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postgresql/src/backend/utils/adt/array_typanalyze.c

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/*-------------------------------------------------------------------------
*
* array_typanalyze.c
* Functions for gathering statistics from array columns
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/utils/adt/array_typanalyze.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/detoast.h"
#include "commands/vacuum.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"
/*
* To avoid consuming too much memory, IO and CPU load during analysis, and/or
* too much space in the resulting pg_statistic rows, we ignore arrays that
* are wider than ARRAY_WIDTH_THRESHOLD (after detoasting!). Note that this
* number is considerably more than the similar WIDTH_THRESHOLD limit used
* in analyze.c's standard typanalyze code.
*/
#define ARRAY_WIDTH_THRESHOLD 0x10000
/* Extra data for compute_array_stats function */
typedef struct
{
/* Information about array element type */
Oid type_id; /* element type's OID */
Oid eq_opr; /* default equality operator's OID */
Oid coll_id; /* collation to use */
bool typbyval; /* physical properties of element type */
int16 typlen;
char typalign;
/*
* Lookup data for element type's comparison and hash functions (these are
* in the type's typcache entry, which we expect to remain valid over the
* lifespan of the ANALYZE run)
*/
FmgrInfo *cmp;
FmgrInfo *hash;
/* Saved state from std_typanalyze() */
AnalyzeAttrComputeStatsFunc std_compute_stats;
void *std_extra_data;
} ArrayAnalyzeExtraData;
/*
* While compute_array_stats is running, we keep a pointer to the extra data
* here for use by assorted subroutines. compute_array_stats doesn't
* currently need to be re-entrant, so avoiding this is not worth the extra
* notational cruft that would be needed.
*/
static ArrayAnalyzeExtraData *array_extra_data;
/* A hash table entry for the Lossy Counting algorithm */
typedef struct
{
Datum key; /* This is 'e' from the LC algorithm. */
int frequency; /* This is 'f'. */
int delta; /* And this is 'delta'. */
int last_container; /* For de-duplication of array elements. */
} TrackItem;
/* A hash table entry for distinct-elements counts */
typedef struct
{
int count; /* Count of distinct elements in an array */
int frequency; /* Number of arrays seen with this count */
} DECountItem;
static void compute_array_stats(VacAttrStats *stats,
AnalyzeAttrFetchFunc fetchfunc, int samplerows, double totalrows);
static void prune_element_hashtable(HTAB *elements_tab, int b_current);
static uint32 element_hash(const void *key, Size keysize);
static int element_match(const void *key1, const void *key2, Size keysize);
static int element_compare(const void *key1, const void *key2);
static int trackitem_compare_frequencies_desc(const void *e1, const void *e2, void *arg);
static int trackitem_compare_element(const void *e1, const void *e2, void *arg);
static int countitem_compare_count(const void *e1, const void *e2, void *arg);
/*
* array_typanalyze -- typanalyze function for array columns
*/
Datum
array_typanalyze(PG_FUNCTION_ARGS)
{
VacAttrStats *stats = (VacAttrStats *) PG_GETARG_POINTER(0);
Oid element_typeid;
TypeCacheEntry *typentry;
ArrayAnalyzeExtraData *extra_data;
/*
* Call the standard typanalyze function. It may fail to find needed
* operators, in which case we also can't do anything, so just fail.
*/
if (!std_typanalyze(stats))
PG_RETURN_BOOL(false);
/*
* Check attribute data type is a varlena array (or a domain over one).
*/
element_typeid = get_base_element_type(stats->attrtypid);
if (!OidIsValid(element_typeid))
elog(ERROR, "array_typanalyze was invoked for non-array type %u",
stats->attrtypid);
/*
* Gather information about the element type. If we fail to find
* something, return leaving the state from std_typanalyze() in place.
