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Begin an experimental refactoring to estimate the average number of bytes

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in table and index rows and to use that information in query planner.
Begin by renaming WhereCost to LogEst and making that type and its
conversion routines available outside of where.c.

FossilOrigin-Name: 66c4a251d61582b47d5cbe50cbca160a9209bd06
This commit is contained in:
drh
2013-10-05 18:16:02 +00:00
parent 6919b07556
commit bf539c4d5c
6 changed files with 239 additions and 199 deletions
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35
src/sqliteInt.h
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@@ -470,6 +470,31 @@ typedef INT8_TYPE i8; /* 1-byte signed integer */
typedef u32 tRowcnt; /* 32-bit is the default */
#endif
/*
** Estimated quantities used for query planning are stored as 16-bit
** logarithms. For quantity X, the value stored is 10*log2(X). This
** gives a possible range of values of approximately 1.0e986 to 1e-986.
** But the allowed values are "grainy". Not every value is representable.
** For example, quantities 16 and 17 are both represented by a LogEst
** of 40. However, since LogEst quantatites are suppose to be estimates,
** not exact values, this imprecision is not a problem.
**
** "LogEst" is short for "Logarithimic Estimate".
**
** Examples:
** 1 -> 0 20 -> 43 10000 -> 132
** 2 -> 10 25 -> 46 25000 -> 146
** 3 -> 16 100 -> 66 1000000 -> 199
** 4 -> 20 1000 -> 99 1048576 -> 200
** 10 -> 33 1024 -> 100 4294967296 -> 320
**
** The LogEst can be negative to indicate fractional values.
** Examples:
**
** 0.5 -> -10 0.1 -> -33 0.0625 -> -40
*/
typedef INT16_TYPE LogEst;
/*
** Macros to determine whether the machine is big or little endian,
** evaluated at runtime.
@@ -1362,6 +1387,7 @@ struct Table {
i16 iPKey; /* If not negative, use aCol[iPKey] as the primary key */
i16 nCol; /* Number of columns in this table */
u16 nRef; /* Number of pointers to this Table */
LogEst szTabRow; /* Estimated size of each table row in bytes */
u8 tabFlags; /* Mask of TF_* values */
u8 keyConf; /* What to do in case of uniqueness conflict on iPKey */
#ifndef SQLITE_OMIT_ALTERTABLE
@@ -1560,9 +1586,10 @@ struct Index {
char **azColl; /* Array of collation sequence names for index */
Expr *pPartIdxWhere; /* WHERE clause for partial indices */
int tnum; /* DB Page containing root of this index */
LogEst szIdxRow; /* Estimated average row size in bytes */
u16 nColumn; /* Number of columns in table used by this index */
u8 iScanRatio; /* Scan rate relative to the main table */
unsigned onError:4; /* OE_Abort, OE_Ignore, OE_Replace, or OE_None */
u8 onError; /* OE_Abort, OE_Ignore, OE_Replace, or OE_None */
unsigned autoIndex:2; /* 1==UNIQUE, 2==PRIMARY KEY, 0==CREATE INDEX */
unsigned bUnordered:1; /* Use this index for == or IN queries only */
unsigned uniqNotNull:1; /* True if UNIQUE and NOT NULL for all columns */
@@ -2967,6 +2994,12 @@ int sqlite3Atoi(const char*);
int sqlite3Utf16ByteLen(const void *pData, int nChar);
int sqlite3Utf8CharLen(const char *pData, int nByte);
u32 sqlite3Utf8Read(const u8**);
LogEst sqlite3LogEst(u64);
LogEst sqlite3LogEstAdd(LogEst,LogEst);
#ifndef SQLITE_OMIT_VIRTUALTABLE
LogEst sqlite3LogEstFromDouble(double);
#endif
u64 sqlite3LogEstToInt(LogEst);
/*
** Routines to read and write variable-length integers. These used to