Hello Todd Lipcon,
I'd like you to do a code review. Please visit
http://gerrit.cloudera.org:8080/10328
to review the following change.
Change subject: Fast path scanning blocks of deleted rows
......................................................................
Fast path scanning blocks of deleted rows
This adds some very simple fast-paths in the case that an entire row
block consists of rows that were deleted.
The first is in the block materialization code: if delta application
results in all rows being deleted, we don't need to move forward and
materialize any columns.
The second is before serializing scan responses to the client. In this
case we don't need to loop over each column and read the selection
vector for each column. Instead we can just return immediately.
I tested this on a table where I'd inserted a few billion rows, deleted
them all, and then re-inserted them. Before the patch, a simple 'SELECT
* FROM t LIMIT 10' took 306sec. With the first optimization only, it
took about 10 seconds. With the second one as well, it took about 2.2
seconds.
There are probably more general optimizations that could be done for
sparsely-populated RowBlocks (eg where just a few rows are selected) but
they are much more complex, and it's relatively common for users to
delete large consecutive runs of rows. For example, users may use
'DELETE' all rows in a table or partition before re-adding them, or they
may delete all data corresponding to some prefix of the PK.
Change-Id: I9fa891c0f4e857ddd1f873ad4855154d078be6b8
Reviewed-on: http://gerrit.cloudera.org:8080/10213
Tested-by: Todd Lipcon <[email protected]>
Reviewed-by: Will Berkeley <[email protected]>
---
M src/kudu/common/generic_iterators.cc
M src/kudu/tserver/tablet_service.cc
2 files changed, 13 insertions(+), 2 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/28/10328/1
--
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Gerrit-Project: kudu
Gerrit-Branch: branch-1.7.x
Gerrit-MessageType: newchange
Gerrit-Change-Id: I9fa891c0f4e857ddd1f873ad4855154d078be6b8
Gerrit-Change-Number: 10328
Gerrit-PatchSet: 1
Gerrit-Owner: Will Berkeley <[email protected]>
Gerrit-Reviewer: Todd Lipcon <[email protected]>