*/
typentry = lookup_type_cache(element_typeid,
TYPECACHE_EQ_OPR |
TYPECACHE_CMP_PROC_FINFO |
TYPECACHE_HASH_PROC_FINFO);
if (!OidIsValid(typentry->eq_opr) ||
!OidIsValid(typentry->cmp_proc_finfo.fn_oid) ||
!OidIsValid(typentry->hash_proc_finfo.fn_oid))
PG_RETURN_BOOL(true);
/* Store our findings for use by compute_array_stats() */
extra_data = (ArrayAnalyzeExtraData *) palloc(sizeof(ArrayAnalyzeExtraData));
extra_data->type_id = typentry->type_id;
extra_data->eq_opr = typentry->eq_opr;
extra_data->coll_id = stats->attrcollid; /* collation we should use */
extra_data->typbyval = typentry->typbyval;
extra_data->typlen = typentry->typlen;
extra_data->typalign = typentry->typalign;
extra_data->cmp = &typentry->cmp_proc_finfo;
extra_data->hash = &typentry->hash_proc_finfo;
/* Save old compute_stats and extra_data for scalar statistics ... */
extra_data->std_compute_stats = stats->compute_stats;
extra_data->std_extra_data = stats->extra_data;
/* ... and replace with our info */
stats->compute_stats = compute_array_stats;
stats->extra_data = extra_data;
/*
* Note we leave stats->minrows set as std_typanalyze set it. Should it
* be increased for array analysis purposes?
*/
PG_RETURN_BOOL(true);
}
/*
* compute_array_stats() -- compute statistics for an array column
*
* This function computes statistics useful for determining selectivity of
* the array operators <@, &&, and @>. It is invoked by ANALYZE via the
* compute_stats hook after sample rows have been collected.
*
* We also invoke the standard compute_stats function, which will compute
* "scalar" statistics relevant to the btree-style array comparison operators.
* However, exact duplicates of an entire array may be rare despite many
* arrays sharing individual elements. This especially afflicts long arrays,
* which are also liable to lack all scalar statistics due to the low
* WIDTH_THRESHOLD used in analyze.c. So, in addition to the standard stats,
* we find the most common array elements and compute a histogram of distinct
* element counts.
*
* The algorithm used is Lossy Counting, as proposed in the paper "Approximate
* frequency counts over data streams" by G. S. Manku and R. Motwani, in
* Proceedings of the 28th International Conference on Very Large Data Bases,
* Hong Kong, China, August 2002, section 4.2. The paper is available at
* http://www.vldb.org/conf/2002/S10P03.pdf
*
* The Lossy Counting (aka LC) algorithm goes like this:
* Let s be the threshold frequency for an item (the minimum frequency we
* are interested in) and epsilon the error margin for the frequency. Let D
* be a set of triples (e, f, delta), where e is an element value, f is that
* element's frequency (actually, its current occurrence count) and delta is
* the maximum error in f. We start with D empty and process the elements in
* batches of size w. (The batch size is also known as "bucket size" and is
* equal to 1/epsilon.) Let the current batch number be b_current, starting
* with 1. For each element e we either increment its f count, if it's
* already in D, or insert a new triple into D with values (e, 1, b_current
* - 1). After processing each batch we prune D, by removing from it all
* elements with f + delta <= b_current. After the algorithm finishes we
* suppress all elements from D that do not satisfy f >= (s - epsilon) * N,
* where N is the total number of elements in the input. We emit the
* remaining elements with estimated frequency f/N. The LC paper proves
* that this algorithm finds all elements with true frequency at least s,
* and that no frequency is overestimated or is underestimated by more than
* epsilon. Furthermore, given reasonable assumptions about the input
* distribution, the required table size is no more than about 7 times w.
*
* In the absence of a principled basis for other particular values, we
* follow ts_typanalyze() and use parameters s = 0.07/K, epsilon = s/10.
* But we leave out the correction for stopwords, which do not apply to
* arrays. These parameters give bucket width w = K/0.007 and maximum
* expected hashtable size of about 1000 * K.
*
* Elements may repeat within an array. Since duplicates do not change the
* behavior of <@, && or @>, we want to count each element only once per
* array. Therefore, we store in the finished pg_statistic entry each
* element's frequency as the fraction of all non-null rows that contain it.
* We divide the raw counts by nonnull_cnt to get those figures.
*/
static void
compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
int samplerows, double totalrows)
{
ArrayAnalyzeExtraData *extra_data;
int num_mcelem;
int null_elem_cnt = 0;
int analyzed_rows = 0;
/* This is D from the LC algorithm. */
HTAB *elements_tab;
HASHCTL elem_hash_ctl;
HASH_SEQ_STATUS scan_status;
/* This is the current bucket number from the LC algorithm */
int b_current;
/* This is 'w' from the LC algorithm */
int bucket_width;
int array_no;
int64 element_no;
TrackItem *item;
int slot_idx;
HTAB *count_tab;
HASHCTL count_hash_ctl;
DECountItem *count_item;
extra_data = (ArrayAnalyzeExtraData *) stats->extra_data;
/*
* Invoke analyze.c's standard analysis function to create scalar-style
* stats for the column. It will expect its own extra_data pointer, so
* temporarily install that.
