Re: [PATCHES] On-disk bitmap index implementation
Gavin Sherry wrote: There are still some things Jie and I have not gotten to yet: ... o Test WAL replay more thoroughly. Found one WAL related bug: postgres=# CREATE TABLE test (i int); CREATE TABLE postgres=# INSERT INTO test SELECT a FROM generate_series(1,10) a; INSERT 0 10 postgres=# CREATE INDEX mdx ON test USING bitmap(i); CREATE INDEX postgres=# INSERT INTO test VALUES (11); INSERT 0 1 postgres=# \q killall -9 postgres, and restart. Redo fails with: PANIC: bm_insert_redo: LOV item is not inserted in pos 2(requested 12) CONTEXT: xlog redo insert a new LOV item: rel 1663/10817/16388 I haven't dug deeper yet. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PATCHES] On-disk bitmap index implementation
On Wed, 27 Dec 2006, Heikki Linnakangas wrote: Gavin Sherry wrote: There are still some things Jie and I have not gotten to yet: ... o Test WAL replay more thoroughly. Found one WAL related bug: postgres=# CREATE TABLE test (i int); CREATE TABLE postgres=# INSERT INTO test SELECT a FROM generate_series(1,10) a; INSERT 0 10 postgres=# CREATE INDEX mdx ON test USING bitmap(i); CREATE INDEX postgres=# INSERT INTO test VALUES (11); INSERT 0 1 postgres=# \q killall -9 postgres, and restart. Redo fails with: PANIC: bm_insert_redo: LOV item is not inserted in pos 2(requested 12) CONTEXT: xlog redo insert a new LOV item: rel 1663/10817/16388 I haven't dug deeper yet. Yes, there were a bunch of WAL issues we wanted to address. Jie has been working on this too. Thanks for the feedback, we can use this as a test. Thanks, Gavin ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [PATCHES] On-disk bitmap index implementation
Gavin Sherry wrote: o Improving VACUUM support -- currently, VACUUM FULL means REINDEX for bitmaps. Heikki Linnakangas offered to work on this. Heikki, are you still interested? BTW vacuuming seems quite broken as it is: [EMAIL PROTECTED]:~/pgsql.bitmap$ ~/pgsql.bitmap/bin/psql -a postgres vacuumtest.sql drop table if exists test; DROP TABLE create table test (key int); CREATE TABLE create index test_bm on test using bitmap (key); CREATE INDEX insert into test values (1); INSERT 0 1 delete from test; DELETE 1 vacuum test; VACUUM insert into test values (2); INSERT 0 1 select * from test where key = 1; key - 2 (1 row) -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PATCHES] On-disk bitmap index implementation
On Tue, 5 Dec 2006, Heikki Linnakangas wrote: Gavin Sherry wrote: o Improving VACUUM support -- currently, VACUUM FULL means REINDEX for bitmaps. Heikki Linnakangas offered to work on this. Heikki, are you still interested? BTW vacuuming seems quite broken as it is: [EMAIL PROTECTED]:~/pgsql.bitmap$ ~/pgsql.bitmap/bin/psql -a postgres vacuumtest.sql drop table if exists test; DROP TABLE create table test (key int); CREATE TABLE create index test_bm on test using bitmap (key); CREATE INDEX insert into test values (1); INSERT 0 1 delete from test; DELETE 1 vacuum test; VACUUM insert into test values (2); INSERT 0 1 select * from test where key = 1; key - 2 (1 row) Oops :-). Thanks for pointing it out. I think I might have busted something merging with HEAD. Don't you hate that? Thanks, Gavin ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [PATCHES] On-disk bitmap index implementation
On Tue, 2006-12-05 at 00:18 +1100, Gavin Sherry wrote: o Determine if we need to provide anything for rm_startup, rm_cleanup, rm_safe_restartpoint RmgrData function pointers. safe_restartpoint gives true/false based upon whether there are multi-record WAL states that have only been partially received. For example, a btree index split needs multiple WAL records as it recurses up the index tree. If you've got one record but not the others yet you have an incomplete state and so cannot safely write a restartpoint. I'll document that if you/anyone might suggest where the best place is? o Look into adding an AM option such that the user can determine word size at index creation time. For higher-cardinality data (above 1000 distinct values), 16 bit word sizes can really help with performance. Although the word size is not just assumed to be a certain size across the code, macros are used extensively to interact with the word size. Making it different for each index might be a little messy. ...and is is it a typical case to have a bitmap with less than 1000 distinct values?? Surely we want that as the sole assumption? Nearly unique bitmaps can suffer a little I think, if it makes the most common case faster. But I'd like to see the perf results first, I guess. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PATCHES] On-disk bitmap index implementation
