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Show ignored constants as "$N" rather than "?" in pg_stat_statements.

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The trouble with the original choice here is that "?" is a valid (and
indeed used) operator name, so that you could end up with ambiguous
statement texts like "SELECT ? ? ?".  With this patch, you instead
see "SELECT $1 ? $2", which seems significantly more readable.
The numbers used for this purpose begin after the last actual $N parameter
in the particular query.  The conflict with external parameters has its own
potential for confusion of course, but it was agreed to be an improvement
over the previous behavior.

Lukas Fittl

Discussion: https://postgr.es/m/CAP53PkxeaCuwYmF-A4J5z2-qk5fYFo5_NH3gpXGJJBxv1DMwEw@mail.gmail.com
This commit is contained in:
Tom Lane
2017-03-27 20:14:36 -04:00
parent 6462238f0d
commit a6f22e8356
4 changed files with 142 additions and 56 deletions
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40
contrib/pg_stat_statements/pg_stat_statements.c
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@ -27,10 +27,10 @@
* to blame query costs on the proper queryId.
*
* To facilitate presenting entries to users, we create "representative" query
* strings in which constants are replaced with '?' characters, to make it
* clearer what a normalized entry can represent. To save on shared memory,
* and to avoid having to truncate oversized query strings, we store these
* strings in a temporary external query-texts file. Offsets into this
* strings in which constants are replaced with parameter symbols ($n), to
* make it clearer what a normalized entry can represent. To save on shared
* memory, and to avoid having to truncate oversized query strings, we store
* these strings in a temporary external query-texts file. Offsets into this
* file are kept in shared memory.
*
* Note about locking issues: to create or delete an entry in the shared
@ -219,6 +219,9 @@ typedef struct pgssJumbleState
/* Current number of valid entries in clocations array */
int clocations_count;
/* highest Param id we've seen, in order to start normalization correctly */
int highest_extern_param_id;
} pgssJumbleState;
/*---- Local variables ----*/
@ -803,6 +806,7 @@ pgss_post_parse_analyze(ParseState *pstate, Query *query)
jstate.clocations = (pgssLocationLen *)
palloc(jstate.clocations_buf_size * sizeof(pgssLocationLen));
jstate.clocations_count = 0;
jstate.highest_extern_param_id = 0;
/* Compute query ID and mark the Query node with it */
JumbleQuery(&jstate, query);
@ -2482,6 +2486,10 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
APP_JUMB(p->paramkind);
APP_JUMB(p->paramid);
APP_JUMB(p->paramtype);
/* Also, track the highest external Param id */
if (p->paramkind == PARAM_EXTERN &&
p->paramid > jstate->highest_extern_param_id)
jstate->highest_extern_param_id = p->paramid;
}
break;
case T_Aggref:
@ -2874,7 +2882,7 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
break;
case T_TableFunc:
{
TableFunc *tablefunc = (TableFunc *) node;
TableFunc *tablefunc = (TableFunc *) node;
JumbleExpr(jstate, tablefunc->docexpr);
JumbleExpr(jstate, tablefunc->rowexpr);
@ -2938,7 +2946,8 @@ RecordConstLocation(pgssJumbleState *jstate, int location)
* of interest, so it's worth doing.)
*
* *query_len_p contains the input string length, and is updated with
* the result string length (which cannot be longer) on exit.
* 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.
*/
@ -2949,6 +2958,7 @@ generate_normalized_query(pgssJumbleState *jstate, const char *query,
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 */
@ -2961,8 +2971,17 @@ generate_normalized_query(pgssJumbleState *jstate, const char *query,
*/
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 $n symbol
* certainly isn't more than 11 bytes, even if n reaches INT_MAX. We
* could refine that limit based on the max value of n for the current
* query, but it hardly seems worth any extra effort to do so.
*/
norm_query_buflen = query_len + jstate->clocations_count * 10;
/* Allocate result buffer */
norm_query = palloc(query_len + 1);
norm_query = palloc(norm_query_buflen + 1);
for (i = 0; i < jstate->clocations_count; i++)
{
@ -2986,8 +3005,9 @@ generate_normalized_query(pgssJumbleState *jstate, const char *query,
memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
n_quer_loc += len_to_wrt;
/* And insert a '?' in place of the constant token */
norm_query[n_quer_loc++] = '?';
/* And insert a param symbol in place of the constant token */
n_quer_loc += sprintf(norm_query + n_quer_loc, "$%d",
i + 1 + jstate->highest_extern_param_id);
quer_loc = off + tok_len;
last_off = off;
@ -3004,7 +3024,7 @@ generate_normalized_query(pgssJumbleState *jstate, const char *query,
memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
n_quer_loc += len_to_wrt;
Assert(n_quer_loc <= query_len);
Assert(n_quer_loc <= norm_query_buflen);
norm_query[n_quer_loc] = '\0';
*query_len_p = n_quer_loc;