Re: Batch insert in CTAS/MatView code
On Wed, May 26, 2021 at 12:49 PM tsunakawa.ta...@fujitsu.com wrote: > > From: Bharath Rupireddy > > I think the "New Table Access Methods for Multi and Single Inserts" > > patches at [1] make multi insert usage easy for COPY, CTAS/Create Mat > > View, Refresh Mat View and so on. It also has a patch for multi > > inserts in CTAS and Refresh Mat View > > (v6-0002-CTAS-and-REFRESH-Mat-View-With-New-Multi-Insert-T.patch). > > Please see that thread and feel free to review it. > > Ouch, I didn't notice that the patch was reborn in that thread. OK. > > Could you add it to the CF if you haven't yet? It already has one - https://commitfest.postgresql.org/33/2871/ With Regards, Bharath Rupireddy. EnterpriseDB: http://www.enterprisedb.com
RE: Batch insert in CTAS/MatView code
From: Bharath Rupireddy > I think the "New Table Access Methods for Multi and Single Inserts" > patches at [1] make multi insert usage easy for COPY, CTAS/Create Mat > View, Refresh Mat View and so on. It also has a patch for multi > inserts in CTAS and Refresh Mat View > (v6-0002-CTAS-and-REFRESH-Mat-View-With-New-Multi-Insert-T.patch). > Please see that thread and feel free to review it. Ouch, I didn't notice that the patch was reborn in that thread. OK. Could you add it to the CF if you haven't yet? Regards Takayuki Tsunakawa
Re: Batch insert in CTAS/MatView code
On Wed, May 26, 2021 at 12:18 PM tsunakawa.ta...@fujitsu.com wrote: > > Hello Paul-san, > > From: Daniel Gustafsson > > In an off-list discussion with Paul, we decided to withdraw this patch for > > now > > and instead create a new entry when there is a re-worked patch. This has > > now > > been done in the CF app. > > Would you mind if I take over this patch for PG 15? I find this promising, > as Bharath-san demonstrated good performance by combining your patch and the > parallel CTAS that Bharath-san has been working on. We'd like to do things > that enhance parallelism. > > Please allow me to start posting the revised patches next week if I can't get > your reply. Hi, I think the "New Table Access Methods for Multi and Single Inserts" patches at [1] make multi insert usage easy for COPY, CTAS/Create Mat View, Refresh Mat View and so on. It also has a patch for multi inserts in CTAS and Refresh Mat View (v6-0002-CTAS-and-REFRESH-Mat-View-With-New-Multi-Insert-T.patch). Please see that thread and feel free to review it. [1] - https://www.postgresql.org/message-id/CALj2ACXdrOmB6Na9amHWZHKvRT3Z0nwTRsCwoMT-npOBtmXLXg%40mail.gmail.com With Regards, Bharath Rupireddy. EnterpriseDB: http://www.enterprisedb.com
RE: Batch insert in CTAS/MatView code
Hello Paul-san, From: Daniel Gustafsson > In an off-list discussion with Paul, we decided to withdraw this patch for now > and instead create a new entry when there is a re-worked patch. This has > now > been done in the CF app. Would you mind if I take over this patch for PG 15? I find this promising, as Bharath-san demonstrated good performance by combining your patch and the parallel CTAS that Bharath-san has been working on. We'd like to do things that enhance parallelism. Please allow me to start posting the revised patches next week if I can't get your reply. Regards Takayuki Tsunakawa
Re: Batch insert in CTAS/MatView code
In an off-list discussion with Paul, we decided to withdraw this patch for now and instead create a new entry when there is a re-worked patch. This has now been done in the CF app. cheers ./daniel
Re: Batch insert in CTAS/MatView code
I took some time on digging the issue yesterday so the main concern of the
patch is to get the tuple length from ExecFetchSlotHeapTuple().
+ ExecCopySlot(batchslot, slot);
+ tuple = ExecFetchSlotHeapTuple(batchslot, true, NULL);
+
+ myState->mi_slots_num++;
+ myState->mi_slots_size += tuple->t_len;
We definitely should remove ExecFetchSlotHeapTuple() here but we need to
know the tuple length (at least rough length). One solution might be using
memory context stat info as mentioned, the code looks like this.
tup_len = MemoryContextUsedSize(batchslot->tts_mcxt);
ExecCopySlot(batchslot, slot);
ExecMaterializeSlot(batchslot);
tup_len = MemoryContextUsedSize(batchslot->tts_mcxt) - tup_len;
MemoryContextUsedSize() is added to calculate the total used size (simply
hack to use the stats interface).
+int
+MemoryContextUsedSize(MemoryContext context)
+{
+ MemoryContextCounters total;
+
+ memset(, 0, sizeof(total));
+ context->methods->stats(context, NULL, NULL, );
+
+ return total.totalspace - total.freespace;
+}
This basically works but there are concerns:
The length is not accurate (though we do not need to be that accurate)
since there are
some additional memory allocations, but we are not sure if the size is
not much
larger than the real length for some slot types in the future and I'm
not sure whether we
definitely allocate at least the tuple length in the memory context
after materialization
for all slot types in the future. Last is that the code seems to be a
bit ugly also.
As a reference, For "create table t1 as select * from t2", the above
code returns
"tuple length" is 88 (real tuple length is 4).
Another solution is that maybe return the real size
in ExecMaterializeSlot()? e.g.
