HTTP2: Huffman decoding implementation is inefficient

[geoffkizer]

We are currently implementing Huffman decoding by looping over a table with a list of encoded values for each length. (See Huffman.cs)

This doesn't seem particularly efficient.

Instead, we should implement Huffman decoding by doing table lookups, using keys of 8 bits or something along those lines.

Note that Huffman encoding from servers seems to be pretty common, so this may have real-world perf impact. (Or maybe not... as always, measuring is the best way to know.)

[jbhensley]

@grant-d Nevermind, I got it worked out now. Sorry for the confusion.

[grant-d]

@jbhensley I fixed a bug in my changes to Array - it wasn't passing all units. Also a couple more optimizations on your code. Fixes pushed to my fork.

  Method |     Mean |     Error |    StdDev | Scaled | ScaledSD | Allocated |
-------- |---------:|----------:|----------:|-------:|---------:|----------:|
    Jump | 619.8 ns | 12.096 ns | 19.185 ns |   0.71 |     0.02 |       0 B |
 OrigOpt | 736.1 ns | 10.946 ns |  9.141 ns |   0.84 |     0.01 |       0 B |
    Orig | 876.1 ns |  3.694 ns |  3.275 ns |   1.00 |     0.00 |       0 B |
   Array | 472.2 ns |  4.820 ns |  4.025 ns |   0.54 |     0.00 |       0 B |

[jcdickinson]

@geoffkizer @jbhensley

You don't need to use s_encodingTable here at all. Just put the bitLength into the decoding table and you can just do one lookup on it.

I tried that, it somehow ended up being slower.

[grant-d]

@jbhensley I have submitted a PR to your repo. Perf is now 0.47, and all units pass.

[jbhensley]

Awesome. I'm working on refactoring both Decode overloads into one, but will probably have to pick it back up after the holiday weekend.

[geoffkizer]

I tried that, it somehow ended up being slower.

I'm surprised by that. Can you post the code?

[danmoseley]

I'm enjoying following this but I'm curious @geoffkizer whether you expect time spent in this code to be material to real scenarios?

[jbhensley]

@geoffkizer In addition to your comments regarding this section:

while (i < count)
            {
                uint next = (uint)(src[i] << 24 + lastDecodedBits);
                next |= (i + 1 < src.Length ? (uint)(src[i + 1] << 16 + lastDecodedBits) : 0);
                next |= (i + 2 < src.Length ? (uint)(src[i + 2] << 8 + lastDecodedBits) : 0);
                next |= (i + 3 < src.Length ? (uint)(src[i + 3] << lastDecodedBits) : 0);

There's another issue to address. If the caller passes in a count less than the source buffer size, this code may read from bytes that it's not technically supposed to. If the caller passes in some arbitrarily large buffer with a count of 2, I assume we should honor that and not load from bytes i + 2 and i + 3.

[jbhensley]

@danmosemsft I can't speak for @geoffkizer, but our efforts appear to be turning up flaws in the current implementation logic, aside from the perf aspect. See my immediately preceding comment

[geoffkizer]

@danmosemsft There's some reason to believe it could matter, but I really don't know if it does matter in real scenarios. Our HTTP2 implementation is not ready for real perf analysis.

[geoffkizer]

@jbhensley

If the caller passes in a count less than the source buffer size, this code may read from bytes that it's not technically supposed to.

Yeah, good catch! It seems like it would be better to use Span here. That would both simplify the code a bit and enforce the bounds.

[jbhensley]

Ok, I have implemented a unified Decode that integrates both overloads. Check it out in the test project here.

I believe that I have eliminated all of the issues we were discussing. My initial objective was creating something that worked correctly and was easy (as possible) to understand. After that, I tried to eliminate a few variables and clean up. Also tried to include enough comments to help the next guy looking at it because this can be a bit difficult to follow.

The decoding array is being built with a Lazy<T> right now, but that can be easily changed to a collection initializer.

Also, I added a test that loops 1 million times. Each pass, it generates an array of bytes of random length up to 255. It populates the bytes with random values, encodes them, decodes them and verifies that you get back with you put in. Figured that might help us turn up oddball combinations/edge cases.

Tests still needed to ensure it handles invalid inputs correctly.

[jbhensley]

@geoffkizer Your thoughts on the rewrite and how far we should go trying to micro-optimize this? In the trade-off between optimization and readability/maintainability and I tend to error on the side of maintainability unless there's a proven reason to go otherwise. Also, is there any concern for the amount of memory we're using for the decoding array? Maybe put it up as a formal PR to enlist more feedback?

[grant-d]

@jbhensley can you maybe make that a ReadOnlySpan<byte> instead - it's more intentional.

Also, maybe use short[,] instead of int[,] - gets us down to ~7.5k runtime overhead (still a concern)

Can you remove the Lazy property (s_decodingArray) entirely and evaluate it just outside the loop in both method bodies instead.

var decodingArray = s_decodingArrayLoader.Value; // <-- Cache Lazy.Value
var srcSpan = new ReadOnlySpan<byte>(src, offset, count); // <--- Note RoS
    ...
    while (sourceIndex < srcSpan.Length)
    {
        ...
        var decodedValue = decodingArray[arrayIndex, workingByte]; // <--- Note cached Lazy.Value

The latter changes gets us down to 0.36 from from 0.43, which is close to be a 3x improvement!

Now:

 Method |     Mean |    Error |   StdDev | Scaled | Allocated |
------- |---------:|---------:|---------:|-------:|----------:|
   Orig | 904.3 ns | 7.200 ns | 6.012 ns |   1.00 |       0 B |
  Array | 322.0 ns | 2.072 ns | 1.837 ns |   0.36 |       0 B |

Was:

  Method |     Mean |     Error |    StdDev | Scaled | ScaledSD | Allocated |
-------- |---------:|----------:|----------:|-------:|---------:|----------:|
    Orig | 880.9 ns | 12.820 ns | 11.365 ns |   1.00 |     0.00 |       0 B |
   Array | 378.2 ns |  2.610 ns |  2.441 ns |   0.43 |     0.01 |       0 B |

[jbhensley]

Awesome work @grant-d. Big gains for simple changes. I'll incorporate this and update.

[grant-d]

No problem. Another small change.

for (int i = 0; i < 4; i++)
{
     uint workingByte = data >> (8 * (3 - i)) & 0xFF; // 24, 16, 8, 0

can be expressed more succinctly (& without the mult) as

for (byte i = 24; i >= 0; i -= 8) // 24, 16, 8, 0
{
    uint workingByte = data >> i & 0xFF;

Similar change on the other override's loop

[geoffkizer]

Your thoughts on the rewrite and how far we should go trying to micro-optimize this? In the trade-off between optimization and readability/maintainability and I tend to error on the side of maintainability unless there's a proven reason to go otherwise.

