPE bitmap), bit commands on both types, WRONGTYPE
from string commands. Differences (Section 8 of the design document; the Redis
side is taken from the description of redis/redis#15331):
This PR
Redis 8.12
Creating bitmaps
Explicit: BITCONVERT, R.IMPORT, BITOP with a bitmap source
Configuration bitmap-default-roaring (off by default): bit writes create bitmaps and convert strings
Offsets
32-bit (2^32 bits)
64-bit (roaring64)
OBJECT ENCODING
roaring
bitmap-roaring
Getting the bytes
BITCONVERT key STRING
DEBUG BITMAP-RAW
Portable import/export
R.IMPORT, R.EXPORT
none
RDB type
24 (RDB 82)
33 (RDB 16); the formats are already incompatible
Compatibility
RDB: new type RDB_TYPE_BITMAP = 24, RDB version 82. Version 82 is
mapped to 9.3 in RDB_VERSION_MAP as a placeholder, to be set to the release
that ships this. As for path hashes, a bitmap cannot be written for an older
replica: its full sync fails, and newer replicas are not affected (new test in tests/integration/cross-version-replication.tcl).
AOF rewrite and atomic slot migration emit R.IMPORT (plus a SETBIT ... 0
when the length extends past the last set bit).
Modules:VALKEYMODULE_KEYTYPE_BITMAP; ValueLength() returns the length
in bytes.
Existing behavior: one fix, in its own commit. A BITFIELD whose
operations all fail under OVERFLOW FAIL still extends its key, but was not
counted as a write, so the replica kept a shorter value. It now counts as a
write (replicated, AOF, setbit event, WATCH). This also affects strings;
the commit can be sent as a separate PR if preferred.
Dependency
CRoaring (Apache 2.0 or MIT) is vendored unchanged in deps/croaring as its
single-file amalgamation (roaring.c, roaring.h), built from commit b4cc0c48 (5.5.5 plus RoaringBitmap/CRoaring#961). deps/README.md documents
the upgrade steps; REUSE.toml, the Makefiles and CMake are updated. Its
allocations go through zmalloc, and its symbols are hidden from modules.
CRoaring is mature (2016), widely deployed, and its portable format is stable.
Safety
Every payload from outside (R.IMPORT, RESTORE, RDB, full sync) goes through
CRoaring's bounded deserialization and roaring_bitmap_internal_validate(),
always (Section 4.3 of the design document).
Tests
tests/unit/type/bitmap.tcl: the bit commands on a string and on a bitmap
side by side, including a random sequence; BITCONVERT, R.IMPORT, R.EXPORT, invalid payloads, DUMP/RESTORE, DEBUG RELOAD, AOF, replication,
scripts with set_repl, MULTI, keyspace events, size limits.
src/unit/test_bitmap_roaring.cpp: the data structure against a byte array,
and corrupted payloads.
Slot migration (cluster-migrateslots.tcl), cross-version replication, and the
corrupt-dump fuzzer now cover bitmaps.
A differential fuzzer (not part of this PR) ran for 6 hours on the benchmark
machine: 38 workers on release, ASan and UBSan builds, 4.4 million random
steps and 28.7 million commands. Every command runs on a bitmap and on a
string twin, and the replies and the bytes must match. About 8,900
checkpoints compare the replica, the AOF before and after a rewrite, and an
RDB reload, by DEBUG DIGEST. 184,000 corrupted RESTORE and R.IMPORT payloads were sent; the 15,000 that stayed valid were checked for
consistency. No mismatch, sanitizer report or crash. Seven sanitizer workers
stopped early because the harness timed out waiting for DEBUG LOADAOF on
512 MB values.
Benchmarks
Valkey (this branch, strings and bitmaps) against Redis at the merge commit of
its compressed bitmaps (f3b9b68ec, strings and bitmaps), on an Intel Xeon Gold
6548N.
Builds: Valkey uses 32-bit Roaring, with SIMD chosen at runtime. Redis
uses roaring64 (CRoaring 4.7.2), SIMD disabled, as it ships.
Setup: server pinned to one core, client (redis-py) to another, over a Unix
socket.
Timing: server-side (INFO commandstats), commands pipelined, best of 3
interleaved rounds.
Data: each mode loads the same two bitmaps a and b, generated from
the same seed; all modes return the same BITCOUNT for a, b and a AND b. Valkey bitmaps are made with BITCONVERT; Redis bitmaps with a SETBIT under bitmap-default-roaring yes. BITOP writes dst = a op b. GETBIT and SETBIT use random offsets; SETBIT flips a bit and flips it
back.