ExecMaterializeSlot(slot, _len); For this we probably want to store the
length
in the slot struct for performance.
For the COPY case the tuple length is known in advance but I can image more
cases
which do not know the size but need that for the multi_insert interface, at
least I'm
wondering if we should use that in 'refresh matview' and fast path for
Insert node
(I heard some complaints about the performance of "insert into tbl from
select..."
from some of our users)? So the concern is not just for the case in this
patch.
Besides, My colleagues Ashwin Agrawal and Adam Lee found maybe could
try raw_heap_insert() similar code for ctas and compare since it is do
insert in
a new created table. That would involve more discussions, much more code
change and need to test more (stability and performance). So multi insert
seems
to be a stable solution in a short time given that has been used in COPY
for a
long time?
Whatever the solution for CTAS we need to address the concern of tuple size
for multi insert cases.
Re: Batch insert in CTAS/MatView code
On Mon, Sep 30, 2019 at 12:38:02AM -0700, Andres Freund wrote: > That does not strike me as a good idea. The upper layer is going to need > to manage some resources (e.g. it's the only bit that knows about how to > manage lifetime of the incoming data), and by exposing it to each AM > we're going to duplicate the necessary code too. Latest status of the thread maps with a patch which still applies, still the discussion could go on as more review is needed. So I have moved it to next CF. -- Michael signature.asc Description: PGP signature
Re: Batch insert in CTAS/MatView code
Hi, On 2019-09-30 12:12:31 +0800, Paul Guo wrote: > > > > However, I can also see that there is no better alternative. We need > > to > > > > compute the size of accumulated tuples so far, in order to decide > > whether > > > > to stop accumulating tuples. There is no convenient way to obtain the > > > > length of the tuple, given a slot. How about making that decision > > solely > > > > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple > > call > > > > altogether? > > > > > > ... maybe we should add a new operation to slots, that returns the > > > (approximate?) size of a tuple? > > > > Hm, I'm not convinced that it's worth adding that as a dedicated > > operation. It's not that clear what it'd exactly mean anyway - what > > would it measure? As referenced in the slot? As if it were stored on > > disk? etc? > > > > I wonder if the right answer wouldn't be to just measure the size of a > > memory context containing the batch slots, or something like that. > > > > > Probably a better way is to move those logic (append slot to slots, judge > when to flush, flush, clean up slots) into table_multi_insert()? That does not strike me as a good idea. The upper layer is going to need to manage some resources (e.g. it's the only bit that knows about how to manage lifetime of the incoming data), and by exposing it to each AM we're going to duplicate the necessary code too. > Generally the final implementation of table_multi_insert() should be > able to know the sizes easily. One concern is that currently just COPY > in the repo uses multi insert, so not sure if other callers in the > future want their own logic (or set up a flag to allow customization > but seems a bit over-designed?). And that is also a concern, it seems unlikely that we'll get the interface good. Greetings, Andres Freund
Re: Batch insert in CTAS/MatView code
> > > > > However, I can also see that there is no better alternative. We need > to > > > compute the size of accumulated tuples so far, in order to decide > whether > > > to stop accumulating tuples. There is no convenient way to obtain the > > > length of the tuple, given a slot. How about making that decision > solely > > > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple > call > > > altogether? > > > > ... maybe we should add a new operation to slots, that returns the > > (approximate?) size of a tuple? > > Hm, I'm not convinced that it's worth adding that as a dedicated > operation. It's not that clear what it'd exactly mean anyway - what > would it measure? As referenced in the slot? As if it were stored on > disk? etc? > > I wonder if the right answer wouldn't be to just measure the size of a > memory context containing the batch slots, or something like that. > > Probably a better way is to move those logic (append slot to slots, judge when to flush, flush, clean up slots) into table_multi_insert()? Generally the final implementation of table_multi_insert() should be able to know the sizes easily. One concern is that currently just COPY in the repo uses multi insert, so not sure if other callers in the future want their own logic (or set up a flag to allow customization but seems a bit over-designed?).
Re: Batch insert in CTAS/MatView code
On Sat, Sep 28, 2019 at 5:49 AM Andres Freund wrote:
> Hi,
>
> On 2019-09-09 18:31:54 +0800, Paul Guo wrote:
> > diff --git a/src/backend/access/heap/heapam.c
> b/src/backend/access/heap/heapam.c
> > index e9544822bf..8a844b3b5f 100644
> > --- a/src/backend/access/heap/heapam.c
> > +++ b/src/backend/access/heap/heapam.c
> > @@ -2106,7 +2106,6 @@ heap_multi_insert(Relation relation,
> TupleTableSlot **slots, int ntuples,
> > CommandId cid, int options,
> BulkInsertState bistate)
> > {
> > TransactionId xid = GetCurrentTransactionId();
> > - HeapTuple *heaptuples;
> > int i;
> > int ndone;
> > PGAlignedBlock scratch;
> > @@ -2115,6 +2114,10 @@ heap_multi_insert(Relation relation,
> TupleTableSlot **slots, int ntuples,
> > SizesaveFreeSpace;
> > boolneed_tuple_data =
> RelationIsLogicallyLogged(relation);
> > boolneed_cids =
> RelationIsAccessibleInLogicalDecoding(relation);
> > + /* Declare it as static to let this memory be not on stack. */
> > + static HeapTupleheaptuples[MAX_MULTI_INSERT_TUPLES];
> > +
> > + Assert(ntuples <= MAX_MULTI_INSERT_TUPLES);
> >
> > /* currently not needed (thus unsupported) for heap_multi_insert()
> */
> > AssertArg(!(options & HEAP_INSERT_NO_LOGICAL));
> > @@ -2124,7 +2127,6 @@ heap_multi_insert(Relation relation,
> TupleTableSlot **slots, int ntuples,
> >
> HEAP_DEFAULT_FILLFACTOR);
> >
> > /* Toast and set header data in all the slots */
> > - heaptuples = palloc(ntuples * sizeof(HeapTuple));
> > for (i = 0; i < ntuples; i++)
> > {
> > HeapTuple tuple;
>
> I don't think this is a good idea. We shouldn't unnecessarily allocate
> 8KB on the stack. Is there any actual evidence this is a performance
> benefit? To me this just seems like it'll reduce the flexibility of the
>
Previous heaptuples is palloc-ed in each batch, which should be slower than
pre-allocated & reusing memory in theory.