Readability and maintainability are critical.

As mentioned above, we don't really know how much of an impact Huffman decoding perf has in real world scenarios. As such, micro-optimization doesn't make sense right now. The focus should be on changes that make the code obviously better (for perf or correctness) without introducing additional complexity.

We can always revisit and micro-optimize later, if we get data that shows it's worth it.

[grant-d]

@geoffkizer what about the 7.5k static runtime table size. It seems a lot for a deep internal component

[grant-d]

As an aside, it's debatable whether maintainability is affected by unrolling here. This code:

for (var i = 0; i < 4; i++)
{
    <stuff>
}

becomes this:

for (var i = 0; i < 4; i++)
{
    Refactored(i, ...);
}

[AggressiveInline]
private static Refactored(int i, …) => <stuff>;

becomes this:

Refactored(0, ...);
Refactored(1, ...);
Refactored(2, ...);
Refactored(3, ...);

[AggressiveInline]
private static Refactored(int i, …) => <stuff>;

That being said, I do agree that it's premature to do this right now.

[jbhensley]

Just to be clear, the Decode method as it currently stands is below in full. There is only one now, although a separate overload still exists in the test project.

I also share the concern regarding memory consumption. We can cut that in half by changing the decoding table to a byte array (currently is a short array), but that requires a separate lookup from the encoding table to get the bit length since byte is not big enough to carry both the decoded value and bit length in one.

Other than that, it feels like we are at the end of this. Anything else or should we offer up a PR?

public static int Decode(byte[] src, int offset, int count, byte[] dst)
{
    // input validation
    if (src == null || count == 0)
        return 0;

    if (offset < 0)
        throw new ArgumentOutOfRangeException(nameof(offset));
    if (offset >= src.Length)
        throw new ArgumentOutOfRangeException(nameof(offset));
    if (count < 0)
        throw new ArgumentOutOfRangeException(nameof(count));
    if (count > src.Length - offset)
        throw new ArgumentOutOfRangeException(nameof(count));
    if (dst == null)
        throw new ArgumentNullException(nameof(dst));

    // let's narrow thing down to just the part of the source buffer that we've been asked to decode
    var sourceSpan = new ReadOnlySpan<byte>(src, offset, count);
    int sourceIndex = 0;
    int destinationIndex = 0;
    int bitOffset = 0;              // symbol bit patterns do not necessarily align to byte boundaries. need to keep track of our offset within a byte
    var decodingArray = s_decodingArrayLoader.Value;
    while (sourceIndex < sourceSpan.Length)
    {   
        int arrayIndex = 0;         // index into the decoding array
        int decodedBits = 0;

        // decoding a symbol will take a maximum of four bytes (longest symbol is represented by a 30 bit pattern)
        for (int i = 0; i <= 24; i += 8)
        {
            // grab the next byte and push it over to make room for bits we have to borrow
            byte workingByte = (byte)(sourceSpan[sourceIndex] << bitOffset);
            // borrow some bits if we need to
            if (bitOffset > 0)
                workingByte |= (byte)((sourceIndex < sourceSpan.Length - 1 ? sourceSpan[sourceIndex + 1] : 0) >> (8 - bitOffset));

            // key into array
            int decodedValue = decodingArray[arrayIndex, workingByte];

            // negative values are a pointer to the next decoding array
            if (decodedValue < 0)
            {
                // move to the next source byte and prepare to key in again
                sourceIndex++;
                arrayIndex = -decodedValue;
            }
            else
            // we have decoded a character
            {
                decodedBits = decodedValue >> 8;    // length is in the second LSB
                decodedValue &= 0xFF;               // value is in the LSB

                // Destination is too small.
                if (destinationIndex == dst.Length)
                    throw new HuffmanDecodingException();

                // store the decoded value and increment destinationIndex
                dst[destinationIndex++] = (byte)decodedValue;

                // if we decoded more bits than we are borrowing then advance to next byte
                if (decodedBits - i >= 8 - bitOffset)
                    sourceIndex++;

                // calculate and re-align bitOffset
                bitOffset += decodedBits;
                bitOffset &= 7; // same as modulo 8

                break;
            }
        }

        // we checked four bytes did not come up with a valid bit pattern
        if (decodedBits == 0)
            throw new HuffmanDecodingException();

        // check for padding in the last byte before we loop back around and try to decode again
        if (sourceIndex == sourceSpan.Length - 1)
        {

            // see if all of the remaning bits are padding
            int paddingMask = (0x1 << (8 - bitOffset)) - 1;
            if ((sourceSpan[sourceIndex] & paddingMask) == paddingMask)
            {
                // if our bitOffset is zero then all of bits in this byte are set
                // "A padding strictly longer than 7 bits MUST be treated as a decoding error."
                // https://httpwg.org/specs/rfc7541.html#rfc.section.5.2
                if (bitOffset == 0)
                    throw new HuffmanDecodingException();

                // otherwise (padding less than 8), just break out of the main loop because we are done
                break;
            }
        }
    }

    return destinationIndex;    // destinationIndex is incremented each time a value is decoded, so it also represents total decoded byte count
}

[grant-d]

Thanks for checking. Only one small change - could you expand the 2nd line here into a full nested if instead. It's hard to parse, which makes maintaining and understanding it hard, especially since only the true case does anything useful.

if (bitOffset > 0)
    workingByte |= (byte)((sourceIndex < sourceSpan.Length - 1 ? sourceSpan[sourceIndex + 1] : 0) >> (8 - bitOffset));

[danmoseley]

I don't see the link to the PR (?) but I noticed this code above (maybe not yours)

    if (offset < 0)
        throw new ArgumentOutOfRangeException(nameof(offset));
    if (offset >= src.Length)
        throw new ArgumentOutOfRangeException(nameof(offset));
    if (count < 0)
        throw new ArgumentOutOfRangeException(nameof(count));
    if (count > src.Length - offset)
        throw new ArgumentOutOfRangeException(nameof(count));

The compiler and JIT do not coalesce these exceptions. It is less code if you write eg

    if (offset < 0 || offset >= src.Length || count < 0 || count > src.Length - offset)
        throw new ArgumentOutOfRangeException(nameof(count));

I see more of this pattern.

Also, many places we cast to uint to combine comparisons, eg., change if (offset < 0 || offset >= src.Length || count < 0 || count > src.Length - offset) to if ((uint)offset >= (uint)src.Length || (uint)count > (uint)(src.Length - offset))

[saucecontrol]

Since src.Length can't be negative, you can eliminate two of the compares using this pattern

if ((uint)offset >= (uint)src.Length)
    throw new ArgumentOutOfRangeException(nameof(offset));
if ((uint)count > (uint)(src.Length - offset))
    throw new ArgumentOutOfRangeException(nameof(count));

[jbhensley]

Thanks @danmosemsft and @saucecontrol, The PR is up here.

[danmoseley]

@AndyAyersMS is there already an issue for the JIT to do the "uint cast" trick above for free? It seems like the pattern would be fairly consistent (and so hopefully easy to recognize) - like offset < 0 || offset >= src.Length

[geoffkizer]

what about the 7.5k static runtime table size

This isn't a problem if it's needed, but it would be good to understand why the table is so large and whether it actually needs to be that large.

[AndyAyersMS]

dotnet/coreclr#16363

[geoffkizer]

To step back here for a minute:

There have been a lot of issues discussed above. I think these fall into the following categories:

(1) Correctness. This is the most important. I have a PR out for one correctness issue here: dotnet/corefx#32043. This PR includes a bunch of unit tests as well. Any additional changes will need to merge with this PR and pass the new tests.

Beyond that, there's at least one other correctness issue I'm aware of -- reading past count. This needs to get fixed as well. My suggestion here is to change Decode so it takes a ReadOnlySpan<byte>, which effectively makes it impossible to read beyond the end of the span.

Are there other correctness issues that were identified that I missed?

(2) Incremental perf improvements. There was some discussion of small changes that make the existing code better and would apply regardless of the actual decoding algorithm. I'm not sure what happened with these? If there are any changes that make sense here, we should make them before making big algorithmic changes. This ensures we have a reasonable baseline for comparing the different algorithmic approaches.

(3) Algorithmic changes. I think we've got some good data about the different approaches, but I don't know quite where all of this ended up. We need to understand the different choices here and the tradeoffs involved (e.g. added memory usage, table construction costs, etc).

Also, it would be good to get the benchmarking code added to the repo. This will be useful in the future to validate we are not regressing and to evaluate any future changes here.

[geoffkizer]

Additionally:

The tests I added in the PR linked above are reasonably comprehensive, but they are missing some invalid cases. In particular, we need to generate all cases of a truncated encoding and ensure that the decoder correctly rejects these cases.

[grant-d]

(2) - I optimized the original code, here's the results (0.84). Do you want me to send a separate PR for that?

  Method |     Mean |     Error |    StdDev | Scaled | ScaledSD | Allocated |
-------- |---------:|----------:|----------:|-------:|---------:|----------:|
 CodeOpt | 736.1 ns | 10.946 ns |  9.141 ns |   0.84 |     0.01 |       0 B |
    Orig | 876.1 ns |  3.694 ns |  3.275 ns |   1.00 |     0.00 |       0 B |

[jbhensley]

I agree that correctness can be fixed aside from any algorithmic change. Unit tests from dotnet/corefx#32043 have been incorporated and are passing. I'll be updating the PR shortly. There was one correction to the code that the tests turned up for invalid inputs.

For perf, it looks like @grant-d has managed to get the original code to scale at 0.84 as per above. The last test with the array method is at 0.36 as per here.

I'm not sure how we attempt to answer whether the trade-off of memory for speed is worth it in this scenario.

[geoffkizer]

Before we take any PR that changes the algorithm here, we need to do a few things:

(1) Ensure we have comprehensive tests. My PR has a bunch of tests, and I think they are reasonably comprehensive for valid cases. But we need more comprehensive testing of invalid cases. This includes (a) incomplete final bit sequences and (b) EOS appearing anywhere in the encoding. I think that covers all the possible invalid sequences.

(2) Submit a PR for the benchmark code. We should review the code and ensure it's measuring useful things, and we should get it in the repo so that we can use it to validate future changes here.

[jbhensley]

I can work on that. Hopefully have something before Monday.

[geoffkizer]

One other thought on the algorithmic approach here:

The "jump" algorithm that @jcdickinson posted above could be modified to process more than a single bit at a time. In particular, 4 bits seems like a reasonable number to process in a single operation. This would require 16 different transitions per starting state (versus 2 for a single bit), and since there are 256 starting states, this is probably reasonable in terms of table size.

Since the minimum encoding size is 5 bits, there can be at most one decoded value emitted for every 4 bits walked, so for each transition we need to know (a) what the final tree state is after walking the 4 bits, and (b) whether a symbol was emitted or not.

[jbhensley]

Maybe @jcdickinson and/or @grant-d can work on further optimization of the "jump" method.

I submitted PR dotnet/corefx#32190, which adds a test for emitting EOS in the middle of an otherwise valid sequence.

As for dotnet/corefx#32124, I feel like we should just close this one out as it's not clear at the moment which direction this is going to go and the open PR is probably just tying up other resources.

[jcdickinson]

@jbhensley @geoffkizer I'm happy to attempt improvements on "jump" (really a DFA) to work over nibbles or bytes if there is interest in optimizing this further.

[geoffkizer]

@jcdickinson I think that would be interesting to try, yeah. I would guess that nibbles are the sweet spot; doing bytes seems like it would result in a really large table.

[kirsty14141]

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---

From: Geoff Kizer notifications@github.com Sent: Monday, September 10, 2018 11:52 pm To: dotnet/corefx Cc: Subscribed Subject: Re: [dotnet/corefx] HTTP2: Huffman decoding implementation is inefficient (#31751)

@jcdickinsonhttps://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fjcdickinson&data=02%7C01%7C%7Cb45b18da0763435fae1f08d617701047%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636722167400812366&sdata=wA86TdkooSDhY2a8MZ8INFZZdDB53AA%2F08TlSB2qqfM%3D&reserved=0 I think that would be interesting to try, yeah. I would guess that nibbles are the sweet spot; doing bytes seems like it would result in a really large table.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fdotnet%2Fcorefx%2Fissues%2F31751%23issuecomment-420087149&data=02%7C01%7C%7Cb45b18da0763435fae1f08d617701047%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636722167400812366&sdata=oy%2FqDfvWbCOfzWULDyF8C4veMueSgGgVqPc3Vf6hoRo%3D&reserved=0, or mute the threadhttps://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fnotifications%2Funsubscribe-auth%2FAdM6-KTNq21ZY6d3iuEFJTJBF0yBYijUks5uZu0igaJpZM4V7jpR&data=02%7C01%7C%7Cb45b18da0763435fae1f08d617701047%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636722167400812366&sdata=f0SNsMoz968YdbD2vg7j0ztao9UGYrE%2Bi%2F2vdlhXtYo%3D&reserved=0.