The charts leave out the 100k random 32-bit ids, whose 512 MB strings would
flatten every other bar; that dataset is in the tables.
Summary:
Memory: Valkey bitmaps are 1.2 to 4.5 times smaller than Redis bitmaps,
except at 50% density, where neither compresses. 100k random 32-bit ids take
746 KB, against 3.1 MB in Redis and 512 MB as a string.
BITCOUNT: about 1.4 µs on the 100M-id bitmaps, against about 24 µs in
Redis and 0.6 to 0.8 ms on strings.
BITOP: about 2 to 10 times faster than Redis bitmaps on random data,
and 4 to 50 times on runs. At 1% density, Redis bitmaps are no faster than
strings, while Valkey bitmaps are about 7 times faster.
Point operations cost a fraction of a microsecond in every mode; bitmaps
are slower than strings (about 0.15 µs against 0.06 µs for GETBIT).
Known slow case:SETBIT that creates or empties a container in a bitmap
with tens of thousands of containers. On the 100k random 32-bit ids (51,000
containers), it takes 1.7 µs against 0.5 µs in Redis: 32-bit Roaring keeps
its containers in a sorted array, which shifts, while roaring64 uses a tree
(design document, Section 2.3). A roaring64 encoding for such bitmaps is a
possible follow-up.
All measurements (µs, except memory)
0.01% random (10k of 100M ids)
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
memory
12.0 MB
36.0 KB
12.0 MB
98.2 KB
GETBIT (µs)
0.06
0.14
0.05
0.14
SETBIT (update) (µs)
0.09
0.21
0.09
0.35
BITCOUNT (µs)
789
1.4
688
24.4
BITPOS 1 (µs)
0.22
0.16
0.22
0.19
BITOP AND (µs)
11,520
235
11,066
453
BITOP OR (µs)
11,696
137
11,058
699
BITOP XOR (µs)
11,560
141
11,421
490
0.1% random (100k of 100M ids)
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
SETBIT (build) (µs)
0.45
0.21
0.40
0.43
memory
14.0 MB
217.4 KB
14.0 MB
336.4 KB
GETBIT (µs)
0.05
0.12
0.06
0.17
SETBIT (update) (µs)
0.09
0.22
0.09
0.40
BITCOUNT (µs)
727
1.4
669
25.1
BITPOS 1 (µs)
0.17
0.17
0.18
0.22
BITOP AND (µs)
7,846
201
11,097
1,632
BITOP OR (µs)
6,535
474
11,466
1,282
BITOP XOR (µs)
6,446
378
11,721
1,302
1% random (1M of 100M ids)
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
memory
12.0 MB
1.9 MB
12.0 MB
2.2 MB
GETBIT (µs)
0.06
0.26
0.06
0.31
SETBIT (update) (µs)
0.10
0.42
0.09
0.64
BITCOUNT (µs)
583
1.4
688
23.7
BITPOS 1 (µs)
0.16
0.23
0.17
0.34
BITOP AND (µs)
7,573
965
10,835
9,949
BITOP OR (µs)
6,059
1,300
10,958
10,956
BITOP XOR (µs)
5,980
1,594
11,720
11,337
50% random (50M of 100M ids)
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
memory
12.0 MB
11.9 MB
12.0 MB
12.0 MB
GETBIT (µs)
0.12
0.17
0.12
0.19
SETBIT (update) (µs)
0.10
0.18
0.09
0.34
BITCOUNT (µs)
796
1.4
705
24.2
BITPOS 1 (µs)
0.13
0.19
0.13
0.15
BITOP AND (µs)
11,304
1,985
10,550
4,597
BITOP OR (µs)
11,948
1,548
10,917
3,192
BITOP XOR (µs)
11,616
1,534
10,939
3,275
10 runs of 1M ids in 100M
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
memory
12.0 MB
2.7 KB
12.0 MB
12.2 KB
GETBIT (µs)
0.07
0.06
0.07
0.09
SETBIT (update) (µs)
0.09
0.16
0.09
0.45
BITCOUNT (µs)
739
0.46
658
2.0
BITPOS 1 (µs)
62.4
0.08
61.3
0.16
BITOP AND (µs)
11,399
1.2
10,899
57.4
BITOP OR (µs)
11,098
15.6
11,027
62.0
BITOP XOR (µs)
11,277
15.9
10,851
57.6
100k random 32-bit ids
Operation
Valkey string
Valkey bitmap
Redis string
Redis bitmap
memory
512.0 MB
746.4 KB
512.0 MB
3.1 MB
GETBIT (µs)
0.07
0.35
0.06
0.28
SETBIT (update) (µs)
0.09
1.7
0.10
0.50
BITCOUNT (µs)
93,242
83.5
53,317
805
BITPOS 1 (µs)
0.86
0.23
0.87
0.27
BITOP AND (µs)
722,635
4,541
685,828
9,517
BITOP OR (µs)
720,510
4,516
696,395
13,011
BITOP XOR (µs)
721,586
4,064
679,401
10,824
Open questions for reviewers
Command names.R.EXPORT/R.IMPORT look like module commands, and R
usually means "right" in Valkey. BITEXPORT/BITIMPORT?
