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Performance improvement for libpq: avoid calling malloc separately

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for each field of each tuple.  Makes more difference than you'd think...
This commit is contained in:
Tom Lane 1998-11-18 00:47:28 +00:00
parent 643c7beddf
commit fd0366e1b5
2 changed files with 283 additions and 116 deletions
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335
src/interfaces/libpq/fe-exec.c
View File

@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.69 1998/10/01 01:40:21 tgl Exp $
* $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.70 1998/11/18 00:47:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -28,10 +28,6 @@
#include <ctype.h>
/* the rows array in a PGresGroup has to grow to accommodate the rows */
/* returned. Each time, we grow by this much: */
#define TUPARR_GROW_BY 100
/* keep this in same order as ExecStatusType in libpq-fe.h */
const char *const pgresStatus[] = {
"PGRES_EMPTY_QUERY",
@ -49,7 +45,6 @@ const char *const pgresStatus[] = {
((*(conn)->noticeHook) ((conn)->noticeArg, (message)))
static void freeTuple(PGresAttValue *tuple, int numAttributes);
static int addTuple(PGresult *res, PGresAttValue *tup);
static void parseInput(PGconn *conn);
static int getRowDescriptions(PGconn *conn);
@ -58,6 +53,63 @@ static int getNotify(PGconn *conn);
static int getNotice(PGconn *conn);
/* ----------------
* Space management for PGresult.
*
* Formerly, libpq did a separate malloc() for each field of each tuple
* returned by a query. This was remarkably expensive --- malloc/free
* consumed a sizable part of the application's runtime. And there is
* no real need to keep track of the fields separately, since they will
* all be freed together when the PGresult is released. So now, we grab
* large blocks of storage from malloc and allocate space for query data
* within these blocks, using a trivially simple allocator. This reduces
* the number of malloc/free calls dramatically, and it also avoids
* fragmentation of the malloc storage arena.
* The PGresult structure itself is still malloc'd separately. We could
* combine it with the first allocation block, but that would waste space
* for the common case that no extra storage is actually needed (that is,
* the SQL command did not return tuples).
* We also malloc the top-level array of tuple pointers separately, because
* we need to be able to enlarge it via realloc, and our trivial space
* allocator doesn't handle that effectively. (Too bad the FE/BE protocol
* doesn't tell us up front how many tuples will be returned.)
* All other subsidiary storage for a PGresult is kept in PGresult_data blocks
* of size PGRESULT_DATA_BLOCKSIZE. The overhead at the start of each block
* is just a link to the next one, if any. Free-space management info is
* kept in the owning PGresult.
* A query returning a small amount of data will thus require three malloc
* calls: one for the PGresult, one for the tuples pointer array, and one
* PGresult_data block.
* Only the most recently allocated PGresult_data block is a candidate to
* have more stuff added to it --- any extra space left over in older blocks
* is wasted. We could be smarter and search the whole chain, but the point
* here is to be simple and fast. Typical applications do not keep a PGresult
* around very long anyway, so some wasted space within one is not a problem.
*
* Tuning constants for the space allocator are:
* PGRESULT_DATA_BLOCKSIZE: size of a standard allocation block, in bytes
* PGRESULT_ALIGN_BOUNDARY: assumed alignment requirement for binary data
* PGRESULT_SEP_ALLOC_THRESHOLD: objects bigger than this are given separate
* blocks, instead of being crammed into a regular allocation block.
* Requirements for correct function are:
* PGRESULT_ALIGN_BOUNDARY >= sizeof(pointer)
* to ensure the initial pointer in a block is not overwritten.
* PGRESULT_ALIGN_BOUNDARY must be a multiple of the alignment requirements
* of all machine data types.
* PGRESULT_SEP_ALLOC_THRESHOLD + PGRESULT_ALIGN_BOUNDARY <=
* PGRESULT_DATA_BLOCKSIZE
* pqResultAlloc assumes an object smaller than the threshold will fit
* in a new block.
* The amount of space wasted at the end of a block could be as much as
* PGRESULT_SEP_ALLOC_THRESHOLD, so it doesn't pay to make that too large.
* ----------------
*/
#define PGRESULT_DATA_BLOCKSIZE 2048
#define PGRESULT_ALIGN_BOUNDARY 16 /* 8 is probably enough, really */
#define PGRESULT_SEP_ALLOC_THRESHOLD (PGRESULT_DATA_BLOCKSIZE / 2)
/*
* PQmakeEmptyPGresult
* returns a newly allocated, initialized PGresult with given status.