Gavin Sherry wrote: Hi all, Attached is a patch implementing bitmap indexes. It includes major enhancements on the patch submitted during feature freeze for 8.2 here[1]. In particular: much better integration with the existing bitmap scan code with the internals of the bitmap streaming pushed down into the AM and hidden from the executor code; completely new index creation algorithm which reduced creation time by 20-75% depending on the data; modifications to the encoding mechanism to suit the integration with bitmap index scans; work on memory management; lots of code rewriting; range query support. The code is also much cleaner now. Thanks! I'll take a look at it. We need to give the indexam API some further thought. As you know, I've been working on the Grouped Index Tuples stuff, which also requires changes to the API to get full benefit. There's a bunch of functionality I'd like to see: * Support for streamed bitmaps, like you have implemented. * Support for candidate matches. This is needed for GIT, as well as range-encoded bitmap indexes if/when we add them. * Support for returning tuples in partial order. This is again needed for GIT, because grouped tuples don't keep track of the ordering within the group, so they need to be sorted if ordering necessary. And again it's also useful to return tuples in order from range-encoded bitmaps. * Support for kill_prior_tuple on bitmap scans. * A bulk insert API. When inserting a lot of tuples with similar keys, we could a considerable amount of CPU with a bulk insert API. A bulk insert to a B-tree for example would only need to descend the tree once, find the insert location, lock the target page just once and insert all the tuples that belong to that page. That would potentially also reduce WAL traffic. There are still some things Jie and I have not gotten to yet: o Improving VACUUM support -- currently, VACUUM FULL means REINDEX for bitmaps. Heikki Linnakangas offered to work on this. Heikki, are you still interested? Yeah, I can look into that. o Test WAL replay more thoroughly. I've had that problem too with a lot of things I've hacked. I've used a shell script that does the operation under test, runs a select, kills and restarts postmaster, and reruns the select. If the select after crash returns the same result as before, presumably WAL code works. But you need to watch out for full page writes that might mask bugs in the redo code. Anyone have a more sophisticated method? -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PATCHES] On-disk bitmap index implementation
Heikki Linnakangas wrote: We need to give the indexam API some further thought. As you know, I've been working on the Grouped Index Tuples stuff, which also requires changes to the API to get full benefit. There's a bunch of functionality I'd like to see: * Support for streamed bitmaps, like you have implemented. * Support for candidate matches. This is needed for GIT, as well as range-encoded bitmap indexes if/when we add them. * Support for returning tuples in partial order. This is again needed for GIT, because grouped tuples don't keep track of the ordering within the group, so they need to be sorted if ordering necessary. And again it's also useful to return tuples in order from range-encoded bitmaps. * Support for kill_prior_tuple on bitmap scans. * A bulk insert API. When inserting a lot of tuples with similar keys, we could a considerable amount of CPU with a bulk insert API. A bulk insert to a B-tree for example would only need to descend the tree once, find the insert location, lock the target page just once and insert all the tuples that belong to that page. That would potentially also reduce WAL traffic. Forgot one: * Ability return index tuple contents, not just pointers to heap, to allow the executor to use the values stored in the index, see http://archives.postgresql.org/pgsql-performance/2006-09/msg00080.php -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [PATCHES] On-disk bitmap index implementation
On Mon, 4 Dec 2006, Simon Riggs wrote: On Tue, 2006-12-05 at 00:18 +1100, Gavin Sherry wrote: o Determine if we need to provide anything for rm_startup, rm_cleanup, rm_safe_restartpoint RmgrData function pointers. safe_restartpoint gives true/false based upon whether there are multi-record WAL states that have only been partially received. For example, a btree index split needs multiple WAL records as it recurses up the index tree. If you've got one record but not the others yet you have an incomplete state and so cannot safely write a restartpoint. I'll document that if you/anyone might suggest where the best place is? transam/README ? o Look into adding an AM option such that the user can determine word size at index creation time. For higher-cardinality data (above 1000 distinct values), 16 bit word sizes can really help with performance. Although the word size is not just assumed to be a certain size across the code, macros are used extensively to interact with the word size. Making it different for each index might be a little messy. ...and is is it a typical case to have a bitmap with less than 1000 distinct values?? Surely we want that as the sole assumption? Nearly unique bitmaps can suffer a little I think, if it makes the most common case faster. But I'd like to see the perf results first, I guess. I'll put together some performance data on different word sizes. Thanks, Gavin ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PATCHES] On-disk bitmap index implementation
On Mon, 4 Dec 2006, Heikki Linnakangas wrote: o Test WAL replay more thoroughly. I've had that problem too with a lot of things I've hacked. I've used a shell script that does the operation under test, runs a select, kills and restarts postmaster, and reruns the select. If the select after crash returns the same result as before, presumably WAL code works. But you need to watch out for full page writes that might mask bugs in the redo code. Anyone have a more sophisticated method? Well, I've done a combination of what you did and replaying a bunch of operations using PITR. Thanks, Gavin ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