Keyspace events: bit commands keep their events in the string class $;
Redis added a bitmap class.
64-bit offsets (roaring64), possibly as a second encoding for bitmaps
with many containers.
Follow-ups
Documentation in valkey-doc for BITCONVERT, R.EXPORT, R.IMPORT and the bitmap type (needs-doc-pr).
Active defrag and dismissObject() for bitmaps (bitmaps are skipped today).
Reviewing
The five commits are meant to be read in order:
Vendor CRoaring under deps/croaring: the library and its build only.
Replicate a BITFIELD that only extends its key: the fix to existing
behavior described above, independent of the rest.
Add a bitmap data type stored as a Roaring bitmap: the type, its plumbing,
the commands and the tests.
Add a design document for the bitmap data type.
Run the bitmap tests in cluster mode: hash tags and DUMP/RESTORE in
the tests so that they pass against an external cluster.
CRoaring (https://github.com/RoaringBitmap/CRoaring) is the C library
for Roaring bitmaps, a compressed bitmap format. It is dual-licensed
under Apache-2.0 and MIT.
roaring.c and roaring.h are the amalgamation of CRoaring at commit
b4cc0c48cd608addf91cf1595b2f268d9b2d2e66, unchanged: release 5.5.5 plus
RoaringBitmap/CRoaring#961 (faster range cardinality and flip). They
are built with CRoaring's amalgamation.sh in the C locale, which gives
the release files when run at a release tag. ROARING_VERSION still
reads 5.5.5.
The local Makefile and CMakeLists.txt build them as a static library
with symbols hidden from modules; the SIMD code paths (AVX2 and AVX-512
on x64, NEON on ARM) are selected at runtime. deps/README.md describes
how to upgrade.
The library is linked into the server and the unit tests, but nothing
uses it yet.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
A BITFIELD whose write operations all fail under OVERFLOW FAIL still
creates or extends the key to cover the highest offset it writes. It did
not increment server.dirty, so it was neither replicated nor written to
the AOF, and the replica kept a shorter value. Count the creation or
extension as a change.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
Bitmaps are strings: a bitmap costs one byte per eight bits up to its
highest bit, so one bit near 2^31 takes 256 MB (valkey-io#1480). This adds a
bitmap data type stored as a compressed Roaring bitmap
(https://roaringbitmap.org), with CRoaring.
- TYPE reports "bitmap", OBJECT ENCODING "roaring". A bitmap holds up to
2^32 bits. It keeps the length in bytes of the equivalent string, so
the bit commands return the same results for both types.
- SETBIT, GETBIT, BITCOUNT, BITPOS, BITOP, BITFIELD and BITFIELD_RO work
on strings and bitmaps. A bit write keeps the type of its key; BITOP
stores a bitmap when a source is a bitmap and the result fits one.
Other string commands reply WRONGTYPE. A write past bit 2^32 - 1 of a
bitmap is an error.
- BITCONVERT key BITMAP|STRING converts a key between the two types,
keeping its bits, length and TTL, and creates an empty bitmap for a
missing key. It is the only command that changes a key's type in
place.
- R.EXPORT and R.IMPORT exchange bitmaps in the portable Roaring format,
read by the Roaring libraries of most languages.
There is no configuration: the type of every result follows from the
command and its keys, so every command propagates as is.
Persistence and replication:
- A new RDB type, RDB_TYPE_BITMAP (24), in RDB version 82: the length
in bytes, then the portable serialization. As for path hashes, it
cannot be written for older RDB targets.
