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Re: Using Expanded Objects other than Arrays from plpgsql 5+ messages / 2 participants [nested] [flat]
* Re: Using Expanded Objects other than Arrays from plpgsql @ 2024-10-21 03:29 Michel Pelletier <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: Michel Pelletier @ 2024-10-21 03:29 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: pgsql-general <[email protected]> On Sun, Oct 20, 2024 at 10:13 AM Tom Lane <[email protected]> wrote: > > I'm not sure. It seems certain that if the object is already expanded > (either R/W or R/O), the paths for that in plpgsql_exec_function could > be taken regardless of its specific type. > > But it seems like we could get an easy win by adjusting > plpgsql_exec_function along the lines of > > l. 549: > - if (!var->isnull && var->datatype->typisarray) > + if (!var->isnull) > > l. 564: > - else > + else if (var->datatype->typisarray) > > How far does that improve matters for you? > I tried this change and couldn't get it to work, on the next line: if (!var->isnull) { if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var->value))) var->value might not be a pointer, as it seems at least from my gdb scratching, but say an integer. This segfaults on non-array but non-expandable datum. I guess this gets back into knowing if a flat thing is expandable or not. I'm going to spend some more time looking at it, I haven't been in this corner of Postgres before. Another comment that caught my eye was this one: https://github.com/postgres/postgres/blob/master/src/pl/plpgsql/src/pl_exec.c#L8304 Not sure what the implication is there. -Michel ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Using Expanded Objects other than Arrays from plpgsql @ 2024-10-21 03:46 Tom Lane <[email protected]> parent: Michel Pelletier <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: Tom Lane @ 2024-10-21 03:46 UTC (permalink / raw) To: Michel Pelletier <[email protected]>; +Cc: pgsql-general <[email protected]> Michel Pelletier <[email protected]> writes: > On Sun, Oct 20, 2024 at 10:13 AM Tom Lane <[email protected]> wrote: >> But it seems like we could get an easy win by adjusting >> plpgsql_exec_function along the lines of >> ... > I tried this change and couldn't get it to work, on the next line: > if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var->value))) > var->value might not be a pointer, as it seems at least from my gdb > scratching, but say an integer. This segfaults on non-array but > non-expandable datum. Oh, duh --- the typisarray test serves to eliminate pass-by-value types. We need the same test that exec_assign_value makes, !var->datatype->typbyval, before it's safe to apply DatumGetPointer. So line 549 needs to be more like - if (!var->isnull && var->datatype->typisarray) + if (!var->isnull && !var->datatype->typbyval) > Another comment that caught my eye was this one: > https://github.com/postgres/postgres/blob/master/src/pl/plpgsql/src/pl_exec.c#L8304 > Not sure what the implication is there. Yeah, that's some more unfinished business. I'm not sure if it matters to your use-case or not. BTW, we probably should move this thread to pgsql-hackers. regards, tom lane ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Using Expanded Objects other than Arrays from plpgsql @ 2024-10-21 17:23 Michel Pelletier <[email protected]> parent: Tom Lane <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: Michel Pelletier @ 2024-10-21 17:23 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: [email protected] On Sun, Oct 20, 2024 at 8:46 PM Tom Lane <[email protected]> wrote: > Michel Pelletier <[email protected]> writes: > > On Sun, Oct 20, 2024 at 10:13 AM Tom Lane <[email protected]> wrote: > (from thread https://www.postgresql.org/message-id/CACxu%3DvJaKFNsYxooSnW1wEgsAO5u_v1XYBacfVJ14wgJV_PYeg%40mail.g... ) > >> But it seems like we could get an easy win by adjusting > >> plpgsql_exec_function along the lines of > >> ... > > > I tried this change and couldn't get it to work, on the next line: > > if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var->value))) > > var->value might not be a pointer, as it seems at least from my gdb > > scratching, but say an integer. This segfaults on non-array but > > non-expandable datum. > > We need the same test that exec_assign_value makes, > !var->datatype->typbyval, before it's safe to apply DatumGetPointer. > So line 549 needs to be more like > > - if (!var->isnull && var->datatype->typisarray) > + if (!var->isnull && !var->datatype->typbyval) > > > Another comment that caught my eye was this one: > > > https://github.com/postgres/postgres/blob/master/src/pl/plpgsql/src/pl_exec.c#L8304 > > Not sure what the implication is there. > > Yeah, that's some more unfinished business. I'm not sure if it > matters to your use-case or not. > > BTW, we probably should move this thread to pgsql-hackers. And here we are, thanks for your help on this Tom. For some