diff options
Diffstat (limited to 'src/include')
| -rw-r--r-- | src/include/utils/snapmgr.h | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h index 6a80f0ba550..42706966f10 100644 --- a/src/include/utils/snapmgr.h +++ b/src/include/utils/snapmgr.h @@ -19,6 +19,19 @@ #include "utils/snapshot.h" +/* + * The structure used to map times to TransactionId values for the "snapshot + * too old" feature must have a few entries at the tail to hold old values; + * otherwise the lookup will often fail and the expected early pruning or + * vacuum will not usually occur. It is best if this padding is for a number + * of minutes greater than a thread would normally be stalled, but it's OK if + * early vacuum opportunities are occasionally missed, so there's no need to + * use an extreme value or get too fancy. 10 minutes seems plenty. + */ +#define OLD_SNAPSHOT_PADDING_ENTRIES 10 +#define OLD_SNAPSHOT_TIME_MAP_ENTRIES (old_snapshot_threshold + OLD_SNAPSHOT_PADDING_ENTRIES) + + /* GUC variables */ extern PGDLLIMPORT int old_snapshot_threshold; |