*/
stats->extra_data = extra_data->std_extra_data;
extra_data->std_compute_stats(stats, fetchfunc, samplerows, totalrows);
stats->extra_data = extra_data;
/*
* Set up static pointer for use by subroutines. We wait till here in
* case std_compute_stats somehow recursively invokes us (probably not
* possible, but ...)
*/
array_extra_data = extra_data;
/*
* We want statistics_target * 10 elements in the MCELEM array. This
* multiplier is pretty arbitrary, but is meant to reflect the fact that
* the number of individual elements tracked in pg_statistic ought to be
* more than the number of values for a simple scalar column.
*/
num_mcelem = stats->attr->attstattarget * 10;
/*
* We set bucket width equal to num_mcelem / 0.007 as per the comment
* above.
*/
bucket_width = num_mcelem * 1000 / 7;
/*
* Create the hashtable. It will be in local memory, so we don't need to
* worry about overflowing the initial size. Also we don't need to pay any
* attention to locking and memory management.
*/
elem_hash_ctl.keysize = sizeof(Datum);
elem_hash_ctl.entrysize = sizeof(TrackItem);
elem_hash_ctl.hash = element_hash;
elem_hash_ctl.match = element_match;
elem_hash_ctl.hcxt = CurrentMemoryContext;
elements_tab = hash_create("Analyzed elements table",
num_mcelem,
&elem_hash_ctl,
HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
/* hashtable for array distinct elements counts */
count_hash_ctl.keysize = sizeof(int);
count_hash_ctl.entrysize = sizeof(DECountItem);
count_hash_ctl.hcxt = CurrentMemoryContext;
count_tab = hash_create("Array distinct element count table",
64,
&count_hash_ctl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
/* Initialize counters. */
b_current = 1;
element_no = 0;
/* Loop over the arrays. */
for (array_no = 0; array_no < samplerows; array_no++)
{
Datum value;
bool isnull;
ArrayType *array;
int num_elems;
Datum *elem_values;
bool *elem_nulls;
bool null_present;
int j;
int64 prev_element_no = element_no;
int distinct_count;
bool count_item_found;
vacuum_delay_point();
value = fetchfunc(stats, array_no, &isnull);
if (isnull)
{
/* ignore arrays that are null overall */
continue;
}
/* Skip too-large values. */
if (toast_raw_datum_size(value) > ARRAY_WIDTH_THRESHOLD)
continue;
else
analyzed_rows++;
/*
* Now detoast the array if needed, and deconstruct into datums.
*/
array = DatumGetArrayTypeP(value);
Assert(ARR_ELEMTYPE(array) == extra_data->type_id);
deconstruct_array(array,
extra_data->type_id,
extra_data->typlen,
extra_data->typbyval,
extra_data->typalign,
&elem_values, &elem_nulls, &num_elems);
/*
* We loop through the elements in the array and add them to our
* tracking hashtable.
*/
null_present = false;
for (j = 0; j < num_elems; j++)
{
Datum elem_value;
bool found;
/* No null element processing other than flag setting here */
if (elem_nulls[j])
{
null_present = true;
continue;
}
/* Lookup current element in hashtable, adding it if new */
elem_value = elem_values[j];
item = (TrackItem *) hash_search(elements_tab,
(const void *) &elem_value,
HASH_ENTER, &found);
if (found)
{
/* The element value is already on the tracking list */
/*
* The operators we assist ignore duplicate array elements, so
* count a given distinct element only once per array.
*/
if (item->last_container == array_no)
continue;
item->frequency++;
item->last_container = array_no;
}
else
{
/* Initialize new tracking list element */
/*
* If element type is pass-by-reference, we must copy it into
* palloc'd space, so that we can release the array below. (We
* do this so that the space needed for element values is
* limited by the size of the hashtable; if we kept all the
* array values around, it could be much more.)