thread switching context for others, I'm writing a postgres extension that wraps the SuiteSparse:GraphBLAS API and provides new types for sparse and dense matrices and vectors. It's like a combination of numpy and scipy.sparse but for Postgres with an emphasis on graph analytics as sparse adjacency matrices using linear algebra. I use the expandeddatum API to flatten and expand on disk compressed representations of these objects into "live" in-memory objects managed by SuiteSparse. All GraphBLAS objects are opaque handles, and my expanded objects are essentially a box around this handle. I use memory context callbacks to free the handles when the memory context of the box is freed. This works very well and I've made a lot of progress on creating a very clean algebraic API, here are the doctests for matrices, this is all generated from live code! https://onesparse.github.io/OneSparse/test_matrix_header/ Doing some benchmarking I noticed that when writing some simple graph algorithms in plpgsql, my objects were being constantly flattened and expanded. Posting my question above to pgsql-general Tom gave me some tips and suggested I move the thread here. My non-expert summary: plpgsql only optimizes for expanded objects if they are arrays. Non array expanded objects get flattened/expanded on every use. For large matrices and vectors this is very expensive. Ideally I'd like to expand my object, use it throughout the function, return it to another function that may use it, and only flatten it when it goes to disk or it's completely unavoidable. The comment in expandeddatum.h really kind of sells this as one of the main features: * An expanded object is meant to survive across multiple operations, but * not to be enormously long-lived; for example it might be a local variable * in a PL/pgSQL procedure. So its extra bulk compared to the on-disk format * is a worthwhile trade-off. In my case it's not a question of saving bulk, the on disk representation of a matrix is not useful at compute time, it needs to be expanded (using GraphBLAS's serialize/deserialize API) for it to be usable for matrix operations like matmul. In most cases algorithms using these objects iterate in a loop, doing various algebraic operations almost always involving a matmul until they converge on a stable solution or they exhaust the input elements. Here for example is a "minimum parent BFS" that takes a graph and a starting node, and traverses the graph breadth first, computing a vector of every node and its minimum parent id. CREATE OR REPLACE FUNCTION bfs(graph matrix, start_node bigint) > RETURNS vector LANGUAGE plpgsql AS > $$ > DECLARE > bfs_vector vector = vector('int32'); > next_vector vector = vector('int32'); > BEGIN > bfs_vector = set_element(bfs_vector, start_node, 1); > WHILE sssp_vector != next_vector LOOP > next_vector = dup(bfs_vector); > bfs_vector = vxm(bfs_vector, graph, 'any_secondi_int32', > w=>bfs_vector, accum=>'min_int32'); > END LOOP; > RETURN bfs_vector; > end; > $$; > (If you're wondering "Why would anyone do it this way" it's because SuiteSparse is optimized for parallel sparse matrix multiplication and has a JIT compiler that can target multiple architectures, at the moment CPUs and CUDA GPUs. Reusing the same Linear Algebra already prevalent in graph theory means not having to think about any low level implementation issues and having code that is completely portable from CPU to GPU or other accelerators). So, I made the two small changes Tom suggested above and I have them in a side fork here: https://github.com/postgres/postgres/compare/master...michelp:postgres-upstream:michelp-flatless#dif... Good news, my code still works, but bad news is there is still a lot of flattening/expanding/freeing going on at multiple points in each iteration of the algorithm. I'll note too that: BEGIN bfs_vector = set_element(sssp_vector, start_node, 1); I'd prefer that to not be an assignment, set_element mutates the object (I eventually plan to support subscripting syntax like bfs_vector[start_node] = 1) same with: bfs_vector = vxm(bfs_vector, graph, 'any_secondi_int32', w=>bfs_vector, accum=>'min_int32'); This matmul mutates bfs_vector, I shouldn't need to reassign it back but at the moment it seems necessary otherwise the mutations are lost but this costs a full flatten/expand cycle. Short term my goal is to optimize plpgsql so that my objects stay expanded for the life of the function. Long term there's some "unfinished business" to use Tom's words around the expandeddatum API. I'm not really qualified to speak on these issue but this is my understanding of some of them: - plpgsql knows how to expand arrays and is hardwired for it, but how would it know how to expand other expandable types? - Issues with exec_check_rw_parameter also being hardwired to only optimize expanded objects for array append and prepend, I suspect this has something to do with my issue above about mutating objects in place. I may have missed