- AOF rewrite and slot migration emit R.IMPORT, then SETBIT to restore
the length.
- Every payload from outside (R.IMPORT, RESTORE, RDB) is read with
CRoaring's bounded deserialization and checked with
roaring_bitmap_internal_validate().
Also: MEMORY USAGE, lazy free effort, COPY, SCAN TYPE, DEBUG DIGEST
(over the bits of each chunk, so independent of the containers), the
module key type VALKEYMODULE_KEYTYPE_BITMAP and valkey-check-rdb.
Active defrag skips bitmaps for now. Bit commands keep their keyspace
events in the string class.
Tested by tests/unit/type/bitmap.tcl, which compares every bit command
on a string and a bitmap, and covers RDB, DUMP/RESTORE, AOF, replication
and keyspace events; by src/unit/test_bitmap_roaring.cpp, which
compares the data structure with a byte array and feeds it corrupted
payloads; and by slot migration, cross-version replication and
corrupt-dump fuzzer tests.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
It describes the data model, the commands, persistence, replication,
and compares a new type with a string encoding, and with the compressed
bitmaps of Redis 8.12, as asked in valkey-io#1480.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
The external cluster tests failed with CROSSSLOT: some bitmap tests
used several keys in one command. Copy values with DUMP and RESTORE,
delete keys one by one, and give the keys of the multi-key tests (BITOP,
COPY, EVAL) the same hash tag.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
This change adds a CRoaring-backed bitmap object, extends bit commands to support bitmap values, and adds BITCONVERT, R.EXPORT, and R.IMPORT. It adds bitmap serialization to RDB and AOF paths and integrates bitmap values with server object handling, replication, and tests.
Adds the vendored CRoaring source, license, and build rules. Build files link it into the server and unit tests.
Implement bitmap storage and object support src/bitmap_roaring.*, src/server.*, src/object.c, src/db.c, src/debug.c, src/defrag.c, src/lazyfree.c, src/module.c, src/valkeymodule.h, src/valkey-check-rdb.c, design-docs/roaring-bitmaps.md, src/unit/test_bitmap_roaring.cpp
Adds bitmap object operations and server object handling. Integrates bitmap values with module type and length reporting, digest, memory accounting, copying, and diagnostics. The design document describes the representation and integration. Unit tests cover object operations and serialization.
Add bitmap commands and string-compatible bit operations src/bitops.c, src/commands.def, src/commands/{bitconvert.json,r.export.json,r.import.json}, src/server.h, utils/generate-command-code.py, tests/unit/type/bitmap.tcl, tests/unit/bitfield.tcl, tests/support/util.tcl, tests/unit/introspection-2.tcl
Extends bit commands to support bitmap values and adds conversion and portable import/export commands. Tests cover command behavior, type handling, limits, and bitfield extension.
Adds RDB type 24 in RDB version 82 and bitmap serialization to RDB loading, saving, and AOF rewriting. Tests cover persistence, replication, migration, RDB inspection, and corrupt bitmap data.
The title "Add a bitmap data type stored as a Roaring bitmap" names the main change. The changeset adds a native bitmap type backed by CRoaring, with BITCONVERT, R.IMPORT, R.EXPORT, RDB, AOF, replicat…
Description check
The description states that the PR adds a compressed bitmap type stored as a Roaring bitmap using CRoaring. It explains the new commands (BITCONVERT, R.IMPORT, R.EXPORT), compatibility changes (RDB 82…
Linked Issues check
[#1480] requests Roaring bitmap support to reduce memory for sparse user-ID bitmaps with offsets up to 2,147,483,647. Its stated feature is "Support Roaring Bitmaps with new Commands". The PR implemen…
Out of Scope Changes check
The changes map to the [#1480] feature. The CRoaring vendoring, build files, license and README (deps/croaring, deps/Makefile, deps/README.md, REUSE.toml, src/Makefile, src/CMakeLists.txt, src/unit bu…
Full details: Title check
Explanation
The title "Add a bitmap data type stored as a Roaring bitmap" names the main change. The changeset adds a native bitmap type backed by CRoaring, with BITCONVERT, R.IMPORT, R.EXPORT, RDB, AOF, replication, and bit-command support. The title is specific and matches the primary objective in the PR objectives.