*/
item->key = datumCopy(elem_value,
extra_data->typbyval,
extra_data->typlen);
item->frequency = 1;
item->delta = b_current - 1;
item->last_container = array_no;
}
/* element_no is the number of elements processed (ie N) */
element_no++;
/* We prune the D structure after processing each bucket */
if (element_no % bucket_width == 0)
{
prune_element_hashtable(elements_tab, b_current);
b_current++;
}
}
/* Count null element presence once per array. */
if (null_present)
null_elem_cnt++;
/* Update frequency of the particular array distinct element count. */
distinct_count = (int) (element_no - prev_element_no);
count_item = (DECountItem *) hash_search(count_tab, &distinct_count,
HASH_ENTER,
&count_item_found);
if (count_item_found)
count_item->frequency++;
else
count_item->frequency = 1;
/* Free memory allocated while detoasting. */
if (PointerGetDatum(array) != value)
pfree(array);
pfree(elem_values);
pfree(elem_nulls);
}
/* Skip pg_statistic slots occupied by standard statistics */
slot_idx = 0;
while (slot_idx < STATISTIC_NUM_SLOTS && stats->stakind[slot_idx] != 0)
slot_idx++;
if (slot_idx > STATISTIC_NUM_SLOTS - 2)
elog(ERROR, "insufficient pg_statistic slots for array stats");
/* We can only compute real stats if we found some non-null values. */
if (analyzed_rows > 0)
{
int nonnull_cnt = analyzed_rows;
int count_items_count;
int i;
TrackItem **sort_table;
int track_len;
int64 cutoff_freq;
int64 minfreq,
maxfreq;
/*
* We assume the standard stats code already took care of setting
* stats_valid, stanullfrac, stawidth, stadistinct. We'd have to
* re-compute those values if we wanted to not store the standard
* stats.
*/
/*
* Construct an array of the interesting hashtable items, that is,
* those meeting the cutoff frequency (s - epsilon)*N. Also identify
* the minimum and maximum frequencies among these items.
*
* Since epsilon = s/10 and bucket_width = 1/epsilon, the cutoff
* frequency is 9*N / bucket_width.
*/
cutoff_freq = 9 * element_no / bucket_width;
i = hash_get_num_entries(elements_tab); /* surely enough space */
sort_table = (TrackItem **) palloc(sizeof(TrackItem *) * i);
hash_seq_init(&scan_status, elements_tab);
track_len = 0;
minfreq = element_no;
maxfreq = 0;
while ((item = (TrackItem *) hash_seq_search(&scan_status)) != NULL)
{
if (item->frequency > cutoff_freq)
{
sort_table[track_len++] = item;
minfreq = Min(minfreq, item->frequency);
maxfreq = Max(maxfreq, item->frequency);
}
}
Assert(track_len <= i);
/* emit some statistics for debug purposes */
elog(DEBUG3, "compute_array_stats: target # mces = %d, "
"bucket width = %d, "
"# elements = " INT64_FORMAT ", hashtable size = %d, "
"usable entries = %d",
num_mcelem, bucket_width, element_no, i, track_len);
/*
* If we obtained more elements than we really want, get rid of those
* with least frequencies. The easiest way is to qsort the array into
* descending frequency order and truncate the array.
*/
if (num_mcelem < track_len)
{
qsort_interruptible(sort_table, track_len, sizeof(TrackItem *),
trackitem_compare_frequencies_desc, NULL);
/* reset minfreq to the smallest frequency we're keeping */
minfreq = sort_table[num_mcelem - 1]->frequency;
}
else
num_mcelem = track_len;
/* Generate MCELEM slot entry */
if (num_mcelem > 0)
{
MemoryContext old_context;
Datum *mcelem_values;
float4 *mcelem_freqs;
/*
* We want to store statistics sorted on the element value using
* the element type's default comparison function. This permits
* fast binary searches in selectivity estimation functions.
*/
qsort_interruptible(sort_table, num_mcelem, sizeof(TrackItem *),
trackitem_compare_element, NULL);
/* Must copy the target values into anl_context */
old_context = MemoryContextSwitchTo(stats->anl_context);
/*
* We sorted statistics on the element value, but we want to be
* able to find the minimal and maximal frequencies without going
* through all the values. We also want the frequency of null
* elements. Store these three values at the end of mcelem_freqs.