@ -76,7 +128,7 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
result = (PGresult *) malloc(sizeof(PGresult));
result->conn = conn; /* should go away eventually */
result->conn = conn; /* might be NULL */
result->ntups = 0;
result->numAttributes = 0;
result->attDescs = NULL;
@ -86,6 +138,11 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
result->cmdStatus[0] = '\0';
result->binary = 0;
result->errMsg = NULL;
result->null_field[0] = '\0';
result->curBlock = NULL;
result->curOffset = 0;
result->spaceLeft = 0;
if (conn) /* consider copying conn's errorMessage */
{
switch (status)
@ -105,6 +162,117 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
return result;
}
/*
* pqResultAlloc -
* Allocate subsidiary storage for a PGresult.
*
* nBytes is the amount of space needed for the object.
* If isBinary is true, we assume that we need to align the object on
* a machine allocation boundary.
* If isBinary is false, we assume the object is a char string and can
* be allocated on any byte boundary.
*/
void *
pqResultAlloc(PGresult *res, int nBytes, int isBinary)
{
char *space;
PGresult_data *block;
if (! res)
return NULL;
if (nBytes <= 0)
return res->null_field;
/* If alignment is needed, round up the current position to an
* alignment boundary.
*/
if (isBinary)
{
int offset = res->curOffset % PGRESULT_ALIGN_BOUNDARY;
if (offset)
{
res->curOffset += PGRESULT_ALIGN_BOUNDARY - offset;
res->spaceLeft -= PGRESULT_ALIGN_BOUNDARY - offset;
}
}
/* If there's enough space in the current block, no problem. */
if (nBytes <= res->spaceLeft)
{
space = res->curBlock->space + res->curOffset;
res->curOffset += nBytes;
res->spaceLeft -= nBytes;
return space;
}
/* If the requested object is very large, give it its own block; this
* avoids wasting what might be most of the current block to start a new
* block. (We'd have to special-case requests bigger than the block size
* anyway.) The object is always given binary alignment in this case.
*/
if (nBytes >= PGRESULT_SEP_ALLOC_THRESHOLD)
{
block = (PGresult_data *) malloc(nBytes + PGRESULT_ALIGN_BOUNDARY);
if (! block)
return NULL;
space = block->space + PGRESULT_ALIGN_BOUNDARY;
if (res->curBlock)
{
/* Tuck special block below the active block, so that we don't
* have to waste the free space in the active block.
*/
block->next = res->curBlock->next;
res->curBlock->next = block;
}
else
{
/* Must set up the new block as the first active block. */
block->next = NULL;
res->curBlock = block;
res->spaceLeft = 0; /* be sure it's marked full */
}
return space;
}
/* Otherwise, start a new block. */
block = (PGresult_data *) malloc(PGRESULT_DATA_BLOCKSIZE);
if (! block)
return NULL;
block->next = res->curBlock;
res->curBlock = block;
if (isBinary)
{
/* object needs full alignment */
res->curOffset = PGRESULT_ALIGN_BOUNDARY;
res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - PGRESULT_ALIGN_BOUNDARY;
}
else
{
/* we can cram it right after the overhead pointer */
res->curOffset = sizeof(PGresult_data);
res->spaceLeft = PGRESULT_DATA_BLOCKSIZE - sizeof(PGresult_data);
}
space = block->space + res->curOffset;
res->curOffset += nBytes;
res->spaceLeft -= nBytes;
return space;
}
/*
* pqResultStrdup -
* Like strdup, but the space is subsidiary PGresult space.
