/*------------------------------------------------------------------------- * * pg_stat_statements.c * * Part of pg_stat_statements.c in PostgreSQL 10. * * Copyright (c) 2008-2023, PostgreSQL Global Development Group * *------------------------------------------------------------------------- */ #include "postgres.h" #include "parser/scanner.h" static char *generate_normalized_query(JumbleState *jstate, const char *query, int query_loc, int *query_len_p); static void fill_in_constant_lengths(JumbleState *jstate, const char *query, int query_loc); static int comp_location(const void *a, const void *b); /* * Generate a normalized version of the query string that will be used to * represent all similar queries. * * Note that the normalized representation may well vary depending on * just which "equivalent" query is used to create the hashtable entry. * We assume this is OK. * * If query_loc > 0, then "query" has been advanced by that much compared to * the original string start, so we need to translate the provided locations * to compensate. (This lets us avoid re-scanning statements before the one * of interest, so it's worth doing.) * * *query_len_p contains the input string length, and is updated with * the result string length on exit. The resulting string might be longer * or shorter depending on what happens with replacement of constants. * * Returns a palloc'd string. */ static char * generate_normalized_query(JumbleState *jstate, const char *query, int query_loc, int *query_len_p) { char *norm_query; int query_len = *query_len_p; int i, norm_query_buflen, /* Space allowed for norm_query */ len_to_wrt, /* Length (in bytes) to write */ quer_loc = 0, /* Source query byte location */ n_quer_loc = 0, /* Normalized query byte location */ last_off = 0, /* Offset from start for previous tok */ last_tok_len = 0; /* Length (in bytes) of that tok */ /* * Get constants' lengths (core system only gives us locations). Note * this also ensures the items are sorted by location. */ fill_in_constant_lengths(jstate, query, query_loc); /* * Allow for $n symbols to be longer than the constants they replace. * Constants must take at least one byte in text form, while a $n symbol * certainly isn't more than 11 bytes, even if n reaches INT_MAX. We * could refine that limit based on the max value of n for the current * query, but it hardly seems worth any extra effort to do so. */ norm_query_buflen = query_len + jstate->clocations_count * 10; /* Allocate result buffer */ norm_query = palloc(norm_query_buflen + 1); for (i = 0; i < jstate->clocations_count; i++) { int off, /* Offset from start for cur tok */ tok_len; /* Length (in bytes) of that tok */ off = jstate->clocations[i].location; /* Adjust recorded location if we're dealing with partial string */ off -= query_loc; tok_len = jstate->clocations[i].length; if (tok_len < 0) continue; /* ignore any duplicates */ /* Copy next chunk (what precedes the next constant) */ len_to_wrt = off - last_off; len_to_wrt -= last_tok_len; Assert(len_to_wrt >= 0); memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt); n_quer_loc += len_to_wrt; /* And insert a param symbol in place of the constant token */ /* !!! START: HERE IS THE PART WHICH IS MODIFIED FOR PG_HINT_PLAN !!! */ n_quer_loc += sprintf(norm_query + n_quer_loc, "?"); /* !!! END: HERE IS THE PART WHICH IS MODIFIED FOR PG_HINT_PLAN !!! */ quer_loc = off + tok_len; last_off = off; last_tok_len = tok_len; } /* * We've copied up until the last ignorable constant. Copy over the * remaining bytes of the original query string. */ len_to_wrt = query_len - quer_loc; Assert(len_to_wrt >= 0); memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt); n_quer_loc += len_to_wrt; Assert(n_quer_loc <= norm_query_buflen); norm_query[n_quer_loc] = '\0'; *query_len_p = n_quer_loc; return norm_query; } /* * Given a valid SQL string and an array of constant-location records, * fill in the textual lengths of those constants. * * The constants may use any allowed constant syntax, such as float literals, * bit-strings, single-quoted strings and dollar-quoted strings. This is * accomplished by using the public API for the core scanner. * * It is the caller's job to ensure that the string is a valid SQL statement * with constants at the indicated locations. Since in practice the string * has already been parsed, and the locations that the caller provides will * have originated from within the authoritative parser, this should not be * a problem. * * Duplicate constant pointers are possible, and will have their lengths * marked as '-1', so that they are later ignored. (Actually, we assume the * lengths were initialized as -1 to start with, and don't change them here.) * * If query_loc > 0, then "query" has been advanced by that much compared to * the original string start, so we need to translate the provided locations * to compensate. (This lets us avoid re-scanning statements before the one * of interest, so it's worth doing.) * * N.B. There is an assumption that a '-' character at a Const location begins * a negative numeric constant. This precludes there ever being another * reason for a constant to start with a '-'. */ static void fill_in_constant_lengths(JumbleState *jstate, const char *query, int query_loc) { LocationLen *locs; core_yyscan_t yyscanner; core_yy_extra_type yyextra; core_YYSTYPE yylval; YYLTYPE yylloc; int last_loc = -1; int i; /* * Sort the records by location so that we can process them in order while * scanning the query text. */ if (jstate->clocations_count > 1) qsort(jstate->clocations, jstate->clocations_count, sizeof(LocationLen), comp_location); locs = jstate->clocations; /* initialize the flex scanner --- should match raw_parser() */ yyscanner = scanner_init(query, &yyextra, &ScanKeywords, ScanKeywordTokens); /* we don't want to re-emit any escape string warnings */ yyextra.escape_string_warning = false; /* Search for each constant, in sequence */ for (i = 0; i < jstate->clocations_count; i++) { int loc = locs[i].location; int tok; /* Adjust recorded location if we're dealing with partial string */ loc -= query_loc; Assert(loc >= 0); if (loc <= last_loc) continue; /* Duplicate constant, ignore */ /* Lex tokens until we find the desired constant */ for (;;) { tok = core_yylex(&yylval, &yylloc, yyscanner); /* We should not hit end-of-string, but if we do, behave sanely */ if (tok == 0) break; /* out of inner for-loop */ /* * We should find the token position exactly, but if we somehow * run past it, work with that. */ if (yylloc >= loc) { if (query[loc] == '-') { /* * It's a negative value - this is the one and only case * where we replace more than a single token. * * Do not compensate for the core system's special-case * adjustment of location to that of the leading '-' * operator in the event of a negative constant. It is * also useful for our purposes to start from the minus * symbol. In this way, queries like "select * from foo * where bar = 1" and "select * from foo where bar = -2" * will have identical normalized query strings. */ tok = core_yylex(&yylval, &yylloc, yyscanner); if (tok == 0) break; /* out of inner for-loop */ } /* * We now rely on the assumption that flex has placed a zero * byte after the text of the current token in scanbuf. */ locs[i].length = strlen(yyextra.scanbuf + loc); break; /* out of inner for-loop */ } } /* If we hit end-of-string, give up, leaving remaining lengths -1 */ if (tok == 0) break; last_loc = loc; } scanner_finish(yyscanner); } /* * comp_location: comparator for qsorting LocationLen structs by location */ static int comp_location(const void *a, const void *b) { int l = ((const LocationLen *) a)->location; int r = ((const LocationLen *) b)->location; if (l < r) return -1; else if (l > r) return +1; else return 0; }