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Work toward reducing the incremental size of an ExprList object to 24-byte

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per entry, from 32-bytes (on a 64-bit machine).  This helps the new
mini-lookaside allocator to run better by avoiding excessive reallocs.
The current change mostly works, but still has a few loose ends to tie up.
This check-in is merely a snapshot to save my work.

FossilOrigin-Name: fdda76cfb01bf2b19522ac4558b443634d28a69b0828677c42682b645eae1f3b
This commit is contained in:
drh
2019-12-12 22:11:33 +00:00
parent c947d6a4dc
commit cbb9da337e
6 changed files with 54 additions and 39 deletions
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30
src/sqliteInt.h
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@@ -2650,23 +2650,28 @@ struct Expr {
** also be used as the argument to a function, in which case the a.zName
** field is not used.
**
** By default the Expr.zSpan field holds a human-readable description of
** the expression that is used in the generation of error messages and
** column labels. In this case, Expr.zSpan is typically the text of a
** column expression as it exists in a SELECT statement. However, if
** the bSpanIsTab flag is set, then zSpan is overloaded to mean the name
** of the result column in the form: DATABASE.TABLE.COLUMN. This later
** form is used for name resolution with nested FROM clauses.
** In order to try to keep memory usage down, the Expr.a.zEName field
** is used for multiple purposes:
**
** bNameIsTab bNameIsSpan Usage
** ---------- ----------- -------------------------
** false false (1) the AS of result set column
** (2) COLUMN= of an UPDATE
**
** true false DB.TABLE.NAME used to resolve names
** of subqueries
**
** false true Text of the original result set
** expression.
*/
struct ExprList {
int nExpr; /* Number of expressions on the list */
struct ExprList_item { /* For each expression in the list */
Expr *pExpr; /* The parse tree for this expression */
char *zEName; /* Token associated with this expression */
char *zSpan; /* Original text of the expression */
u8 sortFlags; /* Mask of KEYINFO_ORDER_* flags */
unsigned eEName :2; /* Meaning of zEName */
unsigned done :1; /* A flag to indicate when processing is finished */
unsigned bSpanIsTab :1; /* zSpan holds DB.TABLE.COLUMN */
unsigned reusable :1; /* Constant expression is reusable */
unsigned bSorterRef :1; /* Defer evaluation until after sorting */
unsigned bNulls: 1; /* True if explicit "NULLS FIRST/LAST" */
@@ -2680,6 +2685,13 @@ struct ExprList {
} a[1]; /* One slot for each expression in the list */
};
/*
** Allowed values for Expr.a.eEName
*/
#define ENAME_NAME 0 /* The AS clause of a result set */
#define ENAME_SPAN 1 /* Complete text of the result set expression */
#define ENAME_TAB 2 /* "DB.TABLE.NAME" for the result set */
/*
** An instance of this structure can hold a simple list of identifiers,
** such as the list "a,b,c" in the following statements: