[v4,09/15] commit-graph: write Bloom filters to commit graph file
diff mbox series

Message ID ff6b96aad1e2317d3ed36c2c8b419905dea84a83.1586192395.git.gitgitgadget@gmail.com
State New
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Series
  • Changed Paths Bloom Filters
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Commit Message

Johannes Schindelin via GitGitGadget April 6, 2020, 4:59 p.m. UTC
From: Garima Singh <garima.singh@microsoft.com>

Update the technical documentation for commit-graph-format with
the formats for the Bloom filter index (BIDX) and Bloom filter
data (BDAT) chunks. Write the computed Bloom filters information
to the commit graph file using this format.

Helped-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Garima Singh <garima.singh@microsoft.com>
---
 .../technical/commit-graph-format.txt         |  30 +++++
 commit-graph.c                                | 113 +++++++++++++++++-
 commit-graph.h                                |   5 +
 3 files changed, 147 insertions(+), 1 deletion(-)

Comments

SZEDER Gábor May 29, 2020, 8:57 a.m. UTC | #1
On Mon, Apr 06, 2020 at 04:59:49PM +0000, Garima Singh via GitGitGadget wrote:
> From: Garima Singh <garima.singh@microsoft.com>
> 
> Update the technical documentation for commit-graph-format with
> the formats for the Bloom filter index (BIDX) and Bloom filter
> data (BDAT) chunks. Write the computed Bloom filters information
> to the commit graph file using this format.
> 
> Helped-by: Derrick Stolee <dstolee@microsoft.com>
> Signed-off-by: Garima Singh <garima.singh@microsoft.com>
> ---
>  .../technical/commit-graph-format.txt         |  30 +++++
>  commit-graph.c                                | 113 +++++++++++++++++-
>  commit-graph.h                                |   5 +
>  3 files changed, 147 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
> index a4f17441aed..de56f9f1efd 100644
> --- a/Documentation/technical/commit-graph-format.txt
> +++ b/Documentation/technical/commit-graph-format.txt
> @@ -17,6 +17,9 @@ metadata, including:
>  - The parents of the commit, stored using positional references within
>    the graph file.
>  
> +- The Bloom filter of the commit carrying the paths that were changed between
> +  the commit and its first parent, if requested.
> +
>  These positional references are stored as unsigned 32-bit integers
>  corresponding to the array position within the list of commit OIDs. Due
>  to some special constants we use to track parents, we can store at most
> @@ -93,6 +96,33 @@ CHUNK DATA:
>        positions for the parents until reaching a value with the most-significant
>        bit on. The other bits correspond to the position of the last parent.
>  
> +  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
> +    * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all

This is inconsistent with the implementation: according to the code in
one of the previous patches these entries are simple byte offsets, not
8-byte word offsets, i.e. the combined size of all modified path
Bloom filters can be at most 2^32 bytes.

The commit-graph file can contain information about at most 2^31-1
commits.  This means that with that many commits each commit can have
a merely 2 byte Bloom filter on average.  When using 7 hashes we'd
need 10 bits per path, so in two bytes we could store only a single
path.

Clearly, using 4 byte index entries significantly lowers the max
number of commits that can be stored with modified path Bloom filters.
IMO every new chunk must support at least 2^31-1 commits.

> +      Bloom filters from commit 0 to commit i (inclusive) in lexicographic
> +      order. The Bloom filter for the i-th commit spans from BIDX[i-1] to
> +      BIDX[i] (plus header length), where BIDX[-1] is 0.
> +    * The BIDX chunk is ignored if the BDAT chunk is not present.
> +
> +  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
> +    * It starts with header consisting of three unsigned 32-bit integers:
> +      - Version of the hash algorithm being used. We currently only support
> +	value 1 which corresponds to the 32-bit version of the murmur3 hash
> +	implemented exactly as described in
> +	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
> +	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
> +	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
> +	in Probabilistic Verification"

How should double hashing compute the k hashes, i.e. using 64 bit or
32 bit unsigned integer arithmetic?

I'm puzzled that you link to this paper and still use double hashing.

Two of the contributions of that paper are that it points out some
shortcomings of the double hashing scheme and provides a better
alternative in the form of enhanced double hashing, which can cut the
false positive rate in half.