API, without any benefit. I'll also note that you've apparently not
> updated tableam.h to document this new restriction.
>
Yes it should be moved from heapam.h to that file along with the 65535
definition.
Re: Batch insert in CTAS/MatView code
Hi,
On 2019-09-09 18:31:54 +0800, Paul Guo wrote:
> diff --git a/src/backend/access/heap/heapam.c
> b/src/backend/access/heap/heapam.c
> index e9544822bf..8a844b3b5f 100644
> --- a/src/backend/access/heap/heapam.c
> +++ b/src/backend/access/heap/heapam.c
> @@ -2106,7 +2106,6 @@ heap_multi_insert(Relation relation, TupleTableSlot
> **slots, int ntuples,
> CommandId cid, int options, BulkInsertState
> bistate)
> {
> TransactionId xid = GetCurrentTransactionId();
> - HeapTuple *heaptuples;
> int i;
> int ndone;
> PGAlignedBlock scratch;
> @@ -2115,6 +2114,10 @@ heap_multi_insert(Relation relation, TupleTableSlot
> **slots, int ntuples,
> SizesaveFreeSpace;
> boolneed_tuple_data = RelationIsLogicallyLogged(relation);
> boolneed_cids =
> RelationIsAccessibleInLogicalDecoding(relation);
> + /* Declare it as static to let this memory be not on stack. */
> + static HeapTupleheaptuples[MAX_MULTI_INSERT_TUPLES];
> +
> + Assert(ntuples <= MAX_MULTI_INSERT_TUPLES);
>
> /* currently not needed (thus unsupported) for heap_multi_insert() */
> AssertArg(!(options & HEAP_INSERT_NO_LOGICAL));
> @@ -2124,7 +2127,6 @@ heap_multi_insert(Relation relation, TupleTableSlot
> **slots, int ntuples,
>
>HEAP_DEFAULT_FILLFACTOR);
>
> /* Toast and set header data in all the slots */
> - heaptuples = palloc(ntuples * sizeof(HeapTuple));
> for (i = 0; i < ntuples; i++)
> {
> HeapTuple tuple;
I don't think this is a good idea. We shouldn't unnecessarily allocate
8KB on the stack. Is there any actual evidence this is a performance
benefit? To me this just seems like it'll reduce the flexibility of the
API, without any benefit. I'll also note that you've apparently not
updated tableam.h to document this new restriction.
Greetings,
Andres Freund
Re: Batch insert in CTAS/MatView code
Hi, On 2019-09-26 10:43:27 -0300, Alvaro Herrera wrote: > On 2019-Sep-25, Asim R P wrote: > > > I reviewed your patch today. It looks good overall. My concern is that > > the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic > > place such as createas.c, we should be using generic tableam API > > only. Indeed. > > However, I can also see that there is no better alternative. We need to > > compute the size of accumulated tuples so far, in order to decide whether > > to stop accumulating tuples. There is no convenient way to obtain the > > length of the tuple, given a slot. How about making that decision solely > > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call > > altogether? > > ... maybe we should add a new operation to slots, that returns the > (approximate?) size of a tuple? Hm, I'm not convinced that it's worth adding that as a dedicated operation. It's not that clear what it'd exactly mean anyway - what would it measure? As referenced in the slot? As if it were stored on disk? etc? I wonder if the right answer wouldn't be to just measure the size of a memory context containing the batch slots, or something like that. > That would make this easy. (I'm not sure however what to do about > TOAST considerations -- is it size in memory that we're worried > about?) The in-memory size is probably fine, because in all likelihood the toasted cols are just going to point to on-disk datums, no? > Also: > > + myState->mi_slots_size >= 65535) > > This magic number should be placed in a define next to the other one, > but I'm not sure that heapam.h is a good location, since surely this > applies to matviews in other table AMs too. Right. I think it'd be better to move this into an AM independent place. Greetings, Andres Freund
Re: Batch insert in CTAS/MatView code
On Thu, Sep 26, 2019 at 7:13 PM Alvaro Herrera wrote: > > On 2019-Sep-25, Asim R P wrote: > > > I reviewed your patch today. It looks good overall. My concern is that > > the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic > > place such as createas.c, we should be using generic tableam API only. > > However, I can also see that there is no better alternative. We need to > > compute the size of accumulated tuples so far, in order to decide whether > > to stop accumulating tuples. There is no convenient way to obtain the > > length of the tuple, given a slot. How about making that decision solely > > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call > > altogether? > > ... maybe we should add a new operation to slots, that returns the > (approximate?) size of a tuple? That would make this easy. (I'm not > sure however what to do about TOAST considerations -- is it size in > memory that we're worried about?) That will help. For slots containing heap tuples, heap_compute_data_size() is what we need. Approximate size is better than nothing. In case of CTAS, we are dealing with slots returned by a scan node. Wouldn't TOAST datums be already expanded in those slots? Asim
Re: Batch insert in CTAS/MatView code
On Thu, Sep 26, 2019 at 9:43 PM Alvaro Herrera wrote: > On 2019-Sep-25, Asim R P wrote: > > > I reviewed your patch today. It looks good overall. My concern is that > > the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic > > place such as createas.c, we should be using generic tableam API only. > > However, I can also see that there is no better alternative. We need to > > compute the size of accumulated tuples so far, in order to decide whether > > to stop accumulating tuples. There is no convenient way to obtain the > > length of the tuple, given a slot. How about making that decision solely > > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple > call > > altogether? > > ... maybe we should add a new operation to slots, that returns the > (approximate?) size of a tuple? That would make this easy. (I'm not > sure however what to do about TOAST considerations -- is it size in > memory that we're worried about?) > > Also: > > + myState->mi_slots_size >= 65535) > > This magic number should be placed in a define next to the other one, > but I'm not sure that heapam.h is a good location, since surely this > applies to matviews in other table AMs too. > > yes defining 65535 seems better. Let's fix this one later when having more feedback. Thanks.