*/
mcelem_values = (Datum *) palloc(num_mcelem * sizeof(Datum));
mcelem_freqs = (float4 *) palloc((num_mcelem + 3) * sizeof(float4));
/*
* See comments above about use of nonnull_cnt as the divisor for
* the final frequency estimates.
*/
for (i = 0; i < num_mcelem; i++)
{
TrackItem *item = sort_table[i];
mcelem_values[i] = datumCopy(item->key,
extra_data->typbyval,
extra_data->typlen);
mcelem_freqs[i] = (double) item->frequency /
(double) nonnull_cnt;
}
mcelem_freqs[i++] = (double) minfreq / (double) nonnull_cnt;
mcelem_freqs[i++] = (double) maxfreq / (double) nonnull_cnt;
mcelem_freqs[i++] = (double) null_elem_cnt / (double) nonnull_cnt;
MemoryContextSwitchTo(old_context);
stats->stakind[slot_idx] = STATISTIC_KIND_MCELEM;
stats->staop[slot_idx] = extra_data->eq_opr;
stats->stacoll[slot_idx] = extra_data->coll_id;
stats->stanumbers[slot_idx] = mcelem_freqs;
/* See above comment about extra stanumber entries */
stats->numnumbers[slot_idx] = num_mcelem + 3;
stats->stavalues[slot_idx] = mcelem_values;
stats->numvalues[slot_idx] = num_mcelem;
/* We are storing values of element type */
stats->statypid[slot_idx] = extra_data->type_id;
stats->statyplen[slot_idx] = extra_data->typlen;
stats->statypbyval[slot_idx] = extra_data->typbyval;
stats->statypalign[slot_idx] = extra_data->typalign;
slot_idx++;
}
/* Generate DECHIST slot entry */
count_items_count = hash_get_num_entries(count_tab);
if (count_items_count > 0)
{
int num_hist = stats->attr->attstattarget;
DECountItem **sorted_count_items;
int j;
int delta;
int64 frac;
float4 *hist;
/* num_hist must be at least 2 for the loop below to work */
num_hist = Max(num_hist, 2);
/*
* Create an array of DECountItem pointers, and sort them into
* increasing count order.
*/
sorted_count_items = (DECountItem **)
palloc(sizeof(DECountItem *) * count_items_count);
hash_seq_init(&scan_status, count_tab);
j = 0;
while ((count_item = (DECountItem *) hash_seq_search(&scan_status)) != NULL)
{
sorted_count_items[j++] = count_item;
}
qsort_interruptible(sorted_count_items, count_items_count,
sizeof(DECountItem *),
countitem_compare_count, NULL);
/*
* Prepare to fill stanumbers with the histogram, followed by the
* average count. This array must be stored in anl_context.
*/
hist = (float4 *)
MemoryContextAlloc(stats->anl_context,
sizeof(float4) * (num_hist + 1));
hist[num_hist] = (double) element_no / (double) nonnull_cnt;
/*----------
* Construct the histogram of distinct-element counts (DECs).
*
* The object of this loop is to copy the min and max DECs to
* hist[0] and hist[num_hist - 1], along with evenly-spaced DECs
* in between (where "evenly-spaced" is with reference to the
* whole input population of arrays). If we had a complete sorted
* array of DECs, one per analyzed row, the i'th hist value would
* come from DECs[i * (analyzed_rows - 1) / (num_hist - 1)]
* (compare the histogram-making loop in compute_scalar_stats()).
* But instead of that we have the sorted_count_items[] array,
* which holds unique DEC values with their frequencies (that is,
* a run-length-compressed version of the full array). So we
* control advancing through sorted_count_items[] with the
* variable "frac", which is defined as (x - y) * (num_hist - 1),
* where x is the index in the notional DECs array corresponding
* to the start of the next sorted_count_items[] element's run,
* and y is the index in DECs from which we should take the next
* histogram value. We have to advance whenever x <= y, that is
* frac <= 0. The x component is the sum of the frequencies seen
* so far (up through the current sorted_count_items[] element),
* and of course y * (num_hist - 1) = i * (analyzed_rows - 1),
* per the subscript calculation above. (The subscript calculation
* implies dropping any fractional part of y; in this formulation
* that's handled by not advancing until frac reaches 1.)