However, that paper considers the hashing scheme only in the context
of one big Bloom filter.  I've found that when it comes to many small
Bloom filters then the k hashes produced by any double hashing variant
are not independent enough, and "standard" double hashing fares the
worst among them.  There are real repositories out there where double
hashing has over an order of magnitude higher average false positive
rate than enhanced double hashing.  Though that's not to say that
enhanced double hashing is good...

For details on these issues see

  https://public-inbox.org/git/20200529085038.26008-16-szeder.dev@gmail.com

> +      - The number of times a path is hashed and hence the number of bit positions
> +	      that cumulatively determine whether a file is present in the commit.
> +      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
> +	      contains 'n' entries, then the filter size is the minimum number of 64-bit
> +	      words that contain n*b bits.

Since the ideal number of bits per element depends only on the number
of hashes per path (k / ln(2) ≈ k * 10 / 7), why is this value stored
in the commit-graph?

> +    * The rest of the chunk is the concatenation of all the computed Bloom
> +      filters for the commits in lexicographic order.
> +    * Note: Commits with no changes or more than 512 changes have Bloom filters
> +      of length zero.

What does this "Note:" prefix mean in the file format specification?

Can an implementation use a one byte Bloom filter with no bits set for
a commit with no changes?  Can an implementation still store a Bloom
filter for commits that modify more than 512 paths?

> +    * The BDAT chunk is present if and only if BIDX is present.
> +
>    Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
>        This list of H-byte hashes describe a set of B commit-graph files that
>        form a commit-graph chain. The graph position for the ith commit in this
> diff --git a/commit-graph.c b/commit-graph.c
> index 732c81fa1b2..a8b6b5cca5d 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c

> @@ -1034,6 +1071,59 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
>  	}
>  }
>  
> +static void write_graph_chunk_bloom_indexes(struct hashfile *f,
> +					    struct write_commit_graph_context *ctx)
> +{
> +	struct commit **list = ctx->commits.list;
> +	struct commit **last = ctx->commits.list + ctx->commits.nr;
> +	uint32_t cur_pos = 0;
> +	struct progress *progress = NULL;
> +	int i = 0;
> +
> +	if (ctx->report_progress)
> +		progress = start_delayed_progress(
> +			_("Writing changed paths Bloom filters index"),
> +			ctx->commits.nr);
> +
> +	while (list < last) {
> +		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
> +		cur_pos += filter->len;

Given a sufficiently large number of commits with large enough Bloom
filters this will silently overflow.

> +		display_progress(progress, ++i);
> +		hashwrite_be32(f, cur_pos);
> +		list++;
> +	}
> +
> +	stop_progress(&progress);
> +}
Derrick Stolee May 29, 2020, 1:35 p.m. UTC | #2
On 5/29/2020 4:57 AM, SZEDER Gábor wrote:
> On Mon, Apr 06, 2020 at 04:59:49PM +0000, Garima Singh via GitGitGadget wrote:
>> From: Garima Singh <garima.singh@microsoft.com>
>>
>> Update the technical documentation for commit-graph-format with
>> the formats for the Bloom filter index (BIDX) and Bloom filter
>> data (BDAT) chunks. Write the computed Bloom filters information
>> to the commit graph file using this format.
>>
>> Helped-by: Derrick Stolee <dstolee@microsoft.com>
>> Signed-off-by: Garima Singh <garima.singh@microsoft.com>
>> ---
>>  .../technical/commit-graph-format.txt         |  30 +++++
>>  commit-graph.c                                | 113 +++++++++++++++++-
>>  commit-graph.h                                |   5 +
>>  3 files changed, 147 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
>> index a4f17441aed..de56f9f1efd 100644
>> --- a/Documentation/technical/commit-graph-format.txt
>> +++ b/Documentation/technical/commit-graph-format.txt
>> @@ -17,6 +17,9 @@ metadata, including:
>>  - The parents of the commit, stored using positional references within
>>    the graph file.
>>  
>> +- The Bloom filter of the commit carrying the paths that were changed between
>> +  the commit and its first parent, if requested.
>> +
>>  These positional references are stored as unsigned 32-bit integers
>>  corresponding to the array position within the list of commit OIDs. Due
>>  to some special constants we use to track parents, we can store at most
>> @@ -93,6 +96,33 @@ CHUNK DATA:
>>        positions for the parents until reaching a value with the most-significant
>>        bit on. The other bits correspond to the position of the last parent.
>>  
>> +  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
>> +    * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all
> 
> This is inconsistent with the implementation: according to the code in
> one of the previous patches these entries are simple byte offsets, not
> 8-byte word offsets, i.e. the combined size of all modified path
> Bloom filters can be at most 2^32 bytes.

