WT-10807 Skip in-memory deleted pages as part of the tree walk (6.0 backport) #10588
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Traversing an in-memory page that contains all the deleted values that are visible to the current transaction, leading to an increase in latency due to the time spent skipping these deleted values. By saving the aggregated timestamp information in the ref when the page has all deleted values, this aggregated information can be validated against the transaction snapshot to skip traversing the page completely and improve the latency when there are many deleted pages. The downside of this approach is that the in-memory size of each ref is increased by 8 more bytes, but this increase shouldn't cause any problem. (cherry picked from commit d121cca) (cherry picked from commit eed05eb)
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| * could potentially skip pages. The skip function looks at the aggregated timestamp | ||
| * information to determine if something is visible on the page. If nothing is, the page is | ||
| * skipped. | ||
| * If we are running with snapshot isolation, have a snapshot, and are not interested in |
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Looks like this comment was missed on 7.0
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It is the only change required in 6.0 due to the checkpoint cursors that are not supported, but there exists so many tests that test checkpoint cursors.
| */ | ||
| if (!F_ISSET(&cbt->iface, WT_CURSTD_KEY_ONLY) && | ||
| session->txn->isolation == WT_ISO_SNAPSHOT && | ||
| F_ISSET(session->txn, WT_TXN_HAS_SNAPSHOT) && |
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Looks like this was missed on 7.0
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It is the only change required in 6.0 due to the checkpoint cursors that are not supported, but there exists so many tests that test checkpoint cursors.
| __wt_ref_addr_copy(session, ref, &addr) && addr.ta.newest_stop_txn != WT_TXN_MAX && | ||
| addr.ta.newest_stop_ts != WT_TS_MAX && | ||
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| if (previous_state == WT_REF_MEM && !__wt_page_is_modified(ref->page)) |
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There was this more in 7.0 when the ref is deleted:
walk_skip_stats->total_del_pages_skipped++;
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Yes, those code changes are due to the fast truncate data format changes. As those conditions are not possible in 6.0, we do not need it.
Traversing an in-memory page that contains all the deleted values that are visible to the current transaction, leading to an increase in latency due
to the time spent skipping these deleted values.
By saving the aggregated timestamp information in the ref when the page has all deleted values, this aggregated information can be validated against the transaction snapshot to skip traversing the page completely and improve the latency when there are many deleted pages.
The downside of this approach is that the in-memory size of each ref is increased by 8 more bytes, but this increase shouldn't cause any problem.
(cherry picked from commit d121cca) (cherry picked from commit eed05eb)