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Overview
Comment: | Fix typos and add clarification to comments in where.c. No code changes. |
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f8d8790ede0fcaf6c5b60ac22919c1d9 |
User & Date: | drh 2013-08-07 01:18:38.449 |
Context
2013-08-07
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14:18 | Add a guard #ifndef to test_intarray.h to prevent harm if it is #included more than once. Add a comment on the closing #endif of the guards on sqlite3.h and test_multiplex.h. (check-in: 0ad83ceb79 user: drh tags: trunk) | |
01:18 | Fix typos and add clarification to comments in where.c. No code changes. (check-in: f8d8790ede user: drh tags: trunk) | |
2013-08-06
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19:18 | Fix a test case related to partial indices so that it works even if STAT3 is disabled. (check-in: 153c645025 user: drh tags: trunk) | |
Changes
Changes to src/where.c.
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29 30 31 32 33 34 35 | && (defined(SQLITE_TEST) || defined(SQLITE_ENABLE_WHERETRACE)) # define WHERETRACE(K,X) if(sqlite3WhereTrace&(K)) sqlite3DebugPrintf X # define WHERETRACE_ENABLED 1 #else # define WHERETRACE(K,X) #endif | | | 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | && (defined(SQLITE_TEST) || defined(SQLITE_ENABLE_WHERETRACE)) # define WHERETRACE(K,X) if(sqlite3WhereTrace&(K)) sqlite3DebugPrintf X # define WHERETRACE_ENABLED 1 #else # define WHERETRACE(K,X) #endif /* Forward references */ typedef struct WhereClause WhereClause; typedef struct WhereMaskSet WhereMaskSet; typedef struct WhereOrInfo WhereOrInfo; typedef struct WhereAndInfo WhereAndInfo; typedef struct WhereLevel WhereLevel; typedef struct WhereLoop WhereLoop; |
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51 52 53 54 55 56 57 | /* ** Cost X is tracked as 10*log2(X) stored in a 16-bit integer. The ** maximum cost for ordinary tables is 64*(2**63) which becomes 6900. ** (Virtual tables can return a larger cost, but let's assume they do not.) ** So all costs can be stored in a 16-bit unsigned integer without risk ** of overflow. ** | | | | | | | > | 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | /* ** Cost X is tracked as 10*log2(X) stored in a 16-bit integer. The ** maximum cost for ordinary tables is 64*(2**63) which becomes 6900. ** (Virtual tables can return a larger cost, but let's assume they do not.) ** So all costs can be stored in a 16-bit unsigned integer without risk ** of overflow. ** ** Costs are estimates, so no effort is made to compute 10*log2(X) exactly. ** Instead, a close estimate is used. Any value of X<=1 is stored as 0. ** X=2 is 10. X=3 is 16. X=1000 is 99. etc. ** ** The tool/wherecosttest.c source file implements a command-line program ** that will convert WhereCosts to integers, convert integers to WhereCosts ** and do addition and multiplication on WhereCost values. The wherecosttest ** command-line program is a useful utility to have around when working with ** this module. */ typedef unsigned short int WhereCost; /* ** This object contains information needed to implement a single nested ** loop in WHERE clause. ** |
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161 162 163 164 165 166 167 | struct WhereOrCost { Bitmask prereq; /* Prerequisites */ WhereCost rRun; /* Cost of running this subquery */ WhereCost nOut; /* Number of outputs for this subquery */ }; /* The WhereOrSet object holds a set of possible WhereOrCosts that | | | | 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 | struct WhereOrCost { Bitmask prereq; /* Prerequisites */ WhereCost rRun; /* Cost of running this subquery */ WhereCost nOut; /* Number of outputs for this subquery */ }; /* The WhereOrSet object holds a set of possible WhereOrCosts that ** correspond to the subquery(s) of OR-clause processing. Only the ** best N_OR_COST elements are retained. */ #define N_OR_COST 3 struct WhereOrSet { u16 n; /* Number of valid a[] entries */ WhereOrCost a[N_OR_COST]; /* Set of best costs */ }; |
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228 229 230 231 232 233 234 | ** use of a bitmask encoding for the operator allows us to search ** quickly for terms that match any of several different operators. ** ** A WhereTerm might also be two or more subterms connected by OR: ** ** (t1.X <op> <expr>) OR (t1.Y <op> <expr>) OR .... ** | | | | 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 | ** use of a bitmask encoding for the operator allows us to search ** quickly for terms that match any of several different operators. ** ** A WhereTerm might also be two or more subterms connected by OR: ** ** (t1.X <op> <expr>) OR (t1.Y <op> <expr>) OR .... ** ** In this second case, wtFlag has the TERM_ORINFO bit set and eOperator==WO_OR ** and the WhereTerm.u.pOrInfo field points to auxiliary information that ** is collected about the OR clause. ** ** If a term in the WHERE clause does not match either of the two previous ** categories, then eOperator==0. The WhereTerm.pExpr field is still set ** to the original subexpression content and wtFlags is set up appropriately ** but no other fields in the WhereTerm object are meaningful. ** ** When eOperator!=0, prereqRight and prereqAll record sets of cursor numbers, |
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742 743 744 745 746 747 748 | */ static void createMask(WhereMaskSet *pMaskSet, int iCursor){ assert( pMaskSet->n < ArraySize(pMaskSet->ix) ); pMaskSet->ix[pMaskSet->n++] = iCursor; } /* | | | 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 | */ static void createMask(WhereMaskSet *pMaskSet, int iCursor){ assert( pMaskSet->n < ArraySize(pMaskSet->ix) ); pMaskSet->ix[pMaskSet->n++] = iCursor; } /* ** These routines walk (recursively) an expression tree and generate ** a bitmask indicating which tables are used in that expression ** tree. */ static Bitmask exprListTableUsage(WhereMaskSet*, ExprList*); static Bitmask exprSelectTableUsage(WhereMaskSet*, Select*); static Bitmask exprTableUsage(WhereMaskSet *pMaskSet, Expr *p){ Bitmask mask = 0; |
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1259 1260 1261 1262 1263 1264 1265 | ** subsubterms at least one of which is indexable. Indexable AND ** subterms have their eOperator set to WO_AND and they have ** u.pAndInfo set to a dynamically allocated WhereAndTerm object. ** ** From another point of view, "indexable" means that the subterm could ** potentially be used with an index if an appropriate index exists. ** This analysis does not consider whether or not the index exists; that | | | | | 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 | ** subsubterms at least one of which is indexable. Indexable AND ** subterms have their eOperator set to WO_AND and they have ** u.pAndInfo set to a dynamically allocated WhereAndTerm object. ** ** From another point of view, "indexable" means that the subterm could ** potentially be used with an index if an appropriate index exists. ** This analysis does not consider whether or not the index exists; that ** is decided elsewhere. This analysis only looks at whether subterms ** appropriate for indexing exist. ** ** All examples A through E above satisfy case 2. But if a term ** also statisfies case 1 (such as B) we know that the optimizer will ** always prefer case 1, so in that case we pretend that case 2 is not ** satisfied. ** ** It might be the case that multiple tables are indexable. For example, ** (E) above is indexable on tables P, Q, and R. ** |
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1929 1930 1931 1932 1933 1934 1935 | } } return 0; } /* | | | 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 | } } return 0; } /* ** Find (an approximate) sum of two WhereCosts. This computation is ** not a simple "+" operator because WhereCost is stored as a logarithmic ** value. ** */ static WhereCost whereCostAdd(WhereCost a, WhereCost b){ static const unsigned char x[] = { 10, 10, /* 0,1 */ |
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