diff options
Diffstat (limited to 'src/include/pgstat.h')
| -rw-r--r-- | src/include/pgstat.h | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/src/include/pgstat.h b/src/include/pgstat.h index 4be09fe8dc3..a078b61060e 100644 --- a/src/include/pgstat.h +++ b/src/include/pgstat.h @@ -219,7 +219,20 @@ typedef struct PgStat_MsgDummy /* ---------- * PgStat_MsgInquiry Sent by a backend to ask the collector - * to write the stats file. + * to write the stats file(s). + * + * Ordinarily, an inquiry message prompts writing of the global stats file, + * the stats file for shared catalogs, and the stats file for the specified + * database. If databaseid is InvalidOid, only the first two are written. + * + * New file(s) will be written only if the existing file has a timestamp + * older than the specified cutoff_time; this prevents duplicated effort + * when multiple requests arrive at nearly the same time, assuming that + * backends send requests with cutoff_times a little bit in the past. + * + * clock_time should be the requestor's current local time; the collector + * uses this to check for the system clock going backward, but it has no + * effect unless that occurs. We assume clock_time >= cutoff_time, though. * ---------- */ @@ -228,7 +241,7 @@ typedef struct PgStat_MsgInquiry PgStat_MsgHdr m_hdr; TimestampTz clock_time; /* observed local clock time */ TimestampTz cutoff_time; /* minimum acceptable file timestamp */ - Oid databaseid; /* requested DB (InvalidOid => all DBs) */ + Oid databaseid; /* requested DB (InvalidOid => shared only) */ } PgStat_MsgInquiry; |