name,address,icon,phone,website,userComment,lat,lng,tags,gid,4id "Keely Rafferty Makeup","Portishead House, 29 Nore Rd, Portishead, Bristol BS20 8NN, UK","generic","+44 7734 241255","http://www.keelyrafferty.com/","","51.485311","-2.767996","Https://goo.gl/photos/pMYTnCir","ChIJp1MULPzxcUgRp2Nahs9vnz0" "Location D'Outils Gps Inc","1282 Av de la Gare, Mascouche, QC, J7K, Canada","generic","+1 (450) 417-1477","","","45.740653","-73.589199","Contacts","" "Dan Freeman","26 Cobley Croft, Clevedon, United Kingdom","generic","+447538552769","","","51.482252","-2.787124","Contacts","" "Location D'Outils Gps Inc","1282 Av de la Gare, Mascouche, QC, J7K, Canada","generic","+1 (450) 417-1477","","","45.740653","-73.589199","Contacts","" "United Kingdom","United Kingdom","civic","","","","52.80110090809378","-1.636962890625","Likes","ChIJM8zfqhnwdUgRMXaz0VNl3ow" "Tyntesfield House (NT)","Clevedon Rd (near Wraxall Hill), Bristol, BS48 1NT, United Kingdom","generic","+44 344 800 4966","http://www.nationaltrust.org.uk/tyntesfield/","","51.44182619999999","-2.718278599999999","Likes","ChIJYTkuzCDzcUgRsnkpeIdf8oI" "United Kingdom","United Kingdom","civic","","","","52.80110090809378","-1.636962890625","Checkins","ChIJM8zfqhnwdUgRMXaz0VNl3ow" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","Checkins#Https://assets.contentstack.io","ChIJS215oIntcUgRPZbO7CuAaec" "Vue Cinema","Patchway, Bristol BS10 7SR, UK","movies","+44 871 224 0240","http://www.myvue.com","","51.52343949999999","-2.6040692","Checkins#Https://assets.contentstack.io","ChIJUYB5xIORcUgRBzedC4CSmiw" "Burger King","The Venue, Merlin Rd, Patchway, Bristol BS10 7SR, UK","restaurant","+44 117 959 0712","http://www.burgerking.co.uk/","","51.52345959999999","-2.6010024","Checkins#Https://assets.contentstack.io","ChIJIV0CBsiRcUgR8wwBC_4vHVU" "Mark's Barbershop","3A West Hill Bristol England BS20 6PG United Kingdom","generic","","","","51.4816660944565","-2.782440790723976","Checkins#Https://assets.contentstack.io","" "Little Harp","Elton Rd, Clevedon BS21 7RH, UK","bar","+44 1275 343739","https://www.oldenglishinns.co.uk/our-locations/the-little-harp-clevedon","","51.4373958","-2.865220799999999","Checkins#Https://assets.contentstack.io","ChIJlbwvRfXwcUgR2CkZghuzo30" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","Checkins#Https://assets.contentstack.io","ChIJS215oIntcUgRPZbO7CuAaec" "Clevedon Seafront","The Beach Clevedon North Somerset","generic","","","","51.436309265421464","-2.865371091919184","Checkins#Https://assets.contentstack.io","" "Mark's Barbershop","3A West Hill Bristol England BS20 6PG United Kingdom","generic","","","","51.4816660944565","-2.782440790723976","Checkins#Https://assets.contentstack.io","" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","Checkins#Https://assets.contentstack.io","ChIJHaSp8ontcUgRM0wmUgMp6l0" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","Checkins#Https://assets.contentstack.io","ChIJS215oIntcUgRPZbO7CuAaec" "Mark's Barbershop","3A West Hill Bristol England BS20 6PG United Kingdom","generic","","","","51.4816660944565","-2.782440790723976","Checkins#Https://assets.contentstack.io","" "The Albion","15 Bristol Rd. Portishead North Somerset BS20 6PZ","generic","","","","51.47631195397998","-2.7668539197926587","Checkins#Https://assets.contentstack.io","" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","Checkins#Https://assets.contentstack.io","ChIJS215oIntcUgRPZbO7CuAaec" "Mark's Barbershop","3A West Hill Bristol England BS20 6PG United Kingdom","generic","","","","51.4816660944565","-2.782440790723976","Checkins#Https://assets.contentstack.io","" "Mark's Barbershop","3A West Hill Bristol England BS20 6PG United Kingdom","generic","","","","51.4816660944565","-2.782440790723976","Checkins#Https://assets.contentstack.io","" "Clevedon Seafront","The Beach Clevedon North Somerset","generic","","","","51.436309265421464","-2.865371091919184","Likes","" "Little Harp","Elton Rd, Clevedon BS21 7RH, UK","bar","+44 1275 343739","https://www.oldenglishinns.co.uk/our-locations/the-little-harp-clevedon","","51.4373958","-2.865220799999999","Likes","ChIJlbwvRfXwcUgR2CkZghuzo30" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","Likes","ChIJHaSp8ontcUgRM0wmUgMp6l0" "Lidl","Harbour Rd, Portishead, Bristol BS20 7DE, UK","shopping","+44 800 977 7766","http://www.lidl.co.uk/","","51.4858439","-2.7633696","Likes","ChIJEeX3EIntcUgR4EsSxlQvIw8" "Clevedon Seafront","The Beach Clevedon North Somerset","generic","","","","51.436309265421464","-2.865371091919184","What","" "Badminton Villa","10 Upper Oldfield Park Bath Bath and North East Somerset BA2 3JZ","generic","","","","51.375799700792406","-2.370470520619507","Checkins","" "Sainsbury's","Serbert Rd, Portishead, Bristol BS20 7GD, UK","shopping","+44 1275 750400","https://stores.sainsburys.co.uk/2252/portishead","","51.4839614","-2.7613376","Checkins","ChIJrUeuNojtcUgRDg9ZtuAVw80" "The Posset Cup","3, Mustard Way, Portishead BS20 7QZ, UK","bar","+44 1275 848008","https://www.jdwetherspoon.com/pubs/all-pubs/england/somerset/the-posset-cup-portishead","","51.48571630000001","-2.7624962","Checkins","ChIJpehLHYntcUgRE-w5YuDMwmA" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Badminton