The documentation was fixed in 88093289cdc (Documentation: changed-path Bloom
filters use byte words, 2020-05-11).

> The commit-graph file can contain information about at most 2^31-1
> commits.  This means that with that many commits each commit can have
> a merely 2 byte Bloom filter on average.  When using 7 hashes we'd
> need 10 bits per path, so in two bytes we could store only a single
> path.
> 
> Clearly, using 4 byte index entries significantly lowers the max
> number of commits that can be stored with modified path Bloom filters.

This is a good point, and certainly the reason for 8-byte multiples.

> IMO every new chunk must support at least 2^31-1 commits.

I'm not sure this is a valid requirement. Even extremely large repositories
(that are created by actual use, not synthetic) are on the scale of 2^24
commits.

You are right that we should make the commit-graph write process more robust
to reaching these limits. You point out that we have a new limit when these
filters are enabled.

For reference, the Windows OS repo has ~4.25 million commits and the
commit-graph file with changed-path Bloom filters is around 520mb. That's
the whole file size, and without the filters it's around 240mb, so the
filters are taking <300mb ~ 2^29 and we would need to grow the repo by 8x
to hit this limit. That's not an unreasonable amount of growth, but is
also far enough away that we can handle it in time.

The incremental commit-graph can actually save us here (and is similar to
how we solved a scale issue in Azure Repos around the multi-pack-index):
we can refuse to merge layers of an incremental commit-graph if the
changed-path filters would exceed the size limit. Of course, the _first_
write of such a commit-graph would need to be aware of this limit and
plan for it in advance, but that's also a theoretical issue.

I'm tracking some follow-up work [1] for the changed-path filters,
including a way to limit the number of filters computed in one
"git commit-graph write" process. I'll make note of your concerns here,
too.

[1] https://github.com/microsoft/git/issues/272

>> +      Bloom filters from commit 0 to commit i (inclusive) in lexicographic
>> +      order. The Bloom filter for the i-th commit spans from BIDX[i-1] to
>> +      BIDX[i] (plus header length), where BIDX[-1] is 0.
>> +    * The BIDX chunk is ignored if the BDAT chunk is not present.
>> +
>> +  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
>> +    * It starts with header consisting of three unsigned 32-bit integers:
>> +      - Version of the hash algorithm being used. We currently only support
>> +	value 1 which corresponds to the 32-bit version of the murmur3 hash
>> +	implemented exactly as described in
>> +	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
>> +	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
>> +	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
>> +	in Probabilistic Verification"
> 
> How should double hashing compute the k hashes, i.e. using 64 bit or
> 32 bit unsigned integer arithmetic?
> 
> I'm puzzled that you link to this paper and still use double hashing.
> 
> Two of the contributions of that paper are that it points out some
> shortcomings of the double hashing scheme and provides a better
> alternative in the form of enhanced double hashing, which can cut the
> false positive rate in half.
> 
> However, that paper considers the hashing scheme only in the context
> of one big Bloom filter.  I've found that when it comes to many small
> Bloom filters then the k hashes produced by any double hashing variant
> are not independent enough, and "standard" double hashing fares the
> worst among them.  There are real repositories out there where double
> hashing has over an order of magnitude higher average false positive
> rate than enhanced double hashing.  Though that's not to say that
> enhanced double hashing is good...
> 
> For details on these issues see
> 
>   https://public-inbox.org/git/20200529085038.26008-16-szeder.dev@gmail.com

That message includes very detailed experimental analysis, which is nice.
We will need to do some concrete side-by-side comparisons to see if there
actually is a meaningful difference. (You may have already done this.)