Full details: Description check
Explanation
The description states that the PR adds a compressed bitmap type stored as a Roaring bitmap using CRoaring. It explains the new commands (BITCONVERT, R.IMPORT, R.EXPORT), compatibility changes (RDB 82, AOF rewrite, slot migration, modules), the vendored dependency, tests, and benchmarks. It is closely related to the changeset.
Full details: Linked Issues check
Explanation
[#1480] requests Roaring bitmap support to reduce memory for sparse user-ID bitmaps with offsets up to 2,147,483,647. Its stated feature is "Support Roaring Bitmaps with new Commands". The PR implements that feature. It adds a CRoaring-backed bitmap type (src/bitmap_roaring.c, src/bitmap_roaring.h), the BITCONVERT, R.IMPORT and R.EXPORT commands (src/bitops.c, src/commands/*.json), and bit-command support for bitmap values (src/bitops.c). The PR summary and benchmarks report large memory reductions for sparse bitmaps. The summary also reports faster BITCOUNT and BITOP. The issue sets no numeric performance threshold, so the slower bitmap GETBIT and SETBIT do not fail a stated requirement. The tests cover high offsets, string-to-bitmap parity, persistence, replication, migration and invalid payloads (tests/unit/type/bitmap.tcl, src/unit/test_bitmap_roaring.cpp). The PR uses a native type, not the issue's optional bitmap_engine configuration. The issue presents that configuration as an alternative, so this choice does not violate a requirement. Evidence limit: this assessment relies on the whole-PR summary. The incremental changes since the previous reviewed heads were not inspected in detail.
Full details: Out of Scope Changes check
Explanation
The changes map to the [#1480] feature. The CRoaring vendoring, build files, license and README (deps/croaring, deps/Makefile, deps/README.md, REUSE.toml, src/Makefile, src/CMakeLists.txt, src/unit build files) support the new data structure. Object, RDB, AOF, module, debug, defrag, lazyfree and COPY/SCAN plumbing (src/object.c, src/rdb.c, src/aof.c, src/module.c, src/db.c, src/defrag.c, src/lazyfree.c) support the new type. Command metadata and the generator change in utils/generate-command-code.py support the new commands. Tests and the design document support the feature. The BITFIELD write-tracking fix in src/bitops.c, with its replication test in tests/unit/bitfield.tcl, is a change to shared behavior that also affects strings. The bitmap path also uses this code, and the PR description states the fix is separable. It is not shown to be unrelated, so it does not fail the check. Evidence limit: this assessment relies on the whole-PR summary, not a full diff read.
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Files selected for processing: 3
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Ready for human review.
Since the last review the head adds only coverage tests: BITPOS 0 bisection, BITOP OR/XOR over many sources, BITFIELD reads near 2^32, module ValueLength, and check-rdb bitmap stats. Their expected values match the code. The merge from unstable does not touch the PR's own code. No open findings.
Risk: High. Adds a new object type and RDB version 82 that touch persistence, full sync, AOF rewrite and slot migration. A bug here could corrupt or lose bitmap keys on reload or on replicas.
Open findings: none.
Resolved (1)
(minor) tests/unit/type/bitmap.tcl:223 Config and DEBUG toggles (proto-max-bulk-len, notify-keyspace-events, set-skip-checksum-validation) were restored only after the assertions, so one failing test leaked its setting into later cases.
Backport: Needed for 9.2, 9.1, 9.0, 8.1, 8.0, 7.2. Only commit 3b98919 needs a backport. On all six release lines bitfieldGeneric bumps changes only on a successful write, so a BITFIELD that only extends its key under OVERFLOW FAIL is missed by the replica and the AOF. The bitmap type itself is a feature.
Updated for 994c3fe at 2026-11-12 16:42 UTC. The bot rewrites this comment on every review.
Use test_config_set and test_defer so that proto-max-bulk-len,
notify-keyspace-events and the DEBUG checksum toggle are restored
when an assertion fails, instead of leaking into later tests.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
❌ Patch coverage is 98.18653% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.54%. Comparing base (6f6ec61) to head (994c3fe).
Cover the bisection of BITPOS 0 after a long run of ones, the pairing
of an odd number of sparse BITOP OR/XOR sources, BITFIELD reads past
the last bit of a bitmap, the length of a bitmap seen by a module, and
bitmap stats in valkey-check-rdb.
