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Attached is an update to contrib/tablefunc. It implements a new hashed

Browse Source 
version of crosstab. This fixes a major deficiency in real-world use of
the original version. Easiest to undestand with an illustration:

Data:
-------------------------------------------------------------------
select * from cth;
  id | rowid |        rowdt        |   attribute    |      val
----+-------+---------------------+----------------+---------------
   1 | test1 | 2003-03-01 00:00:00 | temperature    | 42
   2 | test1 | 2003-03-01 00:00:00 | test_result    | PASS
   3 | test1 | 2003-03-01 00:00:00 | volts          | 2.6987
   4 | test2 | 2003-03-02 00:00:00 | temperature    | 53
   5 | test2 | 2003-03-02 00:00:00 | test_result    | FAIL
   6 | test2 | 2003-03-02 00:00:00 | test_startdate | 01 March 2003
   7 | test2 | 2003-03-02 00:00:00 | volts          | 3.1234
(7 rows)

Original crosstab:
-------------------------------------------------------------------
SELECT * FROM crosstab(
   'SELECT rowid, attribute, val FROM cth ORDER BY 1,2',4)
AS c(rowid text, temperature text, test_result text, test_startdate
text, volts text);
  rowid | temperature | test_result | test_startdate | volts
-------+-------------+-------------+----------------+--------
  test1 | 42          | PASS        | 2.6987         |
  test2 | 53          | FAIL        | 01 March 2003  | 3.1234
(2 rows)

Hashed crosstab:
-------------------------------------------------------------------
SELECT * FROM crosstab(
   'SELECT rowid, attribute, val FROM cth ORDER BY 1',
   'SELECT DISTINCT attribute FROM cth ORDER BY 1')
AS c(rowid text, temperature int4, test_result text, test_startdate
timestamp, volts float8);
  rowid | temperature | test_result |   test_startdate    | volts
-------+-------------+-------------+---------------------+--------
  test1 |          42 | PASS        |                     | 2.6987
  test2 |          53 | FAIL        | 2003-03-01 00:00:00 | 3.1234
(2 rows)

Notice that the original crosstab slides data over to the left in the
result tuple when it encounters missing data. In order to work around
this you have to be make your source sql do all sorts of contortions
(cartesian join of distinct rowid with distinct attribute; left join
that back to the real source data). The new version avoids this by
building a hash table using a second distinct attribute query.

The new version also allows for "extra" columns (see the README) and
allows the result columns to be coerced into differing datatypes if they
are suitable (as shown above).

In testing a "real-world" data set (69 distinct rowid's, 27 distinct
categories/attributes, multiple missing data points) I saw about a
5-fold improvement in execution time (from about 2200 ms old, to 440 ms
new).

I left the original version intact because: 1) BC, 2) it is probably
slightly faster if you know that you have no missing attributes.

README and regression test adjustments included. If there are no
objections, please apply.

Joe Conway
This commit is contained in:
Bruce Momjian
2003-03-20 06:46:30 +00:00
parent add932ee91
commit 64d0b8b05f
6 changed files with 655 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