>> +      - The number of times a path is hashed and hence the number of bit positions
>> +	      that cumulatively determine whether a file is present in the commit.
>> +      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
>> +	      contains 'n' entries, then the filter size is the minimum number of 64-bit
>> +	      words that contain n*b bits.
> 
> Since the ideal number of bits per element depends only on the number
> of hashes per path (k / ln(2) ≈ k * 10 / 7), why is this value stored
> in the commit-graph?

The ideal number depends also on what false-positive rate you want. In a
hypothetical future where we want to allow customization here, we want
the filters to be consistently sized across all filters.

>> +    * The rest of the chunk is the concatenation of all the computed Bloom
>> +      filters for the commits in lexicographic order.
>> +    * Note: Commits with no changes or more than 512 changes have Bloom filters
>> +      of length zero.
> 
> What does this "Note:" prefix mean in the file format specification?
> 
> Can an implementation use a one byte Bloom filter with no bits set for
> a commit with no changes?  Can an implementation still store a Bloom
> filter for commits that modify more than 512 paths?

This is currently due to a hard-coded value in the implementation. It's not a
requirement of the file format.

>> +    * The BDAT chunk is present if and only if BIDX is present.
>> +
>>    Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
>>        This list of H-byte hashes describe a set of B commit-graph files that
>>        form a commit-graph chain. The graph position for the ith commit in this
>> diff --git a/commit-graph.c b/commit-graph.c
>> index 732c81fa1b2..a8b6b5cca5d 100644
>> --- a/commit-graph.c
>> +++ b/commit-graph.c
> 
>> @@ -1034,6 +1071,59 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
>>  	}
>>  }
>>  
>> +static void write_graph_chunk_bloom_indexes(struct hashfile *f,
>> +					    struct write_commit_graph_context *ctx)
>> +{
>> +	struct commit **list = ctx->commits.list;
>> +	struct commit **last = ctx->commits.list + ctx->commits.nr;
>> +	uint32_t cur_pos = 0;
>> +	struct progress *progress = NULL;
>> +	int i = 0;
>> +
>> +	if (ctx->report_progress)
>> +		progress = start_delayed_progress(
>> +			_("Writing changed paths Bloom filters index"),
>> +			ctx->commits.nr);
>> +
>> +	while (list < last) {
>> +		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
>> +		cur_pos += filter->len;
> 
> Given a sufficiently large number of commits with large enough Bloom
> filters this will silently overflow.

Worth fixing, but we are not in a rush. I noted it in my GitHub issue.

Thanks,
-Stolee
SZEDER Gábor May 31, 2020, 5:23 p.m. UTC | #3
On Fri, May 29, 2020 at 09:35:17AM -0400, Derrick Stolee wrote:
> >> +  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
> >> +    * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all
> > 
> > This is inconsistent with the implementation: according to the code in
> > one of the previous patches these entries are simple byte offsets, not
> > 8-byte word offsets, i.e. the combined size of all modified path
> > Bloom filters can be at most 2^32 bytes.
> 
> The documentation was fixed in 88093289cdc (Documentation: changed-path Bloom
> filters use byte words, 2020-05-11).

Oh, good.  I'm waaay behind the curve and haven't seen this fix.  Even
better, now I also noticed that two bugs I was about to report have
been fixed already (though both fixes have minor flaws).

Ok, so at least the specs are consistent with the implementation.  I'm
not sure this was done in the right direction, though, because too
small Bloom filters do hurt performance.

> > Clearly, using 4 byte index entries significantly lowers the max
> > number of commits that can be stored with modified path Bloom filters.
> 
> This is a good point, and certainly the reason for 8-byte multiples.

Note that Bloom filters with power-of-two number of bits have higher
false positive probabilities when using some form of double hashing.
When going for 8 byte blocks all commits modifying <= 12 paths
(assuming 7 hashes per path) will have power-of-2 sized Bloom filters
(64 or 128 bits), and that is a lot of commits.