Signed-off-by: Daniel Lemire <daniel@lemire.me>
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tests/unit/moduleapi/hooks.tcl
tests/unit/type/bitmap.tcl
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This PR adds compressed bitmaps to Valkey as a new data type,
bitmap, storedas a Roaring bitmap with the
CRoaring library. It follows the
discussion in #1480, and adds the design document requested there:
design-docs/roaring-bitmaps.md.Fixes #1480
Why
A Valkey bitmap is a string: one byte per eight bits, up to the highest bit set.
A single user id near 2^31 takes 256 MB. Sparse, clustered or skewed bitmaps (user
ids, hashed ids, time series) are common, and Roaring bitmaps store them in a
fraction of the space while making
BITCOUNTandBITOPmuch faster (see thebenchmarks below). Roaring bitmaps are used by Lucene, Spark, Druid, ClickHouse
and many other systems, and Redis 8.12 adopted CRoaring for the same purpose
(redis/redis#15331).
What changes for users
Nothing, unless they create a bitmap:
BITCONVERT key BITMAPconverts a string to a bitmap in place (keeping itsbits, its length and its TTL), or creates an empty bitmap for a missing key.
BITCONVERT key STRINGconverts back.R.IMPORT key payloadstores a bitmap from theportable Roaring format,
and
R.EXPORT keyreturns a bitmap or a string in that format, which theRoaring libraries of C, C++, Java, Go, Rust and Python read and write.
SETBIT,GETBIT,BITCOUNT,BITPOS,BITOP,BITFIELD,BITFIELD_RO) work on strings and on bitmaps, and return the sameresults for a bitmap as for the string holding the same bytes. A bit write
keeps the type of its key.
BITOPstores a bitmap when a source is a bitmap.TYPEreportsbitmap,OBJECT ENCODINGreportsroaring. Other stringcommands (
GET,APPEND,INCR, ...) replyWRONGTYPEfor a bitmap.There is no configuration: the type of every result follows from the command
and its keys, so commands replicate as they are, and no node's settings can
make replicas diverge.
The two questions from the November 9 meeting
A native type or the bitops on strings? Section 7 of the design document
compares the two. An earlier prototype stored Roaring bitmaps as an encoding of
strings (branch).
It is transparent, but every place that reads a string's bytes must handle the
encoding, and a
GETon a sparse bitmap silently builds hundreds of megabytes.This PR makes the bitmap a native type, and keeps as much transparency as
Valkey's conventions allow: the bit commands accept both types, as
ZUNIONSTOREaccepts sets, and only
BITCONVERTchanges a key's type in place.Inside the core? Roaring modules exist, but a module cannot make the
existing bit commands,
TYPE, RDB, replication and slot migration work with anew representation. The data structure is one vendored library and about 600
lines of glue (
src/bitmap_roaring.c).Overlap with Redis 8.12
Same model: a new type (
TYPE bitmap), bit commands on both types,WRONGTYPEfrom string commands. Differences (Section 8 of the design document; the Redis
side is taken from the description of redis/redis#15331):
BITCONVERT,R.IMPORT,BITOPwith a bitmap sourcebitmap-default-roaring(off by default): bit writes create bitmaps and convert stringsroaring64)OBJECT ENCODINGroaringbitmap-roaringBITCONVERT key STRINGDEBUG BITMAP-RAWR.IMPORT,R.EXPORTCompatibility
RDB_TYPE_BITMAP = 24, RDB version 82. Version 82 ismapped to 9.3 in
RDB_VERSION_MAPas a placeholder, to be set to the releasethat ships this. As for path hashes, a bitmap cannot be written for an older
replica: its full sync fails, and newer replicas are not affected (new test in
tests/integration/cross-version-replication.tcl).R.IMPORT(plus aSETBIT ... 0when the length extends past the last set bit).
VALKEYMODULE_KEYTYPE_BITMAP;ValueLength()returns the lengthin bytes.
BITFIELDwhoseoperations all fail under
OVERFLOW FAILstill extends its key, but was notcounted as a write, so the replica kept a shorter value. It now counts as a
write (replicated, AOF,
setbitevent,WATCH). This also affects strings;the commit can be sent as a separate PR if preferred.
Dependency
CRoaring (Apache 2.0 or MIT) is vendored unchanged in
deps/croaringas itssingle-file amalgamation (
roaring.c,roaring.h), built from commitb4cc0c48(5.5.5 plus RoaringBitmap/CRoaring#961).deps/README.mddocumentsthe upgrade steps;
REUSE.toml, the Makefiles and CMake are updated. Itsallocations go through
zmalloc, and its symbols are hidden from modules.CRoaring is mature (2016), widely deployed, and its portable format is stable.