Re: Batch insert in CTAS/MatView code
Asim Thanks for the review. On Wed, Sep 25, 2019 at 6:39 PM Asim R P wrote: > > > > On Mon, Sep 9, 2019 at 4:02 PM Paul Guo wrote: > > > > So in theory > > we should not worry about additional tuple copy overhead now, and then I > tried the patch without setting > > multi-insert threshold as attached. > > > > I reviewed your patch today. It looks good overall. My concern is that > the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic > place such as createas.c, we should be using generic tableam API only. > However, I can also see that there is no better alternative. We need to > compute the size of accumulated tuples so far, in order to decide whether > to stop accumulating tuples. There is no convenient way to obtain the > length of the tuple, given a slot. How about making that decision solely > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call > altogether? > For heapam, ExecFetchSlotHeapTuple() will be called again in heap_multi_insert() to prepare the final multi-insert. if we check ExecFetchSlotHeapTuple(), we could find that calling it multiple time just involves very very few overhead for the BufferHeapTuple case. Note for virtual tuple case the 2nd ExecFetchSlotHeapTuple() call still copies slot contents, but we've called ExecCopySlot(batchslot, slot); to copy to a BufferHeap case so no worries for the virtual tuple case (as a source). Previously (long ago) I probably understood the code incorrectly so had the concern also. I used sampling to do that (for variable-length tuple), but now apparently we do not need that. > > The multi insert copy code deals with index tuples also, which I don't see > in the patch. Don't we need to consider populating indexes? > create table as/create mat view DDL does not involve index creation for the table/matview. The code seems to be able to used in RefreshMatView also, for that we need to consider if we use multi-insert in that code.
Re: Batch insert in CTAS/MatView code
On 2019-Sep-25, Asim R P wrote: > I reviewed your patch today. It looks good overall. My concern is that > the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic > place such as createas.c, we should be using generic tableam API only. > However, I can also see that there is no better alternative. We need to > compute the size of accumulated tuples so far, in order to decide whether > to stop accumulating tuples. There is no convenient way to obtain the > length of the tuple, given a slot. How about making that decision solely > based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call > altogether? ... maybe we should add a new operation to slots, that returns the (approximate?) size of a tuple? That would make this easy. (I'm not sure however what to do about TOAST considerations -- is it size in memory that we're worried about?) Also: + myState->mi_slots_size >= 65535) This magic number should be placed in a define next to the other one, but I'm not sure that heapam.h is a good location, since surely this applies to matviews in other table AMs too. -- Álvaro Herrerahttps://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: Batch insert in CTAS/MatView code
On Mon, Sep 9, 2019 at 4:02 PM Paul Guo wrote: > > So in theory > we should not worry about additional tuple copy overhead now, and then I tried the patch without setting > multi-insert threshold as attached. > I reviewed your patch today. It looks good overall. My concern is that the ExecFetchSlotHeapTuple call does not seem appropriate. In a generic place such as createas.c, we should be using generic tableam API only. However, I can also see that there is no better alternative. We need to compute the size of accumulated tuples so far, in order to decide whether to stop accumulating tuples. There is no convenient way to obtain the length of the tuple, given a slot. How about making that decision solely based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call altogether? The multi insert copy code deals with index tuples also, which I don't see in the patch. Don't we need to consider populating indexes? Asim
Re: Batch insert in CTAS/MatView code
On Fri, Aug 2, 2019 at 2:55 AM Heikki Linnakangas wrote: > On 17/06/2019 15:53, Paul Guo wrote: > > I noticed that to do batch insert, we might need additional memory copy > > sometimes comparing with "single insert" > > (that should be the reason that we previously saw a bit regressions) so a > > good solution seems to fall back > > to "single insert" if the tuple length is larger than a threshold. I set > > this as 2000 after quick testing. > > Where does the additional memory copy come from? Can we avoid doing it > in the multi-insert case? Hi Heikki, Sorry for the late reply. I took some time on looking at & debugging the code of TupleTableSlotOps of various TupleTableSlot types carefully, especially the BufferHeapTupleTableSlot case on which we seemed to see regression if no threshold is set, also debugging & testing more of the CTAS case. I found my previous word "additional memory copy" (mainly tuple content copy against single insert) is wrong based on the latest code (probably is wrong also with previous code). So in theory we should not worry about additional tuple copy overhead now, and then I tried the patch without setting multi-insert threshold as attached. To make test results more stable, this time I run a simple ' select count(*) from tbl' before each CTAS to warm up the shared buffer, run checkpoint before each CTAS, disable autovacuum by setting 'autovacuum = off', set larger shared buffers (but < 25% of total memory which is recommended by PG doc) so that CTAS all hits shared buffer read if there exists warm buffers (double-checked via explain(analyze, buffers)). These seem to be reasonable for performance testing. Each kind of CTAS testing is run three times (Note before each run we do warm up and checkpoint as mentioned). I mainly tested the t12 (normal table with tuple size ~ 2k) case since for others our patch either performs better or similarly. Patch: 1st_run 2nd_run3rd_run t12_BufferHeapTuple 7883.400 7549.9668090.080 t12_Virtual 8041.637 8191.3178182.404 Baseline: 1st_run 2nd_run3rd_run t12_BufferHeapTuple: 8264.290 7508.410 7681.702 t12_Virtual 8167.792 7970.537 8106.874 I actually roughly tested other tables we mentioned also (t11 and t14) - the test results and conclusions are same. t12_BufferHeapTuple means: create table tt as select * from t12; t12_Virtual means: create table tt as select *partial columns* from t12; So it looks like for t12 the results between our code and baseline are similar so not setting threshoud seem to be good though it looks like t12_BufferHeapTuple test results varies a lot (at most 0.5 seconds) for both our patch and baseline vs the virtual case which is quite stable. This actually confused me a bit given we've cached the source table in shared buffers. I suspected checkpoint affects, so I disabled checkpoint by setting max_wal_size = 3000 during CTAS, the BufferHeapTuple case (see below) still varies some. I'm not sure what's the reason but this does not seem to a be blocker for the patch. Patch: 1st_run 2nd_run3rd_run t12_BufferHeapTuple 7717.3047413.2597452.773 t12_Virtual 7445.742 7483.148 7593.583 Baseline: 1st_run 2nd_run3rd_run t12_BufferHeapTuple 8186.302 7736.541 7759.056 t12_Virtual 8004.880 8096.712 7961.483 v4-0001-Multi-insert-in-Create-Table-As.patch Description: Binary data
Re: Batch insert in CTAS/MatView code
On 17/06/2019 15:53, Paul Guo wrote: I noticed that to do batch insert, we might need additional memory copy sometimes comparing with "single insert" (that should be the reason that we previously saw a bit regressions) so a good solution seems to fall back to "single insert" if the tuple length is larger than a threshold. I set this as 2000 after quick testing. Where does the additional memory copy come from? Can we avoid doing it in the multi-insert case? - Heikki
Re: Batch insert in CTAS/MatView code
On Mon, Jun 17, 2019 at 8:53 PM Paul Guo wrote:
> Hi all,
>
> I've been working other things until recently I restarted the work,
> profiling & refactoring the code.
> It's been a long time since the last patch was proposed. The new patch has
> now been firstly refactored due to
> 4da597edf1bae0cf0453b5ed6fc4347b6334dfe1 (Make TupleTableSlots extensible,
> finish split of existing slot type).
>
> Now that TupleTableSlot, instead of HeapTuple is one argument of
> intorel_receive() so we can not get the
> tuple length directly. This patch now gets the tuple length if we know all
> columns are with fixed widths, else
> we calculate an avg. tuple length using the first MAX_MULTI_INSERT_SAMPLES
> (defined as 1000) tuples
> and use for the total length of tuples in a batch.
>
> I noticed that to do batch insert, we might need additional memory copy
> sometimes comparing with "single insert"
> (that should be the reason that we previously saw a bit regressions) so a
> good solution seems to fall back
> to "single insert" if the tuple length is larger than a threshold. I set
> this as 2000 after quick testing.
>
> To make test stable and strict, I run checkpoint before each ctas, the
> test script looks like this:
>
> checkpoint;
> \timing
> create table tt as select a,b,c from t11;
> \timing
> drop table tt;
>
> Also previously I just tested the BufferHeapTupleTableSlot (i.e. create
> table tt as select * from t11),
> this time I test VirtualTupleTableSlot (i.e. create table tt as select
> a,b,c from t11) additionally.
> It seems that VirtualTupleTableSlot is very common in real cases.
>
> I tested four kinds of tables, see below SQLs.
>
> -- tuples with small size.
> create table t11 (a int, b int, c int, d int);
> insert into t11 select s,s,s,s from generate_series(1, 1000) s;
> analyze t11;
>
> -- tuples that are untoasted and tuple size is 1984 bytes.
> create table t12 (a name, b name, c name, d name, e name, f name, g name,
> h name, i name, j name, k name, l name, m name, n name, o name, p name, q
> name, r name, s name, t name, u name, v name, w name, x name, y name, z
> name, a1 name, a2 name, a3 name, a4 name, a5 name);
> insert into t12 select 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
> 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
> 'z', 'a', 'b', 'c', 'd', 'e' from generate_series(1, 50);
> analyze t12;
>
> -- tuples that are untoasted and tuple size is 2112 bytes.