> The incremental commit-graph can actually save us here

Oh, I haven't thought of that

> >> +      Bloom filters from commit 0 to commit i (inclusive) in lexicographic
> >> +      order. The Bloom filter for the i-th commit spans from BIDX[i-1] to
> >> +      BIDX[i] (plus header length), where BIDX[-1] is 0.
> >> +    * The BIDX chunk is ignored if the BDAT chunk is not present.
> >> +
> >> +  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
> >> +    * It starts with header consisting of three unsigned 32-bit integers:
> >> +      - Version of the hash algorithm being used. We currently only support
> >> +	value 1 which corresponds to the 32-bit version of the murmur3 hash
> >> +	implemented exactly as described in
> >> +	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
> >> +	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
> >> +	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
> >> +	in Probabilistic Verification"
> > 
> > How should double hashing compute the k hashes, i.e. using 64 bit or
> > 32 bit unsigned integer arithmetic?

Note that this should be clarified in the specs.

> >> +      - The number of times a path is hashed and hence the number of bit positions
> >> +	      that cumulatively determine whether a file is present in the commit.
> >> +      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
> >> +	      contains 'n' entries, then the filter size is the minimum number of 64-bit
> >> +	      words that contain n*b bits.
> > 
> > Since the ideal number of bits per element depends only on the number
> > of hashes per path (k / ln(2) ≈ k * 10 / 7), why is this value stored
> > in the commit-graph?
> 
> The ideal number depends also on what false-positive rate you want.

Well, yes, but indirectly:  according to Wikipedia :) the optimal
number of hashes per element depends only on the desired false
probability, and the optimal number of bits per element depends only
on the number of hashes per element.

So storing the min number of bits per entry seems to be redundant.

> In a
> hypothetical future where we want to allow customization here, we want
> the filters to be consistently sized across all filters.

Wouldn't customizing through the number of hashes be sufficient?

> >> +    * Note: Commits with no changes or more than 512 changes have Bloom filters
> >> +      of length zero.
> > 
> > What does this "Note:" prefix mean in the file format specification?
> > 
> > Can an implementation use a one byte Bloom filter with no bits set for
> > a commit with no changes?  Can an implementation still store a Bloom
> > filter for commits that modify more than 512 paths?
> 
> This is currently due to a hard-coded value in the implementation. It's not a
> requirement of the file format.

Should an implementation detail like that be part of the specs?  It
sure caused a bit of confusion here.

Patch
diff mbox series

diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
index a4f17441aed..de56f9f1efd 100644
--- a/Documentation/technical/commit-graph-format.txt
+++ b/Documentation/technical/commit-graph-format.txt
@@ -17,6 +17,9 @@  metadata, including:
 - The parents of the commit, stored using positional references within
   the graph file.
 
+- The Bloom filter of the commit carrying the paths that were changed between
+  the commit and its first parent, if requested.
+
 These positional references are stored as unsigned 32-bit integers
 corresponding to the array position within the list of commit OIDs. Due
 to some special constants we use to track parents, we can store at most
@@ -93,6 +96,33 @@  CHUNK DATA:
       positions for the parents until reaching a value with the most-significant
       bit on. The other bits correspond to the position of the last parent.
 
+  Bloom Filter Index (ID: {'B', 'I', 'D', 'X'}) (N * 4 bytes) [Optional]
+    * The ith entry, BIDX[i], stores the number of 8-byte word blocks in all
+      Bloom filters from commit 0 to commit i (inclusive) in lexicographic
+      order. The Bloom filter for the i-th commit spans from BIDX[i-1] to
+      BIDX[i] (plus header length), where BIDX[-1] is 0.
+    * The BIDX chunk is ignored if the BDAT chunk is not present.
+
+  Bloom Filter Data (ID: {'B', 'D', 'A', 'T'}) [Optional]
+    * It starts with header consisting of three unsigned 32-bit integers:
+      - Version of the hash algorithm being used. We currently only support
+	value 1 which corresponds to the 32-bit version of the murmur3 hash
+	implemented exactly as described in
+	https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double
+	hashing technique using seed values 0x293ae76f and 0x7e646e2 as
+	described in https://doi.org/10.1007/978-3-540-30494-4_26 "Bloom Filters
+	in Probabilistic Verification"
+      - The number of times a path is hashed and hence the number of bit positions
+	      that cumulatively determine whether a file is present in the commit.
+      - The minimum number of bits 'b' per entry in the Bloom filter. If the filter
+	      contains 'n' entries, then the filter size is the minimum number of 64-bit
+	      words that contain n*b bits.
+    * The rest of the chunk is the concatenation of all the computed Bloom
+      filters for the commits in lexicographic order.
+    * Note: Commits with no changes or more than 512 changes have Bloom filters
+      of length zero.
+    * The BDAT chunk is present if and only if BIDX is present.
+
   Base Graphs List (ID: {'B', 'A', 'S', 'E'}) [Optional]
       This list of H-byte hashes describe a set of B commit-graph files that
       form a commit-graph chain. The graph position for the ith commit in this
diff --git a/commit-graph.c b/commit-graph.c
index 732c81fa1b2..a8b6b5cca5d 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -24,8 +24,10 @@ 
 #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
 #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
 #define GRAPH_CHUNKID_EXTRAEDGES 0x45444745 /* "EDGE" */
+#define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */
+#define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */
 #define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */
-#define MAX_NUM_CHUNKS 5
+#define MAX_NUM_CHUNKS 7
 
