# HG changeset patch
# User Boris Feld <boris.f...@octobus.net>
# Date 1541785632 -3600
# Fri Nov 09 18:47:12 2018 +0100
# Node ID 4a1104eade1dfb1697517d60d2c5fd7a98b8c7f0
# Parent 0ea42453fa491793d1e145f5093b65e84cb65e97
# EXP-Topic sparse-perf
# Available At https://bitbucket.org/octobus/mercurial-devel/
# hg pull https://bitbucket.org/octobus/mercurial-devel/ -r
4a1104eade1d
sparse-revlog: introduce native (C) implementation of slicechunktodensity
This is a C implementation of `_slicechunktodensity` in the
`mercurial/revlogutils/deltas.py` file.
The algorithm involves a lot of integer manipulation and low-level access to
index data. Having a C implementation of it raises a large performance
improvement. See later changeset in this series for details.
diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -11,6 +11,7 @@
#include <assert.h>
#include <ctype.h>
#include <stddef.h>
+#include <stdlib.h>
#include <string.h>
#include "bitmanipulation.h"
@@ -1041,6 +1042,197 @@ static PyObject *_trimchunk(indexObject
return chunk;
}
+struct Gap {
+ long size;
+ long idx;
+};
+
+static int gap_compare(const void *left, const void *right)
+{
+ return ((struct Gap *)left)->size - ((struct Gap *)right)->size;
+}
+static int long_compare(const void *left, const void *right)
+{
+ return *(long *)left - *(long *)right;
+}
+
+static PyObject *index_slicechunktodensity(indexObject *self, PyObject *args)
+{
+ /* method arguments */
+ PyObject *list_revs = NULL; /* revisions in the chain */
+ double targetdensity = 0.5; /* min density to achieve */
+ long mingapsize = 0; /* threshold to ignore gaps */
+
+ /* other core variables */
+ long i; /* used for various iteration */
+ PyObject *result = NULL; /* the final return of the function */
+
+ /* generic information about the delta chain being slice */
+ Py_ssize_t num_revs = 0; /* size of the full delta chain */
+ Py_ssize_t *revs = NULL; /* native array of revision in the chain */
+ long chainpayload = 0; /* sum of all delta in the chain */
+ long deltachainspan = 0; /* distance from first byte to last byte */
+
+ /* variable used for slicing the delta chain */
+ long readdata = 0; /* amount of data currently planned to be read */
+ double density = 0; /* ration of payload data compared to read ones */
+ struct Gap *gaps = NULL; /* array of notable gap in the chain */
+ long num_gaps = 0; /* total number of notable gap recorded so far */
+ Py_ssize_t *selected_indices = NULL; /* indices of gap skipped over */
+ long num_selected = 0; /* number of gaps skipped */
+ PyObject *chunk = NULL; /* individual slice */
+ PyObject *allchunks = PyList_New(num_selected); /* all slices */
+
+ /* parsing argument */
+ if (!PyArg_ParseTuple(args, "O!dl", &PyList_Type, &list_revs,
+ &targetdensity, &mingapsize)) {
+ goto bail;
+ }
+
+ /* If the delta chain contains a single element, we do not need slicing
+ */
+ num_revs = PyList_GET_SIZE(list_revs);
+ if (num_revs <= 1) {
+ result = PyTuple_Pack(1, list_revs);
+ goto done;
+ }
+
+ /* Turn the python list into a native integer array (for efficiency) */
+ revs = (Py_ssize_t *)malloc((num_revs) * sizeof(Py_ssize_t));
+ if (revs == NULL) {
+ PyErr_NoMemory();
+ goto bail;
+ }
+ for (i = 0; i < num_revs; i++) {
+ Py_ssize_t revnum = PyInt_AsLong(PyList_GET_ITEM(list_revs, i));
+ if (revnum == -1 && PyErr_Occurred()) {
+ goto bail;
+ }
+ revs[i] = revnum;
+ }
+
+ /* Compute and check various property of the unsliced delta chain */