> create table t13 (a name, b name, c name, d name, e name, f name, g name,
> h name, i name, j name, k name, l name, m name, n name, o name, p name, q
> name, r name, s name, t name, u name, v name, w name, x name, y name, z
> name, a1 name, a2 name, a3 name, a4 name, a5 name, a6 name, a7 name);
> insert into t13 select 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
> 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
> 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g' from generate_series(1, 50);
> analyze t13;
>
> -- tuples that are toastable and tuple compressed size is 1084.
> create table t14 (a text, b text, c text, d text, e text, f text, g text,
> h text, i text, j text, k text, l text, m text, n text, o text, p text, q
> text, r text, s text, t text, u text, v text, w text, x text, y text, z
> text);
> insert into t14 select i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i,
> i, i, i, i, i, i, i, i, i from (select repeat('123456789', 1) from
> generate_series(1,5000)) i;
> analyze t14;
>
>
> I also tested two scenarios for each testing.
>
> One is to clean up all kernel caches (page & inode & dentry on Linux)
> using the command below and then run the test,
> sync; echo 3 > /proc/sys/vm/drop_caches
> After running all tests all relation files will be in kernel cache (my
> test system memory is large enough to accommodate all relation files),
> then I run the tests again. I run like this because in real scenario the
> result of the test should be among the two results. Also I rerun
> each test and finally I calculate the average results as the experiment
> results. Below are some results:
>
>
> scenario1: All related kernel caches are cleaned up (note the first two
> columns are time with second).
>
> baselinepatch diff% SQL
>
>
>
>
> 10.15.5744.85% create table tt as select * from t11;
>
> 10.75.5248.41% create table tt as select a,b,c from t11;
>
> 9.5710.2-6.58% create table tt as select * from t12;
>
> 9.648.6310.48% create table tt as select
> a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,a1,a2,a3,a4 from t12;
>
> 14.214.46 -1.83% create table tt as select * from t13;
>
> 11.88 12.05 -1.43% create table tt as select
> a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,a1,a2,a3,a4,a5,a6 from
> t13;
>
> 3.173.25-2.52% create table tt as select * from t14;
>
>
> 2.933.12-6.48% create table tt as select
>
Re: Batch insert in CTAS/MatView code
Hi all,
I've been working other things until recently I restarted the work,
profiling & refactoring the code.
It's been a long time since the last patch was proposed. The new patch has
now been firstly refactored due to
4da597edf1bae0cf0453b5ed6fc4347b6334dfe1 (Make TupleTableSlots extensible,
finish split of existing slot type).
Now that TupleTableSlot, instead of HeapTuple is one argument of
intorel_receive() so we can not get the
tuple length directly. This patch now gets the tuple length if we know all
columns are with fixed widths, else
we calculate an avg. tuple length using the first MAX_MULTI_INSERT_SAMPLES
(defined as 1000) tuples
and use for the total length of tuples in a batch.
I noticed that to do batch insert, we might need additional memory copy
sometimes comparing with "single insert"
(that should be the reason that we previously saw a bit regressions) so a
good solution seems to fall back
to "single insert" if the tuple length is larger than a threshold. I set
this as 2000 after quick testing.
To make test stable and strict, I run checkpoint before each ctas, the test
script looks like this:
checkpoint;
\timing
create table tt as select a,b,c from t11;
\timing
drop table tt;
Also previously I just tested the BufferHeapTupleTableSlot (i.e. create
table tt as select * from t11),
this time I test VirtualTupleTableSlot (i.e. create table tt as select
a,b,c from t11) additionally.
It seems that VirtualTupleTableSlot is very common in real cases.
I tested four kinds of tables, see below SQLs.
-- tuples with small size.
create table t11 (a int, b int, c int, d int);
insert into t11 select s,s,s,s from generate_series(1, 1000) s;
analyze t11;
-- tuples that are untoasted and tuple size is 1984 bytes.
create table t12 (a name, b name, c name, d name, e name, f name, g name, h
name, i name, j name, k name, l name, m name, n name, o name, p name, q
name, r name, s name, t name, u name, v name, w name, x name, y name, z
name, a1 name, a2 name, a3 name, a4 name, a5 name);
insert into t12 select 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
'z', 'a', 'b', 'c', 'd', 'e' from generate_series(1, 50);
analyze t12;
-- tuples that are untoasted and tuple size is 2112 bytes.
create table t13 (a name, b name, c name, d name, e name, f name, g name, h
name, i name, j name, k name, l name, m name, n name, o name, p name, q
name, r name, s name, t name, u name, v name, w name, x name, y name, z
name, a1 name, a2 name, a3 name, a4 name, a5 name, a6 name, a7 name);
insert into t13 select 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g' from generate_series(1, 50);
analyze t13;
-- tuples that are toastable and tuple compressed size is 1084.
create table t14 (a text, b text, c text, d text, e text, f text, g text, h
text, i text, j text, k text, l text, m text, n text, o text, p text, q
text, r text, s text, t text, u text, v text, w text, x text, y text, z
text);
insert into t14 select i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i,
i, i, i, i, i, i, i, i, i from (select repeat('123456789', 1) from
generate_series(1,5000)) i;
analyze t14;
I also tested two scenarios for each testing.