something but hopefully that brings anyone up to speed interested in this topic. -Michel ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Using Expanded Objects other than Arrays from plpgsql @ 2024-10-22 19:33 Tom Lane <[email protected]> parent: Michel Pelletier <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: Tom Lane @ 2024-10-22 19:33 UTC (permalink / raw) To: Michel Pelletier <[email protected]>; +Cc: [email protected] Michel Pelletier <[email protected]> writes: > Doing some benchmarking I noticed that when writing some simple graph > algorithms in plpgsql, my objects were being constantly flattened and > expanded. Posting my question above to pgsql-general Tom gave me some tips > and suggested I move the thread here. > My non-expert summary: plpgsql only optimizes for expanded objects if they > are arrays. Non array expanded objects get flattened/expanded on every > use. For large matrices and vectors this is very expensive. Ideally I'd > like to expand my object, use it throughout the function, return it to > another function that may use it, and only flatten it when it goes to disk > or it's completely unavoidable. Right. My recollection is that when we first invented expanded objects, we only implemented expanded arrays, and so it seemed premature to try to define generalized APIs. So that went on the back burner until we got some more cases to look at. But now we also have expanded records, and with your use-case as an example of an extension trying to do similar things, I feel like we have enough examples to move forward. As far as the hack we were discussing upthread goes, I realized that it should test for typlen == -1 not just !typbyval, since the VARATT_IS_EXTERNAL_EXPANDED_RW test requires that there be a length word. With that fix and some comment updates, it looks like the attached. I'm inclined to just go ahead and push that. It won't move the needle hugely far, but it will help, and it seems simple and safe. To make more progress, there are basically two areas that we need to look at: 1. exec_assign_value() has hard-wired knowledge that it's a good idea to expand an array that's being assigned to a plpgsql variable, and likewise hard-wired knowledge that calling expand_array() is how to do that. The bit in plpgsql_exec_function() that we're patching in the attached is the same thing, but for the initial assignment of a function input parameter to a plpgsql variable. At the time this was written I was quite unsure that forcible expansion would be a net win, but the code is nine years old now and there's been few or no performance complaints. So maybe it's okay to decide that "always expand expandable types during assignment" is a suitable policy across the board, and we don't need to figure out a smarter rule. It sounds like that'd probably be a win for your application, which gives me more faith in the idea than I would've had before. That leaves the problem of how to find the right code to call to do the expansion. Clearly, we need to attach something to data types to make that possible. My first thought was to invent a pg_type column (and CREATE TYPE/ALTER TYPE options, and pg_dump support, yadda yadda) containing the OID of a function corresponding to expand_array(). However, that work would have to be done again the next time we think of something we'd like to know about a data type. So now I'm thinking that we should steal ideas from the "prosupport" API (see src/include/nodes/supportnodes.h) and invent a concept of a "type support" function that can handle an extensible set of different requests. The first one would be to pass back the address of an expansion function comparable to expand_array(), if the type supports being converted to an expanded object. 2. Most of the performance gold is hidden in deciding when we can optimize operations on expanded objects that look like plpgsql_var := f(plpgsql_var, other-parameters); by passing a R/W rather than R/O expanded pointer to f() and letting it munge the expanded object in-place. If we fail to do that then f() has to construct a new expanded object for its result. It's probably still better off getting a R/O pointer than a flat object, but nonetheless we fail to avoid a lot of data copying. The difficulty here is that we do not want to change the normal naive semantics of such an assignment, in particular "if f() throws an error then the value of plpgsql_var has not been modified". This means that we can only optimize when the R/W parameter is to be passed to the top-level function of the expression (else, some function called later could throw an error and ruin things). Furthermore, we need a guarantee from f() that it will not throw an error after modifying the value. As things stand, plpgsql has hard-wired knowledge that array_subscript_handler(), array_append(), and array_prepend() are safe in that way, but it knows nothing about anything else. So one route to making things better seems fairly clear: invent a new prosupport request that asks whether the function is prepared to make such a guarantee. I wonder though if you can guarantee any such thing for your functions, when you are relying on a library that's probably not designed with such a restriction in mind. If this won't work then we need a new concept. One idea I was toying with is that it doesn't matter if f() throws an error so long as the plpgsql function is not executing within an exception block: if the error propagates out of the plpgsql function then we no longer care about the value of the variable. That would very substantially weaken the requirements on how f() is implemented. I'm not sure that we could make this work across multiple levels of plpgsql functions (that is, if the value of the variable ultimately resides in some outer function) but right now that's not an issue since no plpgsql function as such would ever promise to be safe, thus it would never receive a R/W pointer to some outer function's variable. > same with: > bfs_vector = vxm(bfs_vector, graph, 'any_secondi_int32', > w=>bfs_vector, accum=>'min_int32'); > This matmul mutates bfs_vector, I shouldn't need to reassign it back but at > the moment it seems necessary otherwise the mutations are lost but this > costs a full flatten/expand cycle. I'm not hugely excited about that. We could imagine extending this concept to INOUT parameters of procedures, but it doesn't seem like that buys anything except a small notational savings. Maybe it would work to allow multiple parameters of a procedure to be passed as R/W, whereas we're restricted to one for the function-notation method. So possibly there's a gain there but I'm not sure how big. BTW, if I understand your example correctly then bfs_vector is being passed to vxm() twice. This brings up an interesting point: if we pass the first instance as R/W, and vxm() manipulates it, then the changes would also be visible in its other parameter "w". This is certainly not per normal semantics. A "safe" function would have to either not have any possibility that two parameters could refer to the same object, or be coded in a way that made it impervious to this issue --- in your example, it couldn't look at "w" anymore once it'd started modifying the first parameter. Is that an okay requirement, and if not what shall we do about it? Anyway that's my brain dump for today. Thoughts? regards, tom lane Attachments: [text/x-diff] v1-absorb-any-rw-input-parameter.patch (2.0K, 2-v1-absorb-any-rw-input-parameter.patch) download | inline diff: diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c index ea9740e3f8..80b8654fc8 100644 --- a/src/pl/plpgsql/src/pl_exec.c +++ b/src/pl/plpgsql/src/pl_exec.c @@ -532,21 +532,22 @@ plpgsql_exec_function(PLpgSQL_function *func, FunctionCallInfo fcinfo, false); /* - * Force any array-valued parameter to be stored in - * expanded form in our local variable, in hopes of - * improving efficiency of uses of the variable. (This is - * a hack, really: why only arrays? Need more thought - * about which cases are likely to win. See also - * typisarray-specific heuristic in exec_assign_value.) - * - * Special cases: If passed a R/W expanded pointer, assume + * If it's a pass-by-reference type, check to see if we + * received a R/W expanded-object pointer. If so, assume * we can commandeer the object rather than having to copy * it. If passed a R/O expanded pointer, just keep it as * the value of the variable for the moment. (We'll force * it to R/W if the variable gets modified, but that may * very well never happen.) + * + * Also, force any flat array value to be stored in + * expanded form in our local variable, in hopes of + * improving efficiency of uses of the variable. (This is + * a hack, really: why only arrays? Need more thought + * about which cases are likely to win. See also + * typisarray-specific heuristic in exec_assign_value.) */ - if (!var->isnull && var->datatype->typisarray) + if (!var->isnull && var->datatype->typlen == -1) { if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var->value))) { @@ -561,7 +562,7 @@ plpgsql_exec_function(PLpgSQL_function *func, FunctionCallInfo fcinfo, { /* R/O pointer, keep it as-is until assigned to */ } - else + else if (var->datatype->typisarray) { /* flat array, so force to expanded form */ assign_simple_var(&estate, var, ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Using Expanded Objects other than Arrays from plpgsql @ 2024-10-23 04:15 Michel Pelletier <[email protected]> parent: Tom Lane <[email protected]> 0 siblings, 0 replies; 5+ messages in thread From: Michel Pelletier @ 2024-10-23 04:15 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: [email protected] On Tue, Oct 22, 2024 at 12:33 PM Tom Lane <[email protected]> wrote: > Michel Pelletier <[email protected]> writes: > But now we also have > expanded records, and with your use-case as an example of an extension > trying to do similar things, I feel like we have enough examples