403
contrib/tablefunc/tablefunc.c
View File

@ -39,6 +39,11 @@
#include "tablefunc.h"
static int load_categories_hash(char *cats_sql, MemoryContext per_query_ctx);
static Tuplestorestate *get_crosstab_tuplestore(char *sql,
int num_categories,
TupleDesc tupdesc,
MemoryContext per_query_ctx);
static void validateConnectbyTupleDesc(TupleDesc tupdesc, bool show_branch);
static bool compatCrosstabTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
static bool compatConnectbyTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
@ -95,6 +100,67 @@ typedef struct
/* sign, 10 digits, '\0' */
#define INT32_STRLEN 12
/* hash table support */
static HTAB *crosstab_HashTable;
/* The information we cache about loaded procedures */
typedef struct crosstab_cat_desc
{
char *catname;
int attidx; /* zero based */
} crosstab_cat_desc;
#define MAX_CATNAME_LEN NAMEDATALEN
#define INIT_CATS 64
#define crosstab_HashTableLookup(CATNAME, CATDESC) \
do { \
crosstab_HashEnt *hentry; char key[MAX_CATNAME_LEN]; \
\
MemSet(key, 0, MAX_CATNAME_LEN); \
snprintf(key, MAX_CATNAME_LEN - 1, "%s", CATNAME); \
hentry = (crosstab_HashEnt*) hash_search(crosstab_HashTable, \
key, HASH_FIND, NULL); \
if (hentry) \
CATDESC = hentry->catdesc; \
else \
CATDESC = NULL; \
} while(0)
#define crosstab_HashTableInsert(CATDESC) \
do { \
crosstab_HashEnt *hentry; bool found; char key[MAX_CATNAME_LEN]; \
\
MemSet(key, 0, MAX_CATNAME_LEN); \
snprintf(key, MAX_CATNAME_LEN - 1, "%s", CATDESC->catname); \
hentry = (crosstab_HashEnt*) hash_search(crosstab_HashTable, \
key, HASH_ENTER, &found); \
if (hentry == NULL) \
elog(ERROR, "out of memory in crosstab_HashTable"); \
if (found) \
elog(ERROR, "trying to use a category name more than once"); \
hentry->catdesc = CATDESC; \
} while(0)
#define crosstab_HashTableDelete(CATNAME) \
do { \
crosstab_HashEnt *hentry; char key[MAX_CATNAME_LEN]; \
\
MemSet(key, 0, MAX_CATNAME_LEN); \
snprintf(key, MAX_CATNAME_LEN - 1, "%s", CATNAME); \
hentry = (crosstab_HashEnt*) hash_search(crosstab_HashTable, \
key, HASH_REMOVE, NULL); \
if (hentry == NULL) \
elog(WARNING, "trying to delete function name that does not exist."); \
} while(0)
/* hash table */
typedef struct crosstab_hashent
{
char internal_catname[MAX_CATNAME_LEN];
crosstab_cat_desc *catdesc;
} crosstab_HashEnt;
/*
* normal_rand - return requested number of random values
* with a Gaussian (Normal) distribution.
@ -592,6 +658,341 @@ crosstab(PG_FUNCTION_ARGS)
}
}
/*
* crosstab_hash - reimplement crosstab as materialized function and
* properly deal with missing values (i.e. don't pack remaining
* values to the left)
*
* crosstab - create a crosstab of rowids and values columns from a
* SQL statement returning one rowid column, one category column,
* and one value column.
*
* e.g. given sql which produces:
*
* rowid cat value
* ------+-------+-------
* row1 cat1 val1
* row1 cat2 val2
* row1 cat4 val4
* row2 cat1 val5
* row2 cat2 val6
* row2 cat3 val7
* row2 cat4 val8
*
* crosstab returns:
* <===== values columns =====>
* rowid cat1 cat2 cat3 cat4
* ------+-------+-------+-------+-------
* row1 val1 val2 null val4
* row2 val5 val6 val7 val8
*
* NOTES:
* 1. SQL result must be ordered by 1.
* 2. The number of values columns depends on the tuple description
* of the function's declared return type.
* 2. Missing values (i.e. missing category) are filled in with nulls.
* 3. Extra values (i.e. not in category results) are skipped.
*/
PG_FUNCTION_INFO_V1(crosstab_hash);
Datum
crosstab_hash(PG_FUNCTION_ARGS)
{
char *sql = GET_STR(PG_GETARG_TEXT_P(0));
char *cats_sql = GET_STR(PG_GETARG_TEXT_P(1));
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
TupleDesc tupdesc;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
int num_categories;
/* check to see if caller supports us returning a tuplestore */
if (!rsinfo || !(rsinfo->allowedModes & SFRM_Materialize))
elog(ERROR, "crosstab: materialize mode required, but it is not "
