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Speed up SQL aggregate functions percentile() and median() by avoiding a full sort of the array of arguments.

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FossilOrigin-Name: 9232b5f21d76dc702ccda5c689d61bcd0057fb1f2a4db6a70c607c25ad03a027
This commit is contained in:
dan
2026-06-13 20:16:54 +00:00
parent 2884421c05
commit 36e9e015de
4 changed files with 57 additions and 27 deletions
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manifest
+9 -7
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@@ -1,5 +1,5 @@
C When\sreading\sa\ssuper-journal\sname\sfrom\sa\sjournal\sfile,\sallocate\sa\snew\sbuffer\srather\sthan\susing\sPager.pTmpSpace.\sThis\sprevents\sa\sbuffer\soverrun\sthat\scould\soccur\swhen\susing\sa\sVFS\swith\sa\slarge\ssqlite3_vfs.mxPathname\svalue\swith\sa\sdatabase\swith\sa\ssmall\spage\ssize.
D 2026-06-12T18:35:24.464
C Speed\sup\sSQL\saggregate\sfunctions\spercentile()\sand\smedian()\sby\savoiding\sa\sfull\ssort\sof\sthe\sarray\sof\sarguments.
D 2026-06-13T20:16:54.656
F .fossil-settings/binary-glob 61195414528fb3ea9693577e1980230d78a1f8b0a54c78cf1b9b24d0a409ed6a x
F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
@@ -692,7 +692,7 @@ F src/delete.c 59eeca3fb88c29329afc41bb803ee568b120d9dd7470b5f38ab55cc38390b451
F src/expr.c e97dd9f6ada4c448764e225d8963091bf630b3efb2c92e4d0762571cca2a14e5
F src/fault.c 460f3e55994363812d9d60844b2a6de88826e007
F src/fkey.c 931f74cec1dc8038a0217ef340c91ce147dd1bbed08dc40c47ee0ec6edfffb08
F src/func.c 555d5f7686f9eef20fe3574889403f307a6cb16ada5b05cbc6a9288dcf75aaeb
F src/func.c 038e454176de1729cc2a1fccce5629d86cc3fa6860546ba54827b394b1a5b4ed
F src/global.c a19e4b1ca1335f560e9560e590fc13081e21f670643367f99cb9e8f9dc7d615b
F src/hash.c 03c8c0f4be9e8bcb6de65aa26d34a61d48a9430747084a69f9469fbb00ea52ca
F src/hash.h 46b92795a95bfefb210f52f0c316e9d7cdbcdd7e7fcfb0d8be796d3a5767cddf
@@ -2209,9 +2209,11 @@ F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee
F tool/warnings.sh a554d13f6e5cf3760f041b87939e3d616ec6961859c3245e8ef701d1eafc2ca2
F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
F tool/winmain.c 00c8fb88e365c9017db14c73d3c78af62194d9644feaf60e220ab0f411f3604c
P f15d076820f4a0d9e7fa32d99575bce27bde5e987bb415e6cfb69b06f0da7e1e ac17669e840dbac5c7c75e9b6014cca2d289aba8de36f9d1d0d61186e8cc6207
R b4784016cdc66719536104e64f4ddb51
T +closed ac17669e840dbac5c7c75e9b6014cca2d289aba8de36f9d1d0d61186e8cc6207
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R 440eb116549bb7b7e06b073447b72a9b
T *branch * pecentile-partial-sort
T *sym-pecentile-partial-sort *
T -sym-trunk *
U dan
Z ae30c5c61ab231f09fb1164a547a0499
Z 2032cb49443943956dfcd7d4c638a43c
# Remove this line to create a well-formed Fossil manifest.
manifest.tags
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branch trunk
tag trunk
branch pecentile-partial-sort
tag pecentile-partial-sort
manifest.uuid
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@@ -1 +1 @@
7f71859841af7cb0806f58e9c8013a990fcca72b807a0513156d7127ce5c7b62
9232b5f21d76dc702ccda5c689d61bcd0057fb1f2a4db6a70c607c25ad03a027
src/func.c
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@@ -2967,8 +2967,17 @@ static void percentStep(sqlite3_context *pCtx, int argc, sqlite3_value **argv){
** (1) To avoid a dependency on qsort()
** (2) To avoid the function call to the comparison routine for each
** comparison.
**
** If parameter iReq is non-negative, then the caller will only access
** elements a[iReq] and a[iReq+1] (if it exists) of the sorted array and
** so it is not necessary to position any other elements. Or if iReq is
** negative, then the final array must be fully sorted.
*/
static void percentSort(double *a, unsigned int n){
static void percentSort(
double *a, /* Array to sort */
unsigned int n, /* Number of elements in array a[] */
int iReq /* Element caller cares about (or -ve) */
){
int iLt; /* Entries before a[iLt] are less than rPivot */
int iGt; /* Entries at or after a[iGt] are greater than rPivot */
int i; /* Loop counter */
@@ -3005,17 +3014,36 @@ static void percentSort(double *a, unsigned int n){
}
}while( i<iGt );
/* Recurse on the smaller partition only. The smaller partition
** will hold n/2 or fewer entries, which assures that the stack
** depth will not exceed O(log(n)), even for pathological cases.
** Loop without recursion for the larger partition. */
if( iLt>(int)(n/2) ){
if( n-iGt>=2 ) percentSort(a+iGt, n-iGt);
n = iLt;
assert( a[iLt]==rPivot );
assert( iGt>iLt );
if( iReq>=0 ){
/* In this case, the only elements that the caller requires sorted into
** the correct positions are elements a[iReq] and a[iReq+1]. At this
** point we know that element a[iLt] is in the correct position, so if
** iReq is less than iLt, it is only necessary to sort the first
** partition. Or, if iReq is greater than or equal to iLt, it is only
** necessary to sort the second. */
if( iReq<iLt ){
n = iLt;
}else{
a += iGt;
n -= iGt;
iReq = MAX(0, iReq-iGt);
}
}else{
if( iLt>=2 ) percentSort(a, iLt);
a += iGt;
n -= iGt;
/* Recurse on the smaller partition only. The smaller partition
** will hold n/2 or fewer entries, which assures that the stack
** depth will not exceed O(log(n)), even for pathological cases.
** Loop without recursion for the larger partition. */
if( iLt>(int)(n/2) ){
if( n-iGt>=2 ) percentSort(a+iGt, n-iGt, -1);
n = iLt;
}else{
if( iLt>=2 ) percentSort(a, iLt, -1);
a += iGt;
n -= iGt;
}
}
}while( n>=2 );
}
@@ -3052,7 +3080,7 @@ static void percentInverse(sqlite3_context *pCtx,int argc,sqlite3_value **argv){
}
if( p->bSorted==0 ){
assert( p->nUsed>1 );
percentSort(p->a, p->nUsed);
percentSort(p->a, p->nUsed, -1);
p->bSorted = 1;
}
p->bKeepSorted = 1;
@@ -3081,13 +3109,13 @@ static void percentCompute(sqlite3_context *pCtx, int bIsFinal){
if( p==0 ) return;
if( p->a==0 ) return;
if( p->nUsed ){
if( p->bSorted==0 ){
assert( p->nUsed>1 );
percentSort(p->a, p->nUsed);
p->bSorted = 1;
}
ix = p->rPct*(p->nUsed-1);
i1 = (unsigned)ix;
if( p->bSorted==0 ){
assert( p->nUsed>1 );
percentSort(p->a, p->nUsed, (bIsFinal ? (int)i1 : -1));
p->bSorted = 1;
}
if( settings & 1 ){
vx = p->a[i1];
}else{