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PG-254: Add query location to hash table entries.

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Whenever a new query is added to a query buffer, record the position
in which the query was inserted, we can then use this information to
locate the query in a faster way later on when required.

This allowed to simplify the logic in hash_entry_dealloc(), after
creating the list of pending queries, as the list is scanned we can copy
the query from the previous query buffer to the new one by using the
query position (query_pos), this avoids scanning the whole query buffer
when looking up for the queryid.

Also, when moving a query to a new buffer (copy_query), we update
the query_pos for the hash table entry, so it points to the right place
in the new query buffer.

read_query() function was updated to allow query position to be passed
as argument, if pos != 0 use it to locate the query directly, otherwise
fallback to the previous mode of scanning the whole buffer.

SaveQueryText() was updated to pass a reference to the query position as
argument, this value is updated after the function finishes with the
position that the query was stored into the buffer.
This commit is contained in:
Diego Fronza
2021-10-07 10:06:20 -03:00
parent fcb70ffed1
commit 8fdf0946fe
3 changed files with 98 additions and 144 deletions
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62
pg_stat_monitor.c
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@@ -1501,6 +1501,8 @@ pgss_store(uint64 queryid,
if (!entry)
{
uint64 prev_qbuf_len;
/* position in which the query's text was inserted into the query buffer. */
size_t qpos = 0;
query_len = strlen(query);
if (query_len > PGSM_QUERY_MAX_LEN)
@@ -1516,7 +1518,7 @@ pgss_store(uint64 queryid,
* original length.
*/
memcpy(&prev_qbuf_len, pgss_qbuf[bucketid], sizeof(prev_qbuf_len));
if (!SaveQueryText(bucketid, queryid, pgss_qbuf[bucketid], query, query_len))
if (!SaveQueryText(bucketid, queryid, pgss_qbuf[bucketid], query, query_len, &qpos))
{
LWLockRelease(pgss->lock);
elog(DEBUG1, "pg_stat_monitor: insufficient shared space for query.");
@@ -1533,6 +1535,7 @@ pgss_store(uint64 queryid,
elog(DEBUG1, "pg_stat_monitor: out of memory");
return;
}
entry->query_pos = qpos;
}
if (jstate == NULL)
@@ -1689,7 +1692,7 @@ pg_stat_monitor_internal(FunctionCallInfo fcinfo,
bool is_allowed_role = is_member_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS);
#endif
if (read_query(buf, bucketid, queryid, query_txt) == 0)
if (read_query(buf, queryid, query_txt, entry->query_pos) == 0)
{
int len;
len = read_query_buffer(bucketid, queryid, query_txt);
@@ -1709,16 +1712,16 @@ pg_stat_monitor_internal(FunctionCallInfo fcinfo,
if (tmp.state == PGSS_FINISHED)
continue;
}
if (tmp.info.parentid != UINT64CONST(0))
{
int len = 0;
if (read_query(buf, bucketid, tmp.info.parentid, parent_query_txt) == 0)
{
len = read_query_buffer(bucketid, tmp.info.parentid, parent_query_txt);
if (len != MAX_QUERY_BUFFER_BUCKET)
snprintf(parent_query_txt, 32, "%s", "<insufficient disk/shared space>");
}
}
if (tmp.info.parentid != UINT64CONST(0))
{
int len = 0;
if (read_query(buf, tmp.info.parentid, parent_query_txt, 0) == 0)
{
len = read_query_buffer(bucketid, tmp.info.parentid, parent_query_txt);
if (len != MAX_QUERY_BUFFER_BUCKET)
snprintf(parent_query_txt, 32, "%s", "<insufficient disk/shared space>");
}
}
/* bucketid at column number 0 */
values[i++] = Int64GetDatumFast(bucketid);
@@ -2984,7 +2987,7 @@ intarray_get_datum(int32 arr[], int len)
}
uint64
read_query(unsigned char *buf, uint64 bucketid, uint64 queryid, char * query)
read_query(unsigned char *buf, uint64 queryid, char * query, size_t pos)
{
bool found = false;
uint64 query_id = 0;
@@ -2996,6 +2999,27 @@ read_query(unsigned char *buf, uint64 bucketid, uint64 queryid, char * query)
if (buf_len <= 0)
goto exit;
/* If a position hint is given, try to locate the query directly. */
if (pos != 0 && (pos + sizeof(uint64) + sizeof(uint64)) < buf_len)
{
memcpy(&query_id, &buf[pos], sizeof(uint64));
if (query_id != queryid)
return 0;
pos += sizeof(uint64);
memcpy(&query_len, &buf[pos], sizeof(uint64)); /* query len */
pos += sizeof(uint64);
if (pos + query_len > buf_len) /* avoid reading past buffer's length. */
return 0;
memcpy(query, &buf[pos], query_len); /* Actual query */
query[query_len] = '\0';
return queryid;
}
rlen = sizeof (uint64); /* Move forwad to skip length bytes */
for(;;)
{
@@ -3005,6 +3029,7 @@ read_query(unsigned char *buf, uint64 bucketid, uint64 queryid, char * query)
memcpy(&query_id, &buf[rlen], sizeof (uint64)); /* query id */
if (query_id == queryid)
found = true;
rlen += sizeof (uint64);
if (buf_len <= rlen)
continue;
@@ -3034,7 +3059,12 @@ exit:
}
bool
SaveQueryText(uint64 bucketid, uint64 queryid, unsigned char *buf, const char *query, uint64 query_len)
SaveQueryText(uint64 bucketid,
uint64 queryid,
unsigned char *buf,
const char *query,
uint64 query_len,
size_t *query_pos)
{
uint64 buf_len = 0;
@@ -3059,6 +3089,8 @@ SaveQueryText(uint64 bucketid, uint64 queryid, unsigned char *buf, const char *q
}
}
*query_pos = buf_len;
memcpy(&buf[buf_len], &queryid, sizeof (uint64)); /* query id */
buf_len += sizeof (uint64);
@@ -3293,7 +3325,7 @@ read_query_buffer(int bucket_id, uint64 queryid, char *query_txt)
break;
}
off += buf_len;
if (read_query(buf, bucket_id, queryid, query_txt))
if (read_query(buf, queryid, query_txt, 0))
break;
}
if (fd > 0)