One is to clean up all kernel caches (page & inode & dentry on Linux) using
the command below and then run the test,
sync; echo 3 > /proc/sys/vm/drop_caches
After running all tests all relation files will be in kernel cache (my test
system memory is large enough to accommodate all relation files),
then I run the tests again. I run like this because in real scenario the
result of the test should be among the two results. Also I rerun
each test and finally I calculate the average results as the experiment
results. Below are some results:
scenario1: All related kernel caches are cleaned up (note the first two
columns are time with second).
baselinepatch diff% SQL
10.15.5744.85% create table tt as select * from t11;
10.75.5248.41% create table tt as select a,b,c from t11;
9.5710.2-6.58% create table tt as select * from t12;
9.648.6310.48% create table tt as select
a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,a1,a2,a3,a4 from t12;
14.214.46 -1.83% create table tt as select * from t13;
11.88 12.05 -1.43% create table tt as select
a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,a1,a2,a3,a4,a5,a6 from
t13;
3.173.25-2.52% create table tt as select * from t14;
2.933.12-6.48% create table tt as select
a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y from t14;
scenario2: all related kernel caches are populated after previous testing.
baselinepatch diff% SQL
9.6 4.9748.23% create table tt as select * from t11;
10.41 5.3248.90% create table tt as
Re: Batch insert in CTAS/MatView code
On Mon, Mar 11, 2019 at 2:58 AM David Fetter wrote: > On Wed, Mar 06, 2019 at 10:06:27PM +0800, Paul Guo wrote: > > Hello, Postgres hackers, > > > > The copy code has used batch insert with function heap_multi_insert() to > > speed up. It seems that Create Table As or Materialized View could > leverage > > that code also to boost the performance also. Attached is a patch to > > implement that. > > This is great! > > Is this optimization doable for multi-row INSERTs, either with tuples > spelled out in the body of the query or in constructs like INSERT ... > SELECT ...? > Yes. That's "batch insert" in the ModifyTable nodes which I mentioned in the first email. By the way, batch is a usual optimization mechanism for iteration kind model (like postgres executor), so batch should benefit many executor nodes in theory also. > > Best, > David. > -- > David Fetter > https://urldefense.proofpoint.com/v2/url?u=http-3A__fetter.org_=DwIBAg=lnl9vOaLMzsy2niBC8-h_K-7QJuNJEsFrzdndhuJ3Sw=Usi0ex6Ch92MsB5QQDgYFw=wgGDTDFzZV7nnMm0NFt-yGKmm_KZk18RXKP9HL8h6UE=tnaoLdajjR0Ew-93XUliHW1FUspVl09pIFd9aXxvqc8= > Phone: +1 415 235 3778 > > Remember to vote! > Consider donating to Postgres: http://www.postgresql.org/about/donate >
Re: Batch insert in CTAS/MatView code
On Wed, Mar 06, 2019 at 10:06:27PM +0800, Paul Guo wrote: > Hello, Postgres hackers, > > The copy code has used batch insert with function heap_multi_insert() to > speed up. It seems that Create Table As or Materialized View could leverage > that code also to boost the performance also. Attached is a patch to > implement that. This is great! Is this optimization doable for multi-row INSERTs, either with tuples spelled out in the body of the query or in constructs like INSERT ... SELECT ...? Best, David. -- David Fetter http://fetter.org/ Phone: +1 415 235 3778 Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate
Re: Batch insert in CTAS/MatView code
Sorry for the late reply. To Michael. Thank you. I know this commitfest is ongoing and I'm not targeting for this. On Thu, Mar 7, 2019 at 4:54 PM Heikki Linnakangas wrote: > On 06/03/2019 22:06, Paul Guo wrote: > > The patch also modifies heap_multi_insert() a bit to do a bit further > > code-level optimization by using static memory, instead of using memory > > context and dynamic allocation. > > If toasting is required, heap_prepare_insert() creates a palloc'd tuple. > That is still leaked to the current memory context. > > Thanks. I checked the code for that but apparently, I missed that one. I'll see what proper context can be used for CTAS. For copy code maybe just revert my change. > Leaking into the current memory context is not a bad thing, because > resetting a memory context is faster than doing a lot of pfree() calls. > The callers just need to be prepared for that, and use a short-lived > memory context. > > > By the way, while looking at the code, I noticed that there are 9 local > > arrays with large length in toast_insert_or_update() which seems to be a > > risk of stack overflow. Maybe we should put it as static or global. > > Hmm. We currently reserve 512 kB between the kernel's limit, and the > limit we check in check_stack_depth(). See STACK_DEPTH_SLOP. Those > arrays add up to 52800 bytes on a 64-bit maching, if I did my math > right. So there's still a lot of headroom. I agree that it nevertheless > seems a bit excessive, though. > I was worried about some recursive calling of it, but probably there should be no worry for toast_insert_or_update(). > > With the patch, > > > > Time: 4728.142 ms (00:04.728) > > Time: 14203.983 ms (00:14.204) > > Time: 1008.669 ms (00:01.009) > > > > Baseline, > > Time: 11096.146 ms (00:11.096) > > Time: 13106.741 ms (00:13.107) > > Time: 1100.174 ms (00:01.100) > > Nice speedup! > > > While for toast and large column size there is < 10% decrease but for > > small column size the improvement is super good. Actually if I hardcode > > the batch count as 4 all test cases are better but the improvement for > > small column size is smaller than that with current patch. Pretty much > > the number 4 is quite case specific so I can not hardcode that in the > > patch. Of course we could further tune that but the current value seems > > to be a good trade-off? > > Have you done any profiling, on why the multi-insert is slower with > large tuples? In principle, I don't see why it should be slower. > Thanks for the suggestion. I'll explore a bit more on this. > > - Heikki >
