queryjumblefuncs.c

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/*-------------------------------------------------------------------------
 *
 * queryjumblefuncs.c
 *   Query normalization and fingerprinting.
 *
 * Normalization is a process whereby similar queries, typically differing only
 * in their constants (though the exact rules are somewhat more subtle than
 * that) are recognized as equivalent, and are tracked as a single entry.  This
 * is particularly useful for non-prepared queries.
 *
 * Normalization is implemented by fingerprinting queries, selectively
 * serializing those fields of each query tree's nodes that are judged to be
 * essential to the query.  This is referred to as a query jumble.  This is
 * distinct from a regular serialization in that various extraneous
 * information is ignored as irrelevant or not essential to the query, such
 * as the collations of Vars and, most notably, the values of constants.
 *
 * This jumble is acquired at the end of parse analysis of each query, and
 * a 64-bit hash of it is stored into the query's Query.queryId field.
 * The server then copies this value around, making it available in plan
 * tree(s) generated from the query.  The executor can then use this value
 * to blame query costs on the proper queryId.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/nodes/queryjumblefuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "common/hashfn.h"
#include "miscadmin.h"
#include "nodes/queryjumble.h"
#include "parser/scansup.h"
 
#define JUMBLE_SIZE             1024    /* query serialization buffer size */
 
/* GUC parameters */
int         compute_query_id = COMPUTE_QUERY_ID_AUTO;
 
/*
 * True when compute_query_id is ON or AUTO, and a module requests them.
 *
 * Note that IsQueryIdEnabled() should be used instead of checking
 * query_id_enabled or compute_query_id directly when we want to know
 * whether query identifiers are computed in the core or not.
 */
bool        query_id_enabled = false;
 
static void AppendJumble(JumbleState *jstate,
                         const unsigned char *item, Size size);
static void RecordConstLocation(JumbleState *jstate, int location);
static void _jumbleNode(JumbleState *jstate, Node *node);
static void _jumbleA_Const(JumbleState *jstate, Node *node);
static void _jumbleList(JumbleState *jstate, Node *node);
static void _jumbleVariableSetStmt(JumbleState *jstate, Node *node);
 
/*
 * Given a possibly multi-statement source string, confine our attention to the
 * relevant part of the string.
 */
const char *
CleanQuerytext(const char *query, int *location, int *len)
{
    int         query_location = *location;
    int         query_len = *len;
 
    /* First apply starting offset, unless it's -1 (unknown). */
    if (query_location >= 0)
    {
        Assert(query_location <= strlen(query));
        query += query_location;
        /* Length of 0 (or -1) means "rest of string" */
        if (query_len <= 0)
            query_len = strlen(query);
        else
            Assert(query_len <= strlen(query));
    }
    else
    {
        /* If query location is unknown, distrust query_len as well */
        query_location = 0;
        query_len = strlen(query);
    }
 
    /*
     * Discard leading and trailing whitespace, too.  Use scanner_isspace()
     * not libc's isspace(), because we want to match the lexer's behavior.
     */
    while (query_len > 0 && scanner_isspace(query[0]))
        query++, query_location++, query_len--;
    while (query_len > 0 && scanner_isspace(query[query_len - 1]))
        query_len--;
 
    *location = query_location;
    *len = query_len;
 
    return query;
}
 
JumbleState *
JumbleQuery(Query *query)
{
    JumbleState *jstate = NULL;
 
    Assert(IsQueryIdEnabled());
 
    jstate = (JumbleState *) palloc(sizeof(JumbleState));
 
    /* Set up workspace for query jumbling */
    jstate->jumble = (unsigned char *) palloc(JUMBLE_SIZE);
    jstate->jumble_len = 0;
    jstate->clocations_buf_size = 32;
    jstate->clocations = (LocationLen *)
        palloc(jstate->clocations_buf_size * sizeof(LocationLen));
    jstate->clocations_count = 0;
    jstate->highest_extern_param_id = 0;
 
    /* Compute query ID and mark the Query node with it */
    _jumbleNode(jstate, (Node *) query);
    query->queryId = DatumGetUInt64(hash_any_extended(jstate->jumble,
                                                      jstate->jumble_len,
                                                      0));
 
    /*
     * If we are unlucky enough to get a hash of zero, use 1 instead for
     * normal statements and 2 for utility queries.
     */
    if (query->queryId == UINT64CONST(0))
    {
        if (query->utilityStmt)
            query->queryId = UINT64CONST(2);
        else
            query->queryId = UINT64CONST(1);
    }
 
    return jstate;
}
 
/*
 * Enables query identifier computation.
 *
 * Third-party plugins can use this function to inform core that they require
 * a query identifier to be computed.
 */
void
EnableQueryId(void)
{
    if (compute_query_id != COMPUTE_QUERY_ID_OFF)
        query_id_enabled = true;
}
 
/*
 * AppendJumble: Append a value that is substantive in a given query to
 * the current jumble.
 */
static void
AppendJumble(JumbleState *jstate, const unsigned char *item, Size size)
{
    unsigned char *jumble = jstate->jumble;
    Size        jumble_len = jstate->jumble_len;
 