to > move forward. > Great! As far as the hack we were discussing upthread goes, I realized that > it should test for typlen == -1 not just !typbyval, since the > VARATT_IS_EXTERNAL_EXPANDED_RW test requires that there be a length > word. With that fix and some comment updates, it looks like the > attached. I'm inclined to just go ahead and push that. It won't move > the needle hugely far, but it will help, and it seems simple and safe. > I made those changes and my code works a bit faster, it looks like it takes a couple of the top level expansions out. I'll have more data in the morning. To make more progress, there are basically two areas that we need > to look at: > > 1. exec_assign_value() has hard-wired knowledge that it's a good idea > to expand an array that's being assigned to a plpgsql variable, and > likewise hard-wired knowledge that calling expand_array() is how to > do that. The bit in plpgsql_exec_function() that we're patching > in the attached is the same thing, but for the initial assignment of > a function input parameter to a plpgsql variable. At the time this > was written I was quite unsure that forcible expansion would be a net > win, but the code is nine years old now and there's been few or no > performance complaints. So maybe it's okay to decide that "always > expand expandable types during assignment" is a suitable policy across > the board, and we don't need to figure out a smarter rule. It sounds > like that'd probably be a win for your application, which gives me > more faith in the idea than I would've had before. Definitely a win, as the flattened format of my objects don't have any run time use, so there is no chance for net loss for me. I guess I'm using this feature differently from how arrays are, which have a usable flattened format so there is a need to weigh a trade off with expanding or not. In my case, only the expanded version is useful, and serializing the flat version is expensive. Formalizing something like expand_array would work well for me, as my expand_matrix function has the identical function signature and serves the exact same purpose. So now > I'm thinking that we should steal ideas from the "prosupport" API > (see src/include/nodes/supportnodes.h) and invent a concept of a > "type support" function that can handle an extensible set of > different requests. The first one would be to pass back the > address of an expansion function comparable to expand_array(), > if the type supports being converted to an expanded object. > I'll look into the support code, I haven't seen that before. > 2. Most of the performance gold is hidden in deciding when we > can optimize operations on expanded objects that look like > > plpgsql_var := f(plpgsql_var, other-parameters); > > by passing a R/W rather than R/O expanded pointer to f() and letting > it munge the expanded object in-place. If we fail to do that then > f() has to construct a new expanded object for its result. It's > probably still better off getting a R/O pointer than a flat object, > but nonetheless we fail to avoid a lot of data copying. > > The difficulty here is that we do not want to change the normal naive > semantics of such an assignment, in particular "if f() throws an error > then the value of plpgsql_var has not been modified". This means that > we can only optimize when the R/W parameter is to be passed to the > top-level function of the expression (else, some function called later > could throw an error and ruin things). Furthermore, we need a > guarantee from f() that it will not throw an error after modifying > the value. > As things stand, plpgsql has hard-wired knowledge that > array_subscript_handler(), array_append(), and array_prepend() > are safe in that way, but it knows nothing about anything else. > So one route to making things better seems fairly clear: invent a new > prosupport request that asks whether the function is prepared to make > such a guarantee. I wonder though if you can guarantee any such thing > for your functions, when you are relying on a library that's probably > not designed with such a restriction in mind. If this won't work then > we need a new concept. > This will work for the GraphBLAS API. The expanded object in my case is really just a small box struct around a GraphBLAS "handle" which is an opaque pointer to data which I cannot mutate, only the library can change the object behind the handle. The API makes strong guarantees that it will either do the operation and return a success code or not do the operation and return an error code. It's not possible (normally) to get a corrupt or incomplete object back. > > One idea I was toying with is that it doesn't matter if f() > throws an error so long as the plpgsql function is not executing > within an exception block: if the error propagates out of the plpgsql > function then we no longer care about the value of the variable. > That would very substantially weaken the requirements on how f() > is