Re: Batch insert in CTAS/MatView code
On 06/03/2019 22:06, Paul Guo wrote: The patch also modifies heap_multi_insert() a bit to do a bit further code-level optimization by using static memory, instead of using memory context and dynamic allocation. If toasting is required, heap_prepare_insert() creates a palloc'd tuple. That is still leaked to the current memory context. Leaking into the current memory context is not a bad thing, because resetting a memory context is faster than doing a lot of pfree() calls. The callers just need to be prepared for that, and use a short-lived memory context. By the way, while looking at the code, I noticed that there are 9 local arrays with large length in toast_insert_or_update() which seems to be a risk of stack overflow. Maybe we should put it as static or global. Hmm. We currently reserve 512 kB between the kernel's limit, and the limit we check in check_stack_depth(). See STACK_DEPTH_SLOP. Those arrays add up to 52800 bytes on a 64-bit maching, if I did my math right. So there's still a lot of headroom. I agree that it nevertheless seems a bit excessive, though. With the patch, Time: 4728.142 ms (00:04.728) Time: 14203.983 ms (00:14.204) Time: 1008.669 ms (00:01.009) Baseline, Time: 11096.146 ms (00:11.096) Time: 13106.741 ms (00:13.107) Time: 1100.174 ms (00:01.100) Nice speedup! While for toast and large column size there is < 10% decrease but for small column size the improvement is super good. Actually if I hardcode the batch count as 4 all test cases are better but the improvement for small column size is smaller than that with current patch. Pretty much the number 4 is quite case specific so I can not hardcode that in the patch. Of course we could further tune that but the current value seems to be a good trade-off? Have you done any profiling, on why the multi-insert is slower with large tuples? In principle, I don't see why it should be slower. - Heikki
Re: Batch insert in CTAS/MatView code
Hi, On Wed, Mar 06, 2019 at 10:06:27PM +0800, Paul Guo wrote: > The copy code has used batch insert with function heap_multi_insert() to > speed up. It seems that Create Table As or Materialized View could leverage > that code also to boost the performance also. Attached is a patch to > implement that. That was done by Taylor (cc-ed) and me. Please note that we are currently in the last commit fest of Postgres 12, and it is too late to propose new features. Please feel free to add an entry to the commit fest happening afterwards. -- Michael signature.asc Description: PGP signature
Batch insert in CTAS/MatView code
Hello, Postgres hackers,
The copy code has used batch insert with function heap_multi_insert() to
speed up. It seems that Create Table As or Materialized View could leverage
that code also to boost the performance also. Attached is a patch to
implement that. That was done by Taylor (cc-ed) and me.
The patch also modifies heap_multi_insert() a bit to do a bit further
code-level optimization by using static memory, instead of using memory
context and dynamic allocation. For Modifytable->insert, it seems that
there are more limitations for batch insert (trigger, etc?) but it seems
that it is possible that we could do batch insert for the case that we
could do?
By the way, while looking at the code, I noticed that there are 9 local
arrays with large length in toast_insert_or_update() which seems to be a
risk of stack overflow. Maybe we should put it as static or global.
Here is a quick simple performance testing on a mirrorless Postgres
instance with the SQLs below. The tests cover tables with small column
length, large column length and toast.
-- tuples with small size.
drop table if exists t1;
create table t1 (a int);
insert into t1 select * from generate_series(1, 1000);
drop table if exists t2;
\timing
create table t2 as select * from t1;
\timing
-- tuples that are untoasted and data that is 1664 bytes wide
drop table if exists t1;
create table t1 (a name, b name, c name, d name, e name, f name, g name, h
name, i name, j name, k name, l name, m name, n name, o name, p name, q
name, r name, s name, t name, u name, v name, w name, x name, y name, z
name);
insert into t1 select 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y',
'z' from generate_series(1, 50);
drop table if exists t2;
\timing
create table t2 as select * from t1;
\timing
-- tuples that are toastable.
drop table if exists t1;
create table t1 (a text, b text, c text, d text, e text, f text, g text, h
text, i text, j text, k text, l text, m text, n text, o text, p text, q
text, r text, s text, t text, u text, v text, w text, x text, y text, z
text);
insert into t1 select i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i, i,
i, i, i, i, i, i, i, i from (select repeat('123456789', 1) from
generate_series(1,2000)) i;
drop table if exists t2;
\timing
create table t2 as select * from t1;
\timing
Here are the timing results:
With the patch,
Time: 4728.142 ms (00:04.728)
Time: 14203.983 ms (00:14.204)
Time: 1008.669 ms (00:01.009)
Baseline,
Time: 11096.146 ms (00:11.096)
Time: 13106.741 ms (00:13.107)
Time: 1100.174 ms (00:01.100)
While for toast and large column size there is < 10% decrease but for small
column size the improvement is super good. Actually if I hardcode the batch
count as 4 all test cases are better but the improvement for small column
size is smaller than that with current patch. Pretty much the number 4 is
quite case specific so I can not hardcode that in the patch. Of course we
could further tune that but the current value seems to be a good trade-off?
Thanks.
0001-Heap-batch-insert-for-CTAS.patch
Description: Binary data