    /*
     * Whenever the jumble buffer is full, we hash the current contents and
     * reset the buffer to contain just that hash value, thus relying on the
     * hash to summarize everything so far.
     */
    while (size > 0)
    {
        Size        part_size;
 
        if (jumble_len >= JUMBLE_SIZE)
        {
            uint64      start_hash;
 
            start_hash = DatumGetUInt64(hash_any_extended(jumble,
                                                          JUMBLE_SIZE, 0));
            memcpy(jumble, &start_hash, sizeof(start_hash));
            jumble_len = sizeof(start_hash);
        }
        part_size = Min(size, JUMBLE_SIZE - jumble_len);
        memcpy(jumble + jumble_len, item, part_size);
        jumble_len += part_size;
        item += part_size;
        size -= part_size;
    }
    jstate->jumble_len = jumble_len;
}
 
/*
 * Record location of constant within query string of query tree
 * that is currently being walked.
 */
static void
RecordConstLocation(JumbleState *jstate, int location)
{
    /* -1 indicates unknown or undefined location */
    if (location >= 0)
    {
        /* enlarge array if needed */
        if (jstate->clocations_count >= jstate->clocations_buf_size)
        {
            jstate->clocations_buf_size *= 2;
            jstate->clocations = (LocationLen *)
                repalloc(jstate->clocations,
                         jstate->clocations_buf_size *
                         sizeof(LocationLen));
        }
        jstate->clocations[jstate->clocations_count].location = location;
        /* initialize lengths to -1 to simplify third-party module usage */
        jstate->clocations[jstate->clocations_count].length = -1;
        jstate->clocations_count++;
    }
}
 
#define JUMBLE_NODE(item) \
    _jumbleNode(jstate, (Node *) expr->item)
#define JUMBLE_LOCATION(location) \
    RecordConstLocation(jstate, expr->location)
#define JUMBLE_FIELD(item) \
    AppendJumble(jstate, (const unsigned char *) &(expr->item), sizeof(expr->item))
#define JUMBLE_FIELD_SINGLE(item) \
    AppendJumble(jstate, (const unsigned char *) &(item), sizeof(item))
#define JUMBLE_STRING(str) \
do { \
    if (expr->str) \
        AppendJumble(jstate, (const unsigned char *) (expr->str), strlen(expr->str) + 1); \
} while(0)
 
#include "queryjumblefuncs.funcs.c"
 
static void
_jumbleNode(JumbleState *jstate, Node *node)
{
    Node       *expr = node;
 
    if (expr == NULL)
        return;
 
    /* Guard against stack overflow due to overly complex expressions */
    check_stack_depth();
 
    /*
     * We always emit the node's NodeTag, then any additional fields that are
     * considered significant, and then we recurse to any child nodes.
     */
    JUMBLE_FIELD(type);
 
    switch (nodeTag(expr))
    {
#include "queryjumblefuncs.switch.c"
 
        case T_List:
        case T_IntList:
        case T_OidList:
        case T_XidList:
            _jumbleList(jstate, expr);
            break;
 
        default:
            /* Only a warning, since we can stumble along anyway */
            elog(WARNING, "unrecognized node type: %d",
                 (int) nodeTag(expr));
            break;
    }
 
    /* Special cases to handle outside the automated code */
    switch (nodeTag(expr))
    {
        case T_Param:
            {
                Param      *p = (Param *) node;
 
                /*
                 * Update the highest Param id seen, in order to start
                 * normalization correctly.
                 */
                if (p->paramkind == PARAM_EXTERN &&
                    p->paramid > jstate->highest_extern_param_id)
                    jstate->highest_extern_param_id = p->paramid;
            }
            break;
        default:
            break;
    }
}
 
static void
_jumbleList(JumbleState *jstate, Node *node)
{
    List       *expr = (List *) node;
    ListCell   *l;
 
    switch (expr->type)
    {
        case T_List:
            foreach(l, expr)
                _jumbleNode(jstate, lfirst(l));
            break;
        case T_IntList:
            foreach(l, expr)
                JUMBLE_FIELD_SINGLE(lfirst_int(l));
            break;
        case T_OidList:
            foreach(l, expr)
                JUMBLE_FIELD_SINGLE(lfirst_oid(l));
            break;
        case T_XidList:
            foreach(l, expr)
                JUMBLE_FIELD_SINGLE(lfirst_xid(l));
            break;
        default:
            elog(ERROR, "unrecognized list node type: %d",
                 (int) expr->type);
            return;
    }
}
 
static void
_jumbleA_Const(JumbleState *jstate, Node *node)
{
    A_Const    *expr = (A_Const *) node;
 
    JUMBLE_FIELD(isnull);
    if (!expr->isnull)
    {
        JUMBLE_FIELD(val.node.type);
        switch (nodeTag(&expr->val))
        {
            case T_Integer:
                JUMBLE_FIELD(val.ival.ival);
                break;
            case T_Float:
                JUMBLE_STRING(val.fval.fval);
                break;
            case T_Boolean:
                JUMBLE_FIELD(val.boolval.boolval);
                break;
            case T_String:
                JUMBLE_STRING(val.sval.sval);
                break;
            case T_BitString:
                JUMBLE_STRING(val.bsval.bsval);
                break;
            default:
                elog(ERROR, "unrecognized node type: %d",
                     (int) nodeTag(&expr->val));
                break;
        }
    }
}
 
static void
_jumbleVariableSetStmt(JumbleState *jstate, Node *node)
{
    VariableSetStmt *expr = (VariableSetStmt *) node;
 
    JUMBLE_FIELD(kind);
    JUMBLE_STRING(name);
 
    /*
     * Account for the list of arguments in query jumbling only if told by the
     * parser.
     */
    if (expr->jumble_args)
        JUMBLE_NODE(args);
    JUMBLE_FIELD(is_local);
    JUMBLE_LOCATION(location);
}