Villa","10 Upper Oldfield Park Bath Bath and North East Somerset BA2 3JZ","generic","","","","51.375799700792406","-2.370470520619507","What","" "Badminton Villa","10 Upper Oldfield Park Bath Bath and North East Somerset BA2 3JZ","generic","","","","51.375799700792406","-2.370470520619507","36 Hours In...Bath","" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","Checkins","ChIJkVnr2IGRcUgRxhA5pLK7lec" "Asda Patchway Supercentre","Highwood Ln, Patchway, Bristol BS34 5TL, UK","shopping","+44 117 317 2400","http://storelocator.asda.com/store/patchway-supercentre","","51.5306145","-2.597049600000001","Checkins","ChIJL3f-H56RcUgR6l06m6xXMzc" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","Checkins","ChIJkVnr2IGRcUgRxhA5pLK7lec" "Smyths Toys Superstores","5, A, Cribbs Causeway Retail Park, Lysander Rd, Patchway, Bristol BS34 5TX, UK","shopping","+44 117 959 0055","http://www.smythstoys.com/","","51.52624339999999","-2.600264","Checkins","ChIJ8QRHo4CRcUgR5c96odklLJE" "B&M Home Store","3 Centaurus Rd, Patchway, Bristol BS34 5TS, UK","shopping","+44 330 838 9530","https://www.bmstores.co.uk/stores/bristol-patchway-530","","51.5272919","-2.5973424","Checkins","ChIJDVQq7YGRcUgRLa0ly8_ABp0" "McDonald's","Western Links, Weston-super-Mare BS23 3WL, United Kingdom","restaurant","+44 1934 625340","http://www.mcdonalds.co.uk/","","51.3390109","-2.956917499999999","Checkins","ChIJvYjF49D4cUgRoVqxOjGVwlQ" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Smyths Toys Superstores","5, A, Cribbs Causeway Retail Park, Lysander Rd, Patchway, Bristol BS34 5TX, UK","shopping","+44 117 959 0055","http://www.smythstoys.com/","","51.52624339999999","-2.600264","Likes","ChIJ8QRHo4CRcUgR5c96odklLJE" "Asda Patchway Supercentre","Highwood Ln, Patchway, Bristol BS34 5TL, UK","shopping","+44 117 317 2400","http://storelocator.asda.com/store/patchway-supercentre","","51.5306145","-2.597049600000001","Likes","ChIJL3f-H56RcUgR6l06m6xXMzc" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","Likes","ChIJkVnr2IGRcUgRxhA5pLK7lec" "Sainsbury's","Serbert Rd, Portishead, Bristol BS20 7GD, UK","shopping","+44 1275 750400","https://stores.sainsburys.co.uk/2252/portishead","","51.4839614","-2.7613376","","ChIJrUeuNojtcUgRDg9ZtuAVw80" "Lidl","Harbour Rd, Portishead, Bristol BS20 7DE, UK","shopping","+44 800 977 7766","http://www.lidl.co.uk/","","51.4858439","-2.7633696","","ChIJEeX3EIntcUgR4EsSxlQvIw8" "National Trust - Tyntesfield","Wraxall, Tyntesfield BS48 1NX, United Kingdom","generic","+44 344 800 4966","http://www.nationaltrust.org.uk/tyntesfield/","","51.44182619999999","-2.718278599999999","Likes","ChIJYTkuzCDzcUgRsnkpeIdf8oI" "Badminton Villa","10 Upper Oldfield Park Bath Bath and North East Somerset BA2 3JZ","generic","","","","51.375799700792406","-2.370470520619507","","" "The Bath Priory","Weston Rd, Bath BA1 2XT, United Kingdom","lodging","+44 1225 331922","http://www.thebathpriory.co.uk/","","51.3900945","-2.382454000000001","36 Hours In...Bath","ChIJxSy0uEiBcUgRBWDUuWOJVsE" "The Halcyon Hotel Apartments, Henry Street","8 Henry St, Bath BA1 1JT, UK","lodging","+44 1225 585100","http://www.thehalcyon.com/","","51.3799113","-2.3576342","36 Hours In...Bath","ChIJ05aKlhGBcUgRcn9OzuqwEFQ" "Sub13 - new gin collection bar","4 2ee, Edgar Buildings, George St, Bath BA1 2DU, UK","bar","+44 1225 466667","http://www.sub13.net","","51.3849994","-2.3624013","36 Hours In...Bath","ChIJq6q2oRSBcUgRs6kN6clmP80" "The Roman Baths","Stall St, Bath BA1 1LZ, United Kingdom","museum","+44 1225 477785","https://www.romanbaths.co.uk/","","51.381072","-2.359619","36 Hours In...Bath","ChIJtTDV3hOBcUgRTSLxFGi-Rg4" "Colonna & Small's","6 Chapel Row, Bath BA1 1HN, United Kingdom","cafe","+44 7766 808067","http://www.colonnaandsmalls.co.uk/","","51.3827777","-2.3644163","36 Hours In...Bath","ChIJMUKdQBSBcUgRvz8IiqG_Fm8" "The Bertinet Bakery","1 New Bond St Pl, Bath BA1 1BH, United Kingdom","restaurant","+44 1225 445531","http://www.bertinet.com/","","51.3829721","-2.360359700000001","36 Hours In...Bath","ChIJG_nQlxOBcUgRMCvWK8NtvwU" "Bath Assembly Rooms","Bennett St, Bath, Avon BA1 2QH, United Kingdom","generic","+44 1225 477173","http://www.nationaltrust.org.uk/bath-assembly-rooms/","","51.386204","-2.3628429","36 Hours In...Bath","ChIJVyYrVWuBcUgRXqedsmf2zJc" "The Royal Crescent Hotel","16 Royal Crescent, Bath BA1 2LS, United Kingdom","lodging","+44 1225 823333","https://www.royalcrescent.co.uk/?utm_source=google&utm_medium=local&utm_campaign=hotel","","51.387348","-2.368125999999999","36 Hours In...Bath","ChIJZUo6omqBcUgRBxusGzy3GoI" "The Star Inn","The Street Hullavington Wiltshire SN14 6DU","generic","","","","51.536032213209815","-2.1543502807617183","36 Hours In...Bath","" "Thermae Bath Spa","The Hetling Pump Room, Hot Bath St, Bath BA1 1SJ, United Kingdom","generic","+44 1225 331234","http://www.thermaebathspa.com/","","51.3803643","-2.3615092","36 Hours In...Bath","ChIJ7b7VUBGBcUgRI-5CyCMdPsM" "Prior Park Landscape Garden","Ralph Allen Drive Bath Bath and North East Somerset BA2 5AH","generic","","","","51.36479996703179","-2.3475266493227194","36 Hours In...Bath","" "Costcutter","Avon way North Somerset","generic","","","","51.481604736419456","-2.7814604011169495","What","" "Smyths Toys Superstores","5, A, Cribbs Causeway Retail Park, Lysander Rd, Patchway, Bristol BS34 5TX, UK","shopping","+44 117 959 0055","http://www.smythstoys.com/","","51.52624339999999","-2.600264","","ChIJ8QRHo4CRcUgR5c96odklLJE" "Asda Patchway Supercentre","Highwood Ln, Patchway, Bristol BS34 5TL, UK","shopping","+44 117 317 2400","http://storelocator.asda.com/store/patchway-supercentre","","51.5306145","-2.597049600000001","","ChIJL3f-H56RcUgR6l06m6xXMzc" "Smyths Toys Superstores","5, A, Cribbs Causeway Retail Park, Lysander Rd, Patchway, Bristol BS34 5TX, UK","shopping","+44 117 959 0055","http://www.smythstoys.com/","","51.52624339999999","-2.600264","","ChIJ8QRHo4CRcUgR5c96odklLJE" "Asda Patchway Supercentre","Highwood Ln, Patchway, Bristol BS34 5TL, UK","shopping","+44 117 317 2400","http://storelocator.asda.com/store/patchway-supercentre","","51.5306145","-2.597049600000001","","ChIJL3f-H56RcUgR6l06m6xXMzc" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","","ChIJkVnr2IGRcUgRxhA5pLK7lec" "The Posset Cup","3, Mustard Way, Portishead BS20 7QZ, UK","bar","+44 1275 848008","https://www.jdwetherspoon.com/pubs/all-pubs/england/somerset/the-posset-cup-portishead","","51.48571630000001","-2.7624962","","ChIJpehLHYntcUgRE-w5YuDMwmA" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Little Harp","Elton Rd, Clevedon BS21 7RH, UK","bar","+44 1275 343739","https://www.oldenglishinns.co.uk/our-locations/the-little-harp-clevedon","","51.43759530000001","-2.864774","","ChIJlbwvRfXwcUgR2CkZghuzo30" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","","ChIJHaSp8ontcUgRM0wmUgMp6l0" "Lidl","Harbour Rd, Portishead, Bristol BS20 7DE, UK","shopping","+44 800 977 7766","http://www.lidl.co.uk/","","51.4858439","-2.7633696","","ChIJEeX3EIntcUgR4EsSxlQvIw8" "National Trust - Tyntesfield","Wraxall, Tyntesfield BS48 1NX, United Kingdom","generic","+44 344 800 4966","http://www.nationaltrust.org.uk/tyntesfield/","","51.44182619999999","-2.718278599999999","","ChIJYTkuzCDzcUgRsnkpeIdf8oI" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","","ChIJHaSp8ontcUgRM0wmUgMp6l0" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","","ChIJHaSp8ontcUgRM0wmUgMp6l0" "The Posset Cup","3, Mustard Way, Portishead BS20 7QZ, UK","bar","+44 1275 848008","https://www.jdwetherspoon.com/pubs/all-pubs/england/somerset/the-posset-cup-portishead","","51.48571630000001","-2.7624962","","ChIJpehLHYntcUgRE-w5YuDMwmA" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","","ChIJkVnr2IGRcUgRxhA5pLK7lec" "Asda Patchway Supercentre","Highwood Ln, Patchway, Bristol BS34 5TL, UK","shopping","+44 117 317 2400","http://storelocator.asda.com/store/patchway-supercentre","","51.5306145","-2.597049600000001","","ChIJL3f-H56RcUgR6l06m6xXMzc" "Toys R Us","Centaurus Rd, Patchway, Bristol BS34 5TU, UK","shopping","+44 117 959 1430","http://www.toysrus.co.uk/?utm_source=google&utm_medium=local&utm_campaign=gmb%20ToysRUsBristolCribbsCauseway3606","","51.528624","-2.596471","","ChIJkVnr2IGRcUgRxhA5pLK7lec" "Smyths Toys Superstores","5, A, Cribbs Causeway Retail Park, Lysander Rd, Patchway, Bristol BS34 5TX, UK","shopping","+44 117 959 0055","http://www.smythstoys.com/","","51.52624339999999","-2.600264","","ChIJ8QRHo4CRcUgR5c96odklLJE" "B&M Home Store","3 Centaurus Rd, Patchway, Bristol BS34 5TS, UK","shopping","+44 330 838 9530","https://www.bmstores.co.uk/stores/bristol-patchway-530","","51.5272919","-2.5973424","","ChIJDVQq7YGRcUgRLa0ly8_ABp0" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Little Harp","Elton Rd, Clevedon BS21 7RH, UK","bar","+44 1275 343739","https://www.oldenglishinns.co.uk/our-locations/the-little-harp-clevedon","","51.43759530000001","-2.864774","","ChIJlbwvRfXwcUgR2CkZghuzo30" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","","ChIJHaSp8ontcUgRM0wmUgMp6l0" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48688259999999","-2.7653411","","ChIJS215oIntcUgRPZbO7CuAaec" "The Bath Priory","Weston Rd, Bath BA1 2XT, United Kingdom","lodging","+44 1225 331922","http://www.thebathpriory.co.uk/","","51.3900945","-2.382454000000001","","ChIJxSy0uEiBcUgRBWDUuWOJVsE" "The Halcyon Hotel Apartments, Henry Street","8 Henry St, Bath BA1 1JT, UK","lodging","+44 1225 585100","http://www.thehalcyon.com/","","51.3799113","-2.3576342","","ChIJ05aKlhGBcUgRcn9OzuqwEFQ" "Sub13 - new gin collection bar","4 2ee, Edgar Buildings, George St, Bath BA1 2DU, UK","bar","+44 1225 466667","http://www.sub13.net","","51.3849994","-2.3624013","","ChIJq6q2oRSBcUgRs6kN6clmP80" "Colonna & Small's","6 Chapel Row, Bath BA1 1HN, United Kingdom","cafe","+44 7766 808067","http://www.colonnaandsmalls.co.uk/","","51.3827777","-2.3644163","","ChIJMUKdQBSBcUgRvz8IiqG_Fm8" "The Bertinet Bakery","1 New Bond St Pl, Bath BA1 1BH, United Kingdom","restaurant","+44 1225 445531","http://www.bertinet.com/","","51.3829721","-2.360359700000001","","ChIJG_nQlxOBcUgRMCvWK8NtvwU" "The Royal Crescent Hotel","16 Royal Crescent, Bath BA1 2LS, United Kingdom","lodging","+44 1225 