*/
char *
pqResultStrdup(PGresult *res, const char *str)
{
char *space = (char*) pqResultAlloc(res, strlen(str)+1, FALSE);
if (space)
strcpy(space, str);
return space;
}
/*
* pqSetResultError -
* assign a new error message to a PGresult
@ -114,11 +282,10 @@ pqSetResultError(PGresult *res, const char *msg)
{
if (!res)
return;
if (res->errMsg)
free(res->errMsg);
res->errMsg = NULL;
if (msg && *msg)
res->errMsg = strdup(msg);
res->errMsg = pqResultStrdup(res, msg);
else
res->errMsg = NULL;
}
/*
@ -128,58 +295,25 @@ pqSetResultError(PGresult *res, const char *msg)
void
PQclear(PGresult *res)
{
int i;
PGresult_data *block;
if (!res)
return;
/* free all the rows */
/* Free all the subsidiary blocks */
while ((block = res->curBlock) != NULL) {
res->curBlock = block->next;
free(block);
}
/* Free the top-level tuple pointer array */
if (res->tuples)
{
for (i = 0; i < res->ntups; i++)
freeTuple(res->tuples[i], res->numAttributes);
free(res->tuples);
}
/* free all the attributes */
if (res->attDescs)
{
for (i = 0; i < res->numAttributes; i++)
{
if (res->attDescs[i].name)
free(res->attDescs[i].name);
}
free(res->attDescs);
}
/* free the error text */
if (res->errMsg)
free(res->errMsg);
/* free the structure itself */
/* Free the PGresult structure itself */
free(res);
}
/*
* Free a single tuple structure.
*/
static void
freeTuple(PGresAttValue *tuple, int numAttributes)
{
int i;
if (tuple)
{
for (i = 0; i < numAttributes; i++)
{
if (tuple[i].value)
free(tuple[i].value);
}
free(tuple);
}
}
/*
* Handy subroutine to deallocate any partially constructed async result.
*/
@ -187,13 +321,8 @@ freeTuple(PGresAttValue *tuple, int numAttributes)
void
pqClearAsyncResult(PGconn *conn)
{
/* Get rid of incomplete result and any not-yet-added tuple */
if (conn->result)
{
if (conn->curTuple)
freeTuple(conn->curTuple, conn->result->numAttributes);
PQclear(conn->result);
}
conn->result = NULL;
conn->curTuple = NULL;
}
@ -201,7 +330,7 @@ pqClearAsyncResult(PGconn *conn)
/*
* addTuple
* add a row to the PGresult structure, growing it if necessary
* add a row pointer to the PGresult structure, growing it if necessary
* Returns TRUE if OK, FALSE if not enough memory to add the row
*/
static int
@ -220,7 +349,7 @@ addTuple(PGresult *res, PGresAttValue *tup)
* Note that the positions beyond res->ntups are garbage, not
* necessarily NULL.
*/
int newSize = res->tupArrSize + TUPARR_GROW_BY;
int newSize = (res->tupArrSize > 0) ? res->tupArrSize * 2 : 128;
PGresAttValue ** newTuples = (PGresAttValue **)
realloc(res->tuples, newSize * sizeof(PGresAttValue *));
if (! newTuples)
@ -564,7 +693,7 @@ getRowDescriptions(PGconn *conn)
if (nfields > 0)
{
result->attDescs = (PGresAttDesc *)
malloc(nfields * sizeof(PGresAttDesc));
pqResultAlloc(result, nfields * sizeof(PGresAttDesc), TRUE);
MemSet((char *) result->attDescs, 0, nfields * sizeof(PGresAttDesc));
}
@ -574,7 +703,7 @@ getRowDescriptions(PGconn *conn)
char typName[MAX_MESSAGE_LEN];
int typid;
int typlen;
int atttypmod = -1;
int atttypmod;
if (pqGets(typName, MAX_MESSAGE_LEN, conn) ||
pqGetInt(&typid, 4, conn) ||
@ -594,7 +723,7 @@ getRowDescriptions(PGconn *conn)
*/
if (typlen == 0xFFFF)
typlen = -1;
result->attDescs[i].name = strdup(typName);
result->attDescs[i].name = pqResultStrdup(result, typName);
result->attDescs[i].typid = typid;
result->attDescs[i].typlen = typlen;
result->attDescs[i].atttypmod = atttypmod;
@ -618,7 +747,8 @@ getRowDescriptions(PGconn *conn)
static int
getAnotherTuple(PGconn *conn, int binary)
{
int nfields = conn->result->numAttributes;
PGresult *result = conn->result;
int nfields = result->numAttributes;
PGresAttValue *tup;
char bitmap[MAX_FIELDS]; /* the backend sends us a bitmap
* of which attributes are null */
@ -629,13 +759,13 @@ getAnotherTuple(PGconn *conn, int binary)
int bitcnt; /* number of bits examined in current byte */
int vlen; /* length of the current field value */
conn->result->binary = binary;
result->binary = binary;
/* Allocate tuple space if first time for this data message */
if (conn->curTuple == NULL)
{
conn->curTuple = (PGresAttValue *)
malloc(nfields * sizeof(PGresAttValue));
pqResultAlloc(result, nfields * sizeof(PGresAttValue), TRUE);
if (conn->curTuple == NULL)
goto outOfMemory;
MemSet((char *) conn->curTuple, 0, nfields * sizeof(PGresAttValue));
@ -670,12 +800,7 @@ getAnotherTuple(PGconn *conn, int binary)
if (!(bmap & 0200))
{
/* if the field value is absent, make it a null string */
if (tup[i].value == NULL)
{
tup[i].value = strdup("");
if (tup[i].value == NULL)
goto outOfMemory;
}
tup[i].value = result->null_field;
tup[i].len = NULL_LEN;
}
else
@ -689,7 +814,7 @@ getAnotherTuple(PGconn *conn, int binary)
vlen = 0;
if (tup[i].value == NULL)
{
tup[i].value = (char *) malloc(vlen + 1);
tup[i].value = (char *) pqResultAlloc(result, vlen+1, binary);
if (tup[i].value == NULL)
goto outOfMemory;
}
@ -714,14 +839,8 @@ getAnotherTuple(PGconn *conn, int binary)
}
/* Success! Store the completed tuple in the result */
if (! addTuple(conn->result, tup))
{
/* Oops, not enough memory to add the tuple to conn->result,
* so must free it ourselves...