implemented. I'm not sure that we could make this work across > multiple levels of plpgsql functions (that is, if the value of the > variable ultimately resides in some outer function) but right now > that's not an issue since no plpgsql function as such would ever > promise to be safe, thus it would never receive a R/W pointer to > some outer function's variable. > The water here is pretty deep for me but I'm pretty sure I get what you're saying, I'll need to do some more studying of the plpgsql code which I've been spending the last couple of days familiarizing myself with more. > > same with: > > bfs_vector = vxm(bfs_vector, graph, 'any_secondi_int32', > > w=>bfs_vector, accum=>'min_int32'); > > This matmul mutates bfs_vector, I shouldn't need to reassign it back but > at > > the moment it seems necessary otherwise the mutations are lost but this > > costs a full flatten/expand cycle. > > I'm not hugely excited about that. We could imagine extending > this concept to INOUT parameters of procedures, but it doesn't > seem like that buys anything except a small notational savings. > Maybe it would work to allow multiple parameters of a procedure > to be passed as R/W, whereas we're restricted to one for the > function-notation method. So possibly there's a gain there but > I'm not sure how big. > > BTW, if I understand your example correctly then bfs_vector is > being passed to vxm() twice. Yes, this is not unusual in this form of linear algebra, as multiple operations often accumulate into the same object to prevent a bunch of copying during each iteration of a given algorithm. There is also a "mask" parameter where another or the same object can be provided to either mask in or out (compliment mask) values during the accumulation phase. This is very useful for many algorithms, and good example is the Burkhardt method of Triangle Counting ( https://journals.sagepub.com/doi/10.1177/1473871616666393) which in GraphBLAS boils down to: GrB_mxm (C, A, NULL, semiring, A, A, GrB_DESC_S) ; GrB_reduce (&ntri, NULL, monoid, C, NULL) ; ntri /= 6 ; In this case A is three of the parameters to mxm, the left operand, right operand, and a structural mask. This can be summed up as "A squared, masked by A", which when reduced returns the number of triangles in the graph (times 6). > This brings up an interesting > point: if we pass the first instance as R/W, and vxm() manipulates it, > then the changes would also be visible in its other parameter "w". > This is certainly not per normal semantics. A "safe" function would > have to either not have any possibility that two parameters could > refer to the same object, or be coded in a way that made it impervious > to this issue --- in your example, it couldn't look at "w" anymore > once it'd started modifying the first parameter. Is that an okay > requirement, and if not what shall we do about it? > I *think*, if I understand you correctly, that this isn't an issue for the GraphBLAS. My expanded objects are just boxes around an opaque handle, I don't actually mutate anything inside the box, and I can't see past the opaque pointer. SuiteSparse may be storing the matrix in one of many different formats, or on a GPU, or who knows, all I have is a handle to "A" which I pass to GraphBLAS methods which is the only way I can interact with them. Here's the definition of that vxm function: https://github.com/OneSparse/OneSparse/blob/main/src/matrix.c#L907 It's pretty straightforward, get the arguments, and pass them to the GraphBLAS API, there is no mutable structure inside the expanded "box", just the handle. I'm using the expanded object API to solve my two key problems, flatten an object for disk storage, expand that object (through the GraphBLAS serialize/deserialize API) and turn it into an object handle, which is secretly just a pointer of course to the internal details of the object, but I can't see or change that, only SuiteSparse can. (btw sorry about the bad parameter names, "w" is the name from the API spec which I've been sticking to, which is the optional output object to use, if one is not passed, I create a new one, this is similar to the numpy "out" parameter semantics) . I added some debug instrumentation that might show a bit more of what's going on for me, consider this function: CREATE OR REPLACE FUNCTION test(graph matrix) RETURNS matrix LANGUAGE plpgsql AS $$ DECLARE n bigint = nrows(graph); m bigint = ncols(graph); BEGIN RETURN graph; end; $$; The graph passes straight through but first I call two methods to get the number rows and columns. When I run it on a graph: postgres=# select pg_typeof(test(graph)) from test_graphs ; DEBUG: matrix_nvals DEBUG: DatumGetMatrix DEBUG: expand_matrix DEBUG: new_matrix DEBUG: context_callback_matrix_free DEBUG: matrix_ncols DEBUG: DatumGetMatrix DEBUG: expand_matrix DEBUG: new_matrix DEBUG: context_callback_matrix_free pg_typeof ----------- matrix (1 row) THe matrix gets expanded twice, presumably because the object