823333","https://www.royalcrescent.co.uk/?utm_source=google&utm_medium=local&utm_campaign=hotel","","51.387348","-2.368125999999999","","ChIJZUo6omqBcUgRBxusGzy3GoI" "Thermae Bath Spa","The Hetling Pump Room, Hot Bath St, Bath BA1 1SJ, United Kingdom","generic","+44 1225 331234","http://www.thermaebathspa.com/","","51.3803643","-2.3615092","","ChIJ7b7VUBGBcUgRI-5CyCMdPsM" "Kirsty Martin","Martcombe Road, Bristol, England, BS20, United Kingdom","generic","+44 7453 655952","","","51.474918","-2.70991","Contacts","" "Kirsty Martin","Martcombe Road, Bristol, England, BS20, United Kingdom","generic","+44 7453 655952","","","51.474918","-2.70991","Contacts","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Portishead Working Mens Club","Slade Road, Portishead, BS20 6BW, United Kingdom","generic","","","","51.484703248025","-2.7693352316805","Facebook","" "Royal Victoria Park","Marlborough Ln, Bath BA1 2NQ, UK","generic","+44 1225 394041","http://visitbath.co.uk/things-to-do/royal-victoria-park-p25701","","51.3857067","-2.3708195","Facebook","ChIJNbSuIRWBcUgRDWNdo793S88" "Swindon Oasis","Swindon, United Kingdom","generic","","","","51.48171056","-2.52573798","Facebook","" "Oldbury Court Estate","Oldbury Ct Rd, Fishponds, Bristol BS16 2JH, UK","generic","+44 117 922 2000","https://www.bristol.gov.uk/museums-parks-sports-culture/oldbury-court-estate","","51.48785659999999","-2.529845399999999","Facebook","ChIJb9eUOiCQcUgRrq22DD_ICk8" "Riverside Holiday Village","Bridgwater Rd, Bleadon, Weston-super-Mare BS24 0AN, UK","camping","+44 1934 812342","http://www.westcountryparks.co.uk/riverside-holiday-village/","","51.3069719","-2.9592683","Facebook","ChIJbRYKqW0CckgRixFozu7irpM" "Blaise Castle","Bristol BS10 7QT, UK","generic","+44 117 903 9818","http://www.friendsofblaise.co.uk/","","51.5025659","-2.637383899999999","Facebook","ChIJfdUWIGaScUgRpZyQr13zOTk" "McDonald's","4, Portishead Retail Park, Wyndham Way, Portishead, Bristol, Somerset BS20 7BY, United Kingdom","restaurant","+44 1275 844792","http://www.mcdonalds.co.uk/","","51.4841309","-2.765955","","ChIJHaSp8ontcUgRM0wmUgMp6l0" "High Down Junior School","Down Rd, Portishead, Bristol BS20 6DY, UK","school","+44 1275 843969","http://www.highdownjunior.co.uk/","","51.4801769","-2.7872175","Facebook","ChIJHSDTGQfycUgR1FNO3N3KgWc" "Parish Wharf Leisure Centre","Harbour Rd, Portishead, Bristol BS20 7DD, UK","generic","+44 1275 848494","http://www.placesforpeopleleisure.org/centres/parish-wharf-leisure-centre/","","51.48686459999999","-2.7653641","","ChIJS215oIntcUgRPZbO7CuAaec" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "The Fleece","12 St Thomas St, Bristol BS1 6JJ, UK","generic","+44 117 945 0996","http://www.thefleece.co.uk/","","51.45230189999999","-2.589315399999999","Facebook","ChIJ_TD91XuOcUgRjMrlhE2_y5o" "The Bristol Hot Air Baloon Fiesta","Bristol, BS41 9, United Kingdom","generic","","","","51.441254277308","-2.6433306349142","Facebook","" "Weston-super-Mare","Weston-super-Mare, United Kingdom","generic","","","","51.3458","-2.96778","Facebook","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Brean Leisure Park","Coast Rd, Brean, Burnham-on-Sea TA8 2QY, UK","generic","+44 1278 751595","http://www.brean.com/","","51.2851298","-3.009675","Facebook","ChIJo-wata8BckgRnLpSPWqfLiY" "Brean Leisure Park","Coast Rd, Brean, Burnham-on-Sea TA8 2QY, UK","generic","+44 1278 751595","http://www.brean.com/","","51.2851298","-3.009675","Facebook","ChIJo-wata8BckgRnLpSPWqfLiY" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Portishead, North Somerset","Portishead, United Kingdom","generic","","","","51.4844","-2.77028","Facebook","" "Redcliffe Bay Seafront","249 Down Road Bristol England BS20 8HY United Kingdom","generic","","","","51.476458095","-2.8004557133333","Facebook","" "Weston Big Wood","25 Spring Rise Bristol England BS20 6RE United Kingdom","generic","","","","51.475398524608","-2.7761074471516","Facebook","" "Welcome Family Holiday Park","Dawlish Warren, Dawlish, South Devon EX7 0PH, United Kingdom","camping","+44 345 165 6265","https://www.welcomefamily.co.uk/","","50.6001833","-3.4476097","Facebook","ChIJ73pY0UQKbUgRNpirpCc6-tQ" "Welcome Family Holiday Park","Dawlish Warren, Dawlish, South Devon EX7 0PH, United Kingdom","camping","+44 345 165 6265","https://www.welcomefamily.co.uk/","","50.6001833","-3.4476097","Facebook","ChIJ73pY0UQKbUgRNpirpCc6-tQ" "Love Hate ","9 Brendon Road Bristol England BS20 6DJ United Kingdom","home","","","","51.482314952313","-2.78711266877407","Https://goo.gl/photos/pMYTnCir#What#Https://assets.contentstack.io#Youporn#Likes#Meee#Porn hub#Yup#Restaurant#🤑🚘#07538 552769#36 Hours In...Bath#07 38 552769#Bus stop#Checkins#Friend#Freeman#Contacts#36 Hours In...Bath#C3#Facebook#Busstopd#Hotel#Dmap","" "Lower Down","Portishead, Bristol BS20 6EB, UK","bowling","","","","51.48093799999999","-2.784538","Dan","ChIJ_xac6AfycUgRKmgffCqQHME" "358999/07/718825/8","thanks","generic","07358552769","","","undefined","undefined","🤑🚘","" "See","12-23 Gaunts Cl, Portishead, Bristol BS20 8BL, UK","casino","07502220198",".com","Gay","51.4779400858475","-2.79685295939177","Paije",""