*/
freeTuple(tup, nfields);
if (! addTuple(result, tup))
goto outOfMemory;
}
/* and reset for a new message */
conn->curTuple = NULL;
return 0;
@ -1437,10 +1556,13 @@ check_field_number(const char *routineName, PGresult *res, int field_num)
return FALSE; /* no way to display error message... */
if (field_num < 0 || field_num >= res->numAttributes)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! field number %d is out of range 0..%d\n",
routineName, field_num, res->numAttributes - 1);
DONOTICE(res->conn, res->conn->errorMessage);
if (res->conn)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! field number %d is out of range 0..%d\n",
routineName, field_num, res->numAttributes - 1);
DONOTICE(res->conn, res->conn->errorMessage);
}
return FALSE;
}
return TRUE;
@ -1454,18 +1576,24 @@ check_tuple_field_number(const char *routineName, PGresult *res,
return FALSE; /* no way to display error message... */
if (tup_num < 0 || tup_num >= res->ntups)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! tuple number %d is out of range 0..%d\n",
routineName, tup_num, res->ntups - 1);
DONOTICE(res->conn, res->conn->errorMessage);
if (res->conn)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! tuple number %d is out of range 0..%d\n",
routineName, tup_num, res->ntups - 1);
DONOTICE(res->conn, res->conn->errorMessage);
}
return FALSE;
}
if (field_num < 0 || field_num >= res->numAttributes)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! field number %d is out of range 0..%d\n",
routineName, field_num, res->numAttributes - 1);
DONOTICE(res->conn, res->conn->errorMessage);
if (res->conn)
{
sprintf(res->conn->errorMessage,
"%s: ERROR! field number %d is out of range 0..%d\n",
routineName, field_num, res->numAttributes - 1);
DONOTICE(res->conn, res->conn->errorMessage);
}
return FALSE;
}
return TRUE;
@ -1635,10 +1763,13 @@ PQcmdTuples(PGresult *res)
if (*p == 0)
{
sprintf(res->conn->errorMessage,
"PQcmdTuples (%s) -- bad input from server\n",
res->cmdStatus);
DONOTICE(res->conn, res->conn->errorMessage);
if (res->conn)
{
sprintf(res->conn->errorMessage,
"PQcmdTuples (%s) -- bad input from server\n",
res->cmdStatus);
DONOTICE(res->conn, res->conn->errorMessage);
}
return "";
}
p++;
@ -1648,9 +1779,12 @@ PQcmdTuples(PGresult *res)
p++; /* INSERT: skip oid */
if (*p == 0)
{
sprintf(res->conn->errorMessage,
"PQcmdTuples (INSERT) -- there's no # of tuples\n");
DONOTICE(res->conn, res->conn->errorMessage);
if (res->conn)
{
sprintf(res->conn->errorMessage,
"PQcmdTuples (INSERT) -- there's no # of tuples\n");
DONOTICE(res->conn, res->conn->errorMessage);
}
return "";
}
p++;
@ -1680,7 +1814,8 @@ PQgetvalue(PGresult *res, int tup_num, int field_num)
/* PQgetlength:
returns the length of a field value in bytes. If res is binary,
i.e. a result of a binary portal, then the length returned does
NOT include the size field of the varlena.
