diff options
Diffstat (limited to 'src/include/storage/proc.h')
| -rw-r--r-- | src/include/storage/proc.h | 37 |
1 files changed, 36 insertions, 1 deletions
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index a58888f9e90..36ecf7d0058 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -86,6 +86,41 @@ struct XidCache */ #define INVALID_PGPROCNO PG_INT32_MAX +/* + * Flags for PGPROC.delayChkpt + * + * These flags can be used to delay the start or completion of a checkpoint + * for short periods. A flag is in effect if the corresponding bit is set in + * the PGPROC of any backend. + * + * For our purposes here, a checkpoint has three phases: (1) determine the + * location to which the redo pointer will be moved, (2) write all the + * data durably to disk, and (3) WAL-log the checkpoint. + * + * Setting DELAY_CHKPT_START prevents the system from moving from phase 1 + * to phase 2. This is useful when we are performing a WAL-logged modification + * of data that will be flushed to disk in phase 2. By setting this flag + * before writing WAL and clearing it after we've both written WAL and + * performed the corresponding modification, we ensure that if the WAL record + * is inserted prior to the new redo point, the corresponding data changes will + * also be flushed to disk before the checkpoint can complete. (In the + * extremely common case where the data being modified is in shared buffers + * and we acquire an exclusive content lock on the relevant buffers before + * writing WAL, this mechanism is not needed, because phase 2 will block + * until we release the content lock and then flush the modified data to + * disk.) + * + * Setting DELAY_CHKPT_COMPLETE prevents the system from moving from phase 2 + * to phase 3. This is useful if we are performing a WAL-logged operation that + * might invalidate buffers, such as relation truncation. In this case, we need + * to ensure that any buffers which were invalidated and thus not flushed by + * the checkpoint are actaully destroyed on disk. Replay can cope with a file + * or block that doesn't exist, but not with a block that has the wrong + * contents. + */ +#define DELAY_CHKPT_START (1<<0) +#define DELAY_CHKPT_COMPLETE (1<<1) + typedef enum { PROC_WAIT_STATUS_OK, @@ -191,7 +226,7 @@ struct PGPROC pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition * started */ - bool delayChkpt; /* true if this proc delays checkpoint start */ + int delayChkpt; /* for DELAY_CHKPT_* flags */ uint8 statusFlags; /* this backend's status flags, see PROC_* * above. mirrored in |