"allowed in this context");
per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
oldcontext = MemoryContextSwitchTo(per_query_ctx);
/* get the requested return tuple description */
tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
/*
* Check to make sure we have a reasonable tuple descriptor
*
* Note we will attempt to coerce the values into whatever
* the return attribute type is and depend on the "in"
* function to complain if needed.
*/
if (tupdesc->natts < 2)
elog(ERROR, "crosstab: query-specified return tuple and " \
"crosstab function are not compatible");
/* load up the categories hash table */
num_categories = load_categories_hash(cats_sql, per_query_ctx);
/* let the caller know we're sending back a tuplestore */
rsinfo->returnMode = SFRM_Materialize;
/* now go build it */
rsinfo->setResult = get_crosstab_tuplestore(sql,
num_categories,
tupdesc,
per_query_ctx);
/*
* SFRM_Materialize mode expects us to return a NULL Datum. The actual
* tuples are in our tuplestore and passed back through
* rsinfo->setResult. rsinfo->setDesc is set to the tuple description
* that we actually used to build our tuples with, so the caller can
* verify we did what it was expecting.
*/
rsinfo->setDesc = tupdesc;
MemoryContextSwitchTo(oldcontext);
return (Datum) 0;
}
/*
* load up the categories hash table
*/
static int
load_categories_hash(char *cats_sql, MemoryContext per_query_ctx)
{
HASHCTL ctl;
int ret;
int proc;
MemoryContext SPIcontext;
int num_categories = 0;
/* initialize the category hash table */
ctl.keysize = MAX_CATNAME_LEN;
ctl.entrysize = sizeof(crosstab_HashEnt);
/*
* use INIT_CATS, defined above as a guess of how
* many hash table entries to create, initially
*/
crosstab_HashTable = hash_create("crosstab hash", INIT_CATS, &ctl, HASH_ELEM);
/* Connect to SPI manager */
if ((ret = SPI_connect()) < 0)
elog(ERROR, "load_categories_hash: SPI_connect returned %d", ret);
/* Retrieve the category name rows */
ret = SPI_exec(cats_sql, 0);
num_categories = proc = SPI_processed;
/* Check for qualifying tuples */
if ((ret == SPI_OK_SELECT) && (proc > 0))
{
SPITupleTable *spi_tuptable = SPI_tuptable;
TupleDesc spi_tupdesc = spi_tuptable->tupdesc;
int i;
/*
* The provided categories SQL query must always return one column:
* category - the label or identifier for each column
*/
if (spi_tupdesc->natts != 1)
elog(ERROR, "load_categories_hash: provided categories SQL must " \
"return 1 column of at least one row");
for (i = 0; i < proc; i++)
{
crosstab_cat_desc *catdesc;
char *catname;
HeapTuple spi_tuple;
/* get the next sql result tuple */
spi_tuple = spi_tuptable->vals[i];
/* get the category from the current sql result tuple */
catname = SPI_getvalue(spi_tuple, spi_tupdesc, 1);
SPIcontext = MemoryContextSwitchTo(per_query_ctx);
catdesc = (crosstab_cat_desc *) palloc(sizeof(crosstab_cat_desc));
catdesc->catname = catname;
catdesc->attidx = i;
/* Add the proc description block to the hashtable */
crosstab_HashTableInsert(catdesc);
MemoryContextSwitchTo(SPIcontext);
}
}
else
{
/* no qualifying tuples */
SPI_finish();
elog(ERROR, "load_categories_hash: provided categories SQL must " \
"return 1 column of at least one row");
}
if (SPI_finish() != SPI_OK_FINISH)
elog(ERROR, "load_categories_hash: SPI_finish() failed");
return num_categories;
}
/*
* create and populate the crosstab tuplestore using the provided source query
*/
static Tuplestorestate *
get_crosstab_tuplestore(char *sql,
int num_categories,
TupleDesc tupdesc,
MemoryContext per_query_ctx)
{
Tuplestorestate *tupstore;
AttInMetadata *attinmeta = TupleDescGetAttInMetadata(tupdesc);
char **values;
HeapTuple tuple;
int ret;
int proc;
MemoryContext SPIcontext;
/* initialize our tuplestore */
tupstore = tuplestore_begin_heap(true, SortMem);
/* Connect to SPI manager */
if ((ret = SPI_connect()) < 0)
elog(ERROR, "get_crosstab_tuplestore: SPI_connect returned %d", ret);