NOT include the size field of the varlena. (The data returned
by PQgetvalue doesn't either.)
*/
int
PQgetlength(PGresult *res, int tup_num, int field_num)

64
src/interfaces/libpq/libpq-int.h
View File

@ -11,7 +11,7 @@
*
* Copyright (c) 1994, Regents of the University of California
*
* $Id: libpq-int.h,v 1.4 1998/10/01 01:40:25 tgl Exp $
* $Id: libpq-int.h,v 1.5 1998/11/18 00:47:26 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -49,12 +49,29 @@
#define ERROR_MSG_LENGTH 4096
#define CMDSTATUS_LEN 40
/* PGresult and the subsidiary types PGresAttDesc, PGresAttValue
/*
* PGresult and the subsidiary types PGresAttDesc, PGresAttValue
* represent the result of a query (or more precisely, of a single SQL
* command --- a query string given to PQexec can contain multiple commands).
* Note we assume that a single command can return at most one tuple group,
* hence there is no need for multiple descriptor sets.
*/
/* Subsidiary-storage management structure for PGresult.
* See space management routines in fe-exec.c for details.
* Note that space[k] refers to the k'th byte starting from the physical
* head of the block.
*/
typedef union pgresult_data PGresult_data;
union pgresult_data
{
PGresult_data *next; /* link to next block, or NULL */
char space[1]; /* dummy for accessing block as bytes */
};
/* Data about a single attribute (column) of a query result */
typedef struct pgresAttDesc
{
char *name; /* type name */
@ -63,11 +80,20 @@
int atttypmod; /* type-specific modifier info */
} PGresAttDesc;
/* use char* for Attribute values,
ASCII tuples are guaranteed to be null-terminated
For binary tuples, the first four bytes of the value is the size,
and the bytes afterwards are the value. The binary value is
not guaranteed to be null-terminated. In fact, it can have embedded nulls
/* Data for a single attribute of a single tuple */
/* We use char* for Attribute values.
The value pointer always points to a null-terminated area; we add a
null (zero) byte after whatever the backend sends us. This is only
particularly useful for ASCII tuples ... with a binary value, the
value might have embedded nulls, so the application can't use C string
operators on it. But we add a null anyway for consistency.
Note that the value itself does not contain a length word.
A NULL attribute is a special case in two ways: its len field is NULL_LEN
and its value field points to null_field in the owning PGresult. All the
NULL attributes in a query result point to the same place (there's no need
to store a null string separately for each one).
*/
#define NULL_LEN (-1) /* pg_result len for NULL value */
@ -75,7 +101,7 @@
typedef struct pgresAttValue
{
int len; /* length in bytes of the value */
char *value; /* actual value */
char *value; /* actual value, plus terminating zero byte */
} PGresAttValue;
struct pg_result
@ -91,15 +117,19 @@
* last insert query */
int binary; /* binary tuple values if binary == 1,
* otherwise ASCII */
/* NOTE: conn is kept here only for the temporary convenience of
* applications that rely on it being here. It will go away in a
* future release, because relying on it is a bad idea --- what if
* the PGresult has outlived the PGconn? About the only thing it was
* really good for was fetching the errorMessage, and we stash that
* here now anyway.
*/
PGconn *conn; /* connection we did the query on */
PGconn *conn; /* connection we did the query on, if any */
char *errMsg; /* error message, or NULL if no error */
/* All NULL attributes in the query result point to this null string */
char null_field[1];
/* Space management information. Note that attDescs and errMsg,
* if not null, point into allocated blocks. But tuples points
* to a separately malloc'd block, so that we can realloc it.
*/
PGresult_data *curBlock; /* most recently allocated block */
int curOffset; /* start offset of free space in block */
int spaceLeft; /* number of free bytes remaining in block */
};
/* PGAsyncStatusType defines the state of the query-execution state machine */
@ -202,6 +232,8 @@ extern int pqPacketSend(PGconn *conn, const char *buf, size_t len);
/* === in fe-exec.c === */
extern void pqSetResultError(PGresult *res, const char *msg);
extern void * pqResultAlloc(PGresult *res, int nBytes, int isBinary);
extern char * pqResultStrdup(PGresult *res, const char *str);
extern void pqClearAsyncResult(PGconn *conn);
/* === in fe-misc.c === */