*
* Even though frac has a bounded range, it could overflow int32
* when working with very large statistics targets, so we do that
* math in int64.
*----------
*/
delta = analyzed_rows - 1;
j = 0; /* current index in sorted_count_items */
/* Initialize frac for sorted_count_items[0]; y is initially 0 */
frac = (int64) sorted_count_items[0]->frequency * (num_hist - 1);
for (i = 0; i < num_hist; i++)
{
while (frac <= 0)
{
/* Advance, and update x component of frac */
j++;
frac += (int64) sorted_count_items[j]->frequency * (num_hist - 1);
}
hist[i] = sorted_count_items[j]->count;
frac -= delta; /* update y for upcoming i increment */
}
Assert(j == count_items_count - 1);
stats->stakind[slot_idx] = STATISTIC_KIND_DECHIST;
stats->staop[slot_idx] = extra_data->eq_opr;
stats->stacoll[slot_idx] = extra_data->coll_id;
stats->stanumbers[slot_idx] = hist;
stats->numnumbers[slot_idx] = num_hist + 1;
slot_idx++;
}
}
/*
* We don't need to bother cleaning up any of our temporary palloc's. The
* hashtable should also go away, as it used a child memory context.
*/
}
/*
* A function to prune the D structure from the Lossy Counting algorithm.
* Consult compute_tsvector_stats() for wider explanation.
*/
static void
prune_element_hashtable(HTAB *elements_tab, int b_current)
{
HASH_SEQ_STATUS scan_status;
TrackItem *item;
hash_seq_init(&scan_status, elements_tab);
while ((item = (TrackItem *) hash_seq_search(&scan_status)) != NULL)
{
if (item->frequency + item->delta <= b_current)
{
Datum value = item->key;
if (hash_search(elements_tab, (const void *) &item->key,
HASH_REMOVE, NULL) == NULL)
elog(ERROR, "hash table corrupted");
/* We should free memory if element is not passed by value */
if (!array_extra_data->typbyval)
pfree(DatumGetPointer(value));
}
}
}
/*
* Hash function for elements.
*
* We use the element type's default hash opclass, and the column collation
* if the type is collation-sensitive.
*/
static uint32
element_hash(const void *key, Size keysize)
{
Datum d = *((const Datum *) key);
Datum h;
h = FunctionCall1Coll(array_extra_data->hash,
array_extra_data->coll_id,
d);
return DatumGetUInt32(h);
}
/*
* Matching function for elements, to be used in hashtable lookups.
*/
static int
element_match(const void *key1, const void *key2, Size keysize)
{
/* The keysize parameter is superfluous here */
return element_compare(key1, key2);
}
/*
* Comparison function for elements.
*
* We use the element type's default btree opclass, and the column collation
* if the type is collation-sensitive.
*
* XXX consider using SortSupport infrastructure
*/
static int
element_compare(const void *key1, const void *key2)
{
Datum d1 = *((const Datum *) key1);
Datum d2 = *((const Datum *) key2);
Datum c;
c = FunctionCall2Coll(array_extra_data->cmp,
array_extra_data->coll_id,
d1, d2);
return DatumGetInt32(c);
}
/*
* Comparator for sorting TrackItems by frequencies (descending sort)
*/
static int
trackitem_compare_frequencies_desc(const void *e1, const void *e2, void *arg)
{
const TrackItem *const *t1 = (const TrackItem *const *) e1;
const TrackItem *const *t2 = (const TrackItem *const *) e2;
return (*t2)->frequency - (*t1)->frequency;
}
/*
* Comparator for sorting TrackItems by element values
*/
static int
trackitem_compare_element(const void *e1, const void *e2, void *arg)
{
const TrackItem *const *t1 = (const TrackItem *const *) e1;
const TrackItem *const *t2 = (const TrackItem *const *) e2;
return element_compare(&(*t1)->key, &(*t2)->key);
}
/*
* Comparator for sorting DECountItems by count
*/
static int
countitem_compare_count(const void *e1, const void *e2, void *arg)
{
const DECountItem *const *t1 = (const DECountItem *const *) e1;
const DECountItem *const *t2 = (const DECountItem *const *) e2;
if ((*t1)->count < (*t2)->count)
return -1;
else if ((*t1)->count == (*t2)->count)
return 0;
else
return 1;
}
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