 #define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16)
 
@@ -319,6 +321,32 @@  struct commit_graph *parse_commit_graph(void *graph_map, int fd,
 				chunk_repeated = 1;
 			else
 				graph->chunk_base_graphs = data + chunk_offset;
+			break;
+
+		case GRAPH_CHUNKID_BLOOMINDEXES:
+			if (graph->chunk_bloom_indexes)
+				chunk_repeated = 1;
+			else
+				graph->chunk_bloom_indexes = data + chunk_offset;
+			break;
+
+		case GRAPH_CHUNKID_BLOOMDATA:
+			if (graph->chunk_bloom_data)
+				chunk_repeated = 1;
+			else {
+				uint32_t hash_version;
+				graph->chunk_bloom_data = data + chunk_offset;
+				hash_version = get_be32(data + chunk_offset);
+
+				if (hash_version != 1)
+					break;
+
+				graph->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
+				graph->bloom_filter_settings->hash_version = hash_version;
+				graph->bloom_filter_settings->num_hashes = get_be32(data + chunk_offset + 4);
+				graph->bloom_filter_settings->bits_per_entry = get_be32(data + chunk_offset + 8);
+			}
+			break;
 		}
 
 		if (chunk_repeated) {
@@ -337,6 +365,15 @@  struct commit_graph *parse_commit_graph(void *graph_map, int fd,
 		last_chunk_offset = chunk_offset;
 	}
 
+	if (graph->chunk_bloom_indexes && graph->chunk_bloom_data) {
+		init_bloom_filters();
+	} else {
+		/* We need both the bloom chunks to exist together. Else ignore the data */
+		graph->chunk_bloom_indexes = NULL;
+		graph->chunk_bloom_data = NULL;
+		graph->bloom_filter_settings = NULL;
+	}
+
 	hashcpy(graph->oid.hash, graph->data + graph->data_len - graph->hash_len);
 
 	if (verify_commit_graph_lite(graph)) {
@@ -1034,6 +1071,59 @@  static void write_graph_chunk_extra_edges(struct hashfile *f,
 	}
 }
 
