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chore: improve debug compression #4735

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Mar 9, 2025
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chore: improve debug compression #4735

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63 changes: 25 additions & 38 deletions src/server/debugcmd.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -318,35 +318,13 @@ void DoBuildObjHist(EngineShard* shard, ConnectionContext* cntx, ObjHistMap* obj
}
}

void FillDictSamples(PrimeTable* table, string* sample_buf) {
PrimeTable::Cursor cursor;
unsigned steps = 0;
string scratch;
constexpr size_t kMaxLen = 512;
do {
cursor = table->Traverse(cursor, [&](PrimeIterator it) {
it->first.GetString(&scratch);
size_t len = std::min(scratch.size(), kMaxLen);
sample_buf->append(scratch.data(), len);
});

if (sample_buf->size() > 1_MB)
return;

if (steps >= 20000) {
steps = 0;
ThisFiber::Yield();
}
} while (cursor);
}

struct HufHist {
static constexpr unsigned kMaxSymbol = 255;
unsigned hist[kMaxSymbol + 1]; // histogram of symbols.
unsigned max_symbol = 0; // what is the max symbol of the histogram.
array<unsigned, kMaxSymbol + 1> hist; // histogram of symbols.
unsigned max_symbol = 0; // what is the max symbol of the histogram.

HufHist() {
memset(hist, 0, sizeof(hist));
hist.fill(0);
}

void Merge(const HufHist& other) {
Expand All @@ -362,18 +340,27 @@ void DoComputeHist(EngineShard* shard, ConnectionContext* cntx, HufHist* dest) {
DbTable* dbt = db_slice.GetDBTable(cntx->db_index());
CHECK(dbt);

string sample_buf;
FillDictSamples(&dbt->prime, &sample_buf);
PrimeTable::Cursor cursor;
unsigned steps = 0;
string scratch;
constexpr size_t kMaxLen = 512;
PrimeTable& table = dbt->prime;

if (sample_buf.empty()) {
return;
}
dest->max_symbol = 255;
do {
cursor = table.Traverse(cursor, [&](PrimeIterator it) {
it->first.GetString(&scratch);
size_t len = std::min(scratch.size(), kMaxLen);
HIST_add(dest->hist.data(), scratch.data(), len);
});

unique_ptr<uint32_t[]> wksp(new uint32_t[HIST_WKSP_SIZE_U32]);
size_t max_freq = HIST_count_wksp(dest->hist, &dest->max_symbol, sample_buf.data(),
sample_buf.size(), wksp.get(), HIST_WKSP_SIZE);
CHECK(!HIST_isError(max_freq));
if (steps >= 20000) {
steps = 0;
ThisFiber::Yield();
}
} while (cursor);
dest->max_symbol = HufHist::kMaxSymbol;
while (dest->max_symbol && dest->hist[dest->max_symbol] == 0)
--dest->max_symbol;
}

ObjInfo InspectOp(ConnectionContext* cntx, string_view key) {
Expand Down Expand Up @@ -1300,10 +1287,10 @@ void DebugCmd::Compression(facade::SinkReplyBuilder* builder) {
if (hist.max_symbol) {
unique_ptr<uint32_t[]> wrkspace(new uint32_t[HUF_CTABLE_WORKSPACE_SIZE_U32]);
constexpr size_t kWspSize = HUF_CTABLE_WORKSPACE_SIZE;
num_bits =
HUF_buildCTable_wksp(huf_ctable, hist.hist, hist.max_symbol, 0, wrkspace.get(), kWspSize);
num_bits = HUF_buildCTable_wksp(huf_ctable, hist.hist.data(), hist.max_symbol, 0,
wrkspace.get(), kWspSize);

compressed_size = HUF_estimateCompressedSize(huf_ctable, hist.hist, hist.max_symbol);
compressed_size = HUF_estimateCompressedSize(huf_ctable, hist.hist.data(), hist.max_symbol);
raw_size = 0;
for (unsigned i = 0; i < hist.max_symbol; i++) {
raw_size += hist.hist[i];
Expand Down
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