/* Now retrieve the crosstab source rows */
ret = SPI_exec(sql, 0);
proc = SPI_processed;
/* Check for qualifying tuples */
if ((ret == SPI_OK_SELECT) && (proc > 0))
{
SPITupleTable *spi_tuptable = SPI_tuptable;
TupleDesc spi_tupdesc = spi_tuptable->tupdesc;
int ncols = spi_tupdesc->natts;
char *rowid;
char *lastrowid = NULL;
int i, j;
int result_ncols;
/*
* The provided SQL query must always return at least three columns:
*
* 1. rowname the label for each row - column 1 in the final result
* 2. category the label for each value-column in the final result
* 3. value the values used to populate the value-columns
*
* If there are more than three columns, the last two are taken as
* "category" and "values". The first column is taken as "rowname".
* Additional columns (2 thru N-2) are assumed the same for the same
* "rowname", and are copied into the result tuple from the first
* time we encounter a particular rowname.
*/
if (ncols < 3)
elog(ERROR, "get_crosstab_tuplestore: provided source SQL must " \
"return at least 3 columns; a rowid, a category, " \
"and a values column");
result_ncols = (ncols - 2) + num_categories;
/* Recheck to make sure we tuple descriptor still looks reasonable */
if (tupdesc->natts != result_ncols)
elog(ERROR, "get_crosstab_tuplestore: query-specified return " \
"tuple has %d columns but crosstab returns %d",
tupdesc->natts, result_ncols);
/* allocate space */
values = (char **) palloc(result_ncols * sizeof(char *));
/* and make sure it's clear */
memset(values, '\0', result_ncols * sizeof(char *));
for (i = 0; i < proc; i++)
{
HeapTuple spi_tuple;
crosstab_cat_desc *catdesc;
char *catname;
/* get the next sql result tuple */
spi_tuple = spi_tuptable->vals[i];
/* get the rowid from the current sql result tuple */
rowid = SPI_getvalue(spi_tuple, spi_tupdesc, 1);
/* if rowid is null, skip this tuple entirely */
if (rowid == NULL)
continue;
/*
* if we're on a new output row, grab the column values up to
* column N-2 now
*/
if ((lastrowid == NULL) || (strcmp(rowid, lastrowid) != 0))
{
/*
* a new row means we need to flush the old one first,
* unless we're on the very first row
*/
if (lastrowid != NULL)
{
/* switch to appropriate context while storing the tuple */
SPIcontext = MemoryContextSwitchTo(per_query_ctx);
/* rowid changed, flush the previous output row */
tuple = BuildTupleFromCStrings(attinmeta, values);
tuplestore_puttuple(tupstore, tuple);
for (j = 0; j < result_ncols; j++)
xpfree(values[j]);
/* now reset the context */
MemoryContextSwitchTo(SPIcontext);
}
values[0] = rowid;
for (j = 1; j < ncols - 2; j++)
values[j] = SPI_getvalue(spi_tuple, spi_tupdesc, j + 1);
}
/* look up the category and fill in the appropriate column */
catname = SPI_getvalue(spi_tuple, spi_tupdesc, ncols - 1);
if (catname != NULL)
{
crosstab_HashTableLookup(catname, catdesc);
if (catdesc)
values[catdesc->attidx + ncols - 2] =
SPI_getvalue(spi_tuple, spi_tupdesc, ncols);
}
xpfree(lastrowid);
lastrowid = pstrdup(rowid);
}
/* switch to appropriate context while storing the tuple */
SPIcontext = MemoryContextSwitchTo(per_query_ctx);
/* flush the last output row */
tuple = BuildTupleFromCStrings(attinmeta, values);
tuplestore_puttuple(tupstore, tuple);
/* now reset the context */
MemoryContextSwitchTo(SPIcontext);
}
else
{
/* no qualifying tuples */
SPI_finish();
}
if (SPI_finish() != SPI_OK_FINISH)
elog(ERROR, "get_crosstab_tuplestore: SPI_finish() failed");
tuplestore_donestoring(tupstore);
return tupstore;
}
/*
* connectby_text - produce a result set from a hierarchical (parent/child)
* table.
@ -668,7 +1069,7 @@ connectby_text(PG_FUNCTION_ARGS)
attinmeta = TupleDescGetAttInMetadata(tupdesc);
/* check to see if caller supports us returning a tuplestore */
if (!rsinfo->allowedModes & SFRM_Materialize)
if (!rsinfo || !(rsinfo->allowedModes & SFRM_Materialize))
elog(ERROR, "connectby requires Materialize mode, but it is not "
"allowed in this context");