Safety
Every payload from outside (
R.IMPORT,RESTORE, RDB, full sync) goes throughCRoaring's bounded deserialization and
roaring_bitmap_internal_validate(),always (Section 4.3 of the design document).
Tests
tests/unit/type/bitmap.tcl: the bit commands on a string and on a bitmapside by side, including a random sequence;
BITCONVERT,R.IMPORT,R.EXPORT, invalid payloads,DUMP/RESTORE,DEBUG RELOAD, AOF, replication,scripts with
set_repl,MULTI, keyspace events, size limits.src/unit/test_bitmap_roaring.cpp: the data structure against a byte array,and corrupted payloads.
cluster-migrateslots.tcl), cross-version replication, and thecorrupt-dump fuzzer now cover bitmaps.
machine: 38 workers on release, ASan and UBSan builds, 4.4 million random
steps and 28.7 million commands. Every command runs on a bitmap and on a
string twin, and the replies and the bytes must match. About 8,900
checkpoints compare the replica, the AOF before and after a rewrite, and an
RDB reload, by
DEBUG DIGEST. 184,000 corruptedRESTOREandR.IMPORTpayloads were sent; the 15,000 that stayed valid were checked forconsistency. No mismatch, sanitizer report or crash. Seven sanitizer workers
stopped early because the harness timed out waiting for
DEBUG LOADAOFon512 MB values.
Benchmarks
Valkey (this branch, strings and bitmaps) against Redis at the merge commit of
its compressed bitmaps (
f3b9b68ec, strings and bitmaps), on an Intel Xeon Gold6548N.
uses
roaring64(CRoaring 4.7.2), SIMD disabled, as it ships.socket.
INFO commandstats), commands pipelined, best of 3interleaved rounds.
aandb, generated fromthe same seed; all modes return the same
BITCOUNTfora,banda AND b. Valkey bitmaps are made withBITCONVERT; Redis bitmaps with aSETBITunderbitmap-default-roaring yes.BITOPwritesdst = a op b.GETBITandSETBITuse random offsets;SETBITflips a bit and flips itback.
The charts leave out the 100k random 32-bit ids, whose 512 MB strings would
flatten every other bar; that dataset is in the tables.
Summary:
except at 50% density, where neither compresses. 100k random 32-bit ids take
746 KB, against 3.1 MB in Redis and 512 MB as a string.
BITCOUNT: about 1.4 µs on the 100M-id bitmaps, against about 24 µs inRedis and 0.6 to 0.8 ms on strings.
BITOP: about 2 to 10 times faster than Redis bitmaps on random data,and 4 to 50 times on runs. At 1% density, Redis bitmaps are no faster than
strings, while Valkey bitmaps are about 7 times faster.
are slower than strings (about 0.15 µs against 0.06 µs for
GETBIT).SETBITthat creates or empties a container in a bitmapwith tens of thousands of containers. On the 100k random 32-bit ids (51,000
containers), it takes 1.7 µs against 0.5 µs in Redis: 32-bit Roaring keeps
its containers in a sorted array, which shifts, while
roaring64uses a tree(design document, Section 2.3). A
roaring64encoding for such bitmaps is apossible follow-up.
All measurements (µs, except memory)
0.01% random (10k of 100M ids)
0.1% random (100k of 100M ids)
1% random (1M of 100M ids)
50% random (50M of 100M ids)
10 runs of 1M ids in 100M
100k random 32-bit ids
Open questions for reviewers
R.EXPORT/R.IMPORTlook like module commands, andRusually means "right" in Valkey.
BITEXPORT/BITIMPORT?$;Redis added a bitmap class.
roaring64), possibly as a second encoding for bitmapswith many containers.
Follow-ups
BITCONVERT,R.EXPORT,R.IMPORTand thebitmaptype (needs-doc-pr).dismissObject()for bitmaps (bitmaps are skipped today).Reviewing
The five commits are meant to be read in order:
Vendor CRoaring under deps/croaring: the library and its build only.Replicate a BITFIELD that only extends its key: the fix to existingbehavior described above, independent of the rest.
Add a bitmap data type stored as a Roaring bitmap: the type, its plumbing,the commands and the tests.
Add a design document for the bitmap data type.Run the bitmap tests in cluster mode: hash tags andDUMP/RESTOREinthe tests so that they pass against an external cluster.