[am11]

There is also a C implementation of huffman from Brotli in CoreFX: huffman.c, huffman.h, and System.IO.Compression.Brotli is referenced by System.Net.Http; could these be consolidated?

[geoffkizer]

I doubt that makes sense. The HPACK Huffman encoding is a static encoding that's specific to HPACK.

[mafshin]

I really enjoyed the conversation and co-operation between you devs to optimize those little things. Just here to say Thanks. 😶 Thank you Open source. Thank you Microsoft

[danmoseley]

@mafshin any interest in ongoing involvement? We have plenty of new API, fixes, and perf work up for grabs. We would be glad to have you.

(Note for those marked both up-for-grabs and api-needs-work the task is to make an API proposal for review. If api-approved the task is to implement the API.)

[karelz]

Triage: The idea is described above: https://github.com/dotnet/corefx/issues/31751#issuecomment-419618551

[rokonec]

Hi @geoffkizer, I was hooked up by this and gave it a try. I have build decoding table and run benchmark for several lookup bits size tables. I have managed to bring tables (static, pregenerated in source code, one dimensional array of ushort) to bellow sizes:	bytes	lookup bits
1008	2
1472	3
1728	4
3904	5
5248	6
7936	7
7680	8

I have also tried to optimize current algorithm, as I quite like the elegance and simplicity of it.

I have created micro benchmark by BenchmarkDotNet with following results:

Method	Mean	Error	StdDev	Op/s	Ratio
Current	1,822.29 ns	13.807 ns	12.240 ns	548,760.2	1.00
CurrentOptimized	1,050.57 ns	5.903 ns	5.522 ns	951,867.1	0.58
LookupBits2	1,674.67 ns	13.353 ns	12.491 ns	597,132.4	0.92
LookupBits3	1,213.27 ns	19.844 ns	18.562 ns	824,219.2	0.66
LookupBits4	1,126.86 ns	15.168 ns	13.446 ns	887,419.7	0.62
LookupBits5	922.54 ns	8.767 ns	8.201 ns	1,083,960.3	0.51
LookupBits6	762.84 ns	7.241 ns	6.419 ns	1,310,899.4	0.42
LookupBits7	642.59 ns	6.567 ns	5.821 ns	1,556,201.7	0.35
LookupBits8	641.35 ns	4.952 ns	4.632 ns	1,559,205.3	0.35

It runs and decode following strings which I hoped might be close to common usage:

• www.example.com
• no-cache
• upgrade-insecure-requests
• mEO7bfwFStBMwJWfW4pmg2XL25AswjrVlfcfYbxkcS2ssduZmiKoipMH9XwoTGkb+Qnq9bcjwWbwDQzsea/vMQ==

Benchmark shows, that there is compromise between size of static decoded table and decoding speed.

It also shows that current optimized algorithm can compete with lookup tables.

I do not feel I have enough context to make decision of what way to proceed as I am not aware of how costly is to have additional 8KB static table.

From my point of view I would go with CurrentOptimized for followign reasons:

• code is more readable and maintainable, to me, than lookuptable algorithm which is about 80 lines of shifts and ifs :-)
• less memory spent on static decoding table
• less chance of bug in code - although all tests we currently have are passing on my implementation of lookuptable it is not guaranteed those UT cover all possible failure modes

Would you recommend to proceed with PR for CurrentOptimized? This commit has the draft version of proposed changes. Todo is benchmark and one time 'monte carlo' tests comparing existing and new implementation results.

@karelz Can you please assign me to this issue?

[geoffkizer]

It would be good to see perf results that are not in the ~1us range; this is very short and the results are not necessarily representative in general. I'd suggest adding more input to your test.

Assuming that the test is representative, we would want to have this perf test in the tree in order to measure future changes/improvements.

I can't comment on any of the "lookup bits" variations without seeing the code.

If you have an improvement on the existing approach, then we would certainly consider taking that. It would be good to understand which changes are responsible for the improvements, and to what extent.

[rokonec]

I was using BenchmarkDotNet for those benchmarks. This tool compute number of invocation of benchmark methods to reach sufficient precision. Default behavior, which I used, is described here: --iterationTime - desired time of execution of an iteration. Used by Pilot stage to estimate the number of invocations per iteration. 500ms by default. I tried to run body of benchmark method 1e6 times with statistically identical results.

I plan to create and sumbit PR for bechmark into https://github.com/dotnet/aspnetcore/blob/master/src/Servers/Kestrel/perf/Kestrel.Performance/HPackDecoderBenchmark.cs as this seems to already have another perf benchmark related to HPack.

Bellow are links on 'draft' commits where you can see implementation of different algorithms.

---

Current optimized https://github.com/rokonec/runtime/commit/2c350184c2ace484f2350a8428d3d64426d5a3b2

Main speed improvements lies by replacing lines https://github.com/rokonec/runtime/blob/50ac454d8d8a1915188b2a4bb3fff3b81bf6c0cf/src/libraries/Common/tests/System/Net/Http/HuffmanDecoder.cs#L52-L56 by simple load and shift. As oppose to shift and rotate 5 bytes for every huffman code I preload data into UInt64 variable and use simple shift to extract value based on count of bits left in that buffer.

// we need exactly 32 bits of code, if there is less than 32 bits left in source, we have to fill missing bits by zeroes from LSB up
uint data = (uint)(bitsInAcc > 32 ? acc >> (bitsInAcc - 32) : acc << (32 - bitsInAcc));

---

Decoding by lookup table https://github.com/rokonec/runtime/commit/52229bbc3f948b6ae384e313e77c2120ce67ec69

Static lookup table is omitted for clarity.

[scalablecory]

We are generally not shy about going the extra mile for perf. I don't think your LUT code is concerning.

I am personally fine with an 8K LUT, but we've recently put in a lot of work to reducing assembly size and I would understand pushback. @stephentoub any thoughts here?

If it is a problem, then can the LUT be generated quickly at runtime? If yes, then I say lets go with the LookupBits8 version.

It would be useful to know how frequently Huffman-coded headers are used and how much they impact perf of a request. @JamesNK do you have any data here for gRPC?

[JamesNK]

All the gRPC spec headers are small so I doubt anyone is huffman encoding them. And they're common between requests so gRPC headers will be compressed with HPack.

[rokonec]

LUT could be generated quickly at runtime with about O(n log n) where n = 257 and body just about 10 fast lines. It should be possible to do it with just one allocation - the destination LUT ushort[].

[scalablecory]

LUT could be generated quickly at runtime with about O(n log n) where n = 257 and body just about 10 fast lines. It should be possible to do it with just one allocation - the destination LUT ushort[].

Lets just do this then.