+ deltachainspan = index_segment_span(self, revs[0], revs[num_revs - 1]);
+
+ if (deltachainspan <= mingapsize) {
+ result = PyTuple_Pack(1, list_revs);
+ goto done;
+ }
+ chainpayload = 0;
+ for (i = 0; i < num_revs; i++) {
+ chainpayload += index_get_length(self, revs[i]);
+ }
+
+ readdata = deltachainspan;
+ density = 1.0;
+
+ if (0 < deltachainspan) {
+ density = (double)chainpayload / (double)deltachainspan;
+ };
+
+ if (density >= targetdensity) {
+ result = PyTuple_Pack(1, list_revs);
+ goto done;
+ }
+
+ /* if chain is too sparse, look for relevant gaps */
+ gaps = (struct Gap *)malloc((num_revs) * sizeof(struct Gap));
+ if (gaps == NULL) {
+ PyErr_NoMemory();
+ goto bail;
+ }
+
+ Py_ssize_t previous_end = -1;
+ for (i = 0; i < num_revs; i++) {
+ Py_ssize_t revstart = index_get_start(self, revs[i]);
+ Py_ssize_t revsize = index_get_length(self, revs[i]);
+ if (revsize <= 0) {
+ continue;
+ }
+ if (previous_end >= 0) {
+ Py_ssize_t gapsize = revstart - previous_end;
+ if (gapsize > mingapsize) {
+ gaps[num_gaps].size = gapsize;
+ gaps[num_gaps].idx = i;
+ num_gaps += 1;
+ }
+ }
+ previous_end = revstart + revsize;
+ }
+ if (num_gaps == 0) {
+ result = PyTuple_Pack(1, list_revs);
+ goto done;
+ }
+ qsort(gaps, num_gaps, sizeof(struct Gap), &gap_compare);
+
+ /* Slice the largest gap first, they improve the density the most */
+ selected_indices =
+ (Py_ssize_t *)malloc((num_gaps + 1) * sizeof(Py_ssize_t));
+ if (selected_indices == NULL) {
+ PyErr_NoMemory();
+ goto bail;
+ }
+
+ for (i = num_gaps - 1; i >= 0; i--) {
+ selected_indices[num_selected] = gaps[i].idx;
+ readdata -= gaps[i].size;
+ num_selected += 1;
+ if (readdata <= 0) {
+ density = 1.0;
+ } else {
+ density = (double)chainpayload / (double)readdata;
+ }
+ if (density >= targetdensity) {
+ break;
+ }
+ }
+ qsort(selected_indices, num_selected, sizeof(Py_ssize_t),
+ &long_compare);
+
+ /* create the resulting slice */
+ long previdx = 0;
+ selected_indices[num_selected] = num_revs;
+ for (i = 0; i <= num_selected; i++) {
+ long idx = selected_indices[i];
+ chunk = _trimchunk(self, list_revs, previdx, idx);
+ if (chunk == NULL) {
+ goto bail;
+ }
+ if (PyList_GET_SIZE(chunk) > 0) {
+ if (PyList_Append(allchunks, chunk) == -1) {
+ goto bail;
+ }
+ }
+ Py_DECREF(chunk);
+ chunk = NULL;
+ previdx = idx;
+ }
+ result = allchunks;
+ goto done;
+
+bail:
+ if (allchunks != NULL) {
+ Py_DECREF(allchunks);
+ }
+ if (chunk != NULL) {
+ Py_DECREF(chunk);
+ }
+done:
+ if (revs != NULL) {
+ free(revs);
+ }
+ if (gaps != NULL) {
+ free(gaps);
+ }
+ if (selected_indices != NULL) {
+ free(selected_indices);
+ }
+ if (result != NULL) {
+ Py_INCREF(result);
+ }
+ return result;
+}
+
static inline int nt_level(const char *node, Py_ssize_t level)
{
int v = node[level >> 1];
@@ -2265,6 +2457,8 @@ static PyMethodDef index_methods[] = {
"get filtered head revisions"}, /* Can always do filtering */
{"deltachain", (PyCFunction)index_deltachain, METH_VARARGS,
"determine revisions with deltas to reconstruct fulltext"},
+ {"slicechunktodensity", (PyCFunction)index_slicechunktodensity,
+ METH_VARARGS, "determine revisions with deltas to reconstruct fulltext"},
{"append", (PyCFunction)index_append, METH_O, "append an index entry"},
{"partialmatch", (PyCFunction)index_partialmatch, METH_VARARGS,
"match a potentially ambiguous node ID"},
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