+static void write_graph_chunk_bloom_indexes(struct hashfile *f,
+					    struct write_commit_graph_context *ctx)
+{
+	struct commit **list = ctx->commits.list;
+	struct commit **last = ctx->commits.list + ctx->commits.nr;
+	uint32_t cur_pos = 0;
+	struct progress *progress = NULL;
+	int i = 0;
+
+	if (ctx->report_progress)
+		progress = start_delayed_progress(
+			_("Writing changed paths Bloom filters index"),
+			ctx->commits.nr);
+
+	while (list < last) {
+		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
+		cur_pos += filter->len;
+		display_progress(progress, ++i);
+		hashwrite_be32(f, cur_pos);
+		list++;
+	}
+
+	stop_progress(&progress);
+}
+
+static void write_graph_chunk_bloom_data(struct hashfile *f,
+					 struct write_commit_graph_context *ctx,
+					 const struct bloom_filter_settings *settings)
+{
+	struct commit **list = ctx->commits.list;
+	struct commit **last = ctx->commits.list + ctx->commits.nr;
+	struct progress *progress = NULL;
+	int i = 0;
+
+	if (ctx->report_progress)
+		progress = start_delayed_progress(
+			_("Writing changed paths Bloom filters data"),
+			ctx->commits.nr);
+
+	hashwrite_be32(f, settings->hash_version);
+	hashwrite_be32(f, settings->num_hashes);
+	hashwrite_be32(f, settings->bits_per_entry);
+
+	while (list < last) {
+		struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
+		display_progress(progress, ++i);
+		hashwrite(f, filter->data, filter->len * sizeof(unsigned char));
+		list++;
+	}
+
+	stop_progress(&progress);
+}
+
 static int oid_compare(const void *_a, const void *_b)
 {
 	const struct object_id *a = (const struct object_id *)_a;
@@ -1438,6 +1528,7 @@  static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	struct strbuf progress_title = STRBUF_INIT;
 	int num_chunks = 3;
 	struct object_id file_hash;
+	const struct bloom_filter_settings bloom_settings = DEFAULT_BLOOM_FILTER_SETTINGS;
 
 	if (ctx->split) {
 		struct strbuf tmp_file = STRBUF_INIT;
@@ -1482,6 +1573,12 @@  static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		chunk_ids[num_chunks] = GRAPH_CHUNKID_EXTRAEDGES;
 		num_chunks++;
 	}
+	if (ctx->changed_paths) {
+		chunk_ids[num_chunks] = GRAPH_CHUNKID_BLOOMINDEXES;
+		num_chunks++;
+		chunk_ids[num_chunks] = GRAPH_CHUNKID_BLOOMDATA;
+		num_chunks++;
+	}
 	if (ctx->num_commit_graphs_after > 1) {
 		chunk_ids[num_chunks] = GRAPH_CHUNKID_BASE;
 		num_chunks++;
@@ -1500,6 +1597,15 @@  static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 						4 * ctx->num_extra_edges;
 		num_chunks++;
 	}
+	if (ctx->changed_paths) {
+		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+						sizeof(uint32_t) * ctx->commits.nr;
+		num_chunks++;
+
+		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
+						sizeof(uint32_t) * 3 + ctx->total_bloom_filter_data_size;
+		num_chunks++;
+	}
 	if (ctx->num_commit_graphs_after > 1) {
 		chunk_offsets[num_chunks + 1] = chunk_offsets[num_chunks] +
 						hashsz * (ctx->num_commit_graphs_after - 1);
@@ -1537,6 +1643,10 @@  static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	write_graph_chunk_data(f, hashsz, ctx);
 	if (ctx->num_extra_edges)
 		write_graph_chunk_extra_edges(f, ctx);
+	if (ctx->changed_paths) {
+		write_graph_chunk_bloom_indexes(f, ctx);
+		write_graph_chunk_bloom_data(f, ctx, &bloom_settings);
+	}
 	if (ctx->num_commit_graphs_after > 1 &&
 	    write_graph_chunk_base(f, ctx)) {
 		return -1;
@@ -2184,6 +2294,7 @@  void free_commit_graph(struct commit_graph *g)
 		close(g->graph_fd);
 	}
 	free(g->filename);
+	free(g->bloom_filter_settings);
 	free(g);
 }
 
diff --git a/commit-graph.h b/commit-graph.h
index 86be81219da..8e7a8e0e5b2 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -11,6 +11,7 @@ 
 #define GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD "GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD"
 
 struct commit;
+struct bloom_filter_settings;
 
 char *get_commit_graph_filename(struct object_directory *odb);
 int open_commit_graph(const char *graph_file, int *fd, struct stat *st);
@@ -59,6 +60,10 @@  struct commit_graph {
 	const unsigned char *chunk_commit_data;
 	const unsigned char *chunk_extra_edges;
 	const unsigned char *chunk_base_graphs;
+	const unsigned char *chunk_bloom_indexes;
+	const unsigned char *chunk_bloom_data;
+
+	struct bloom_filter_settings *bloom_filter_settings;
 };
 
 struct commit_graph *load_commit_graph_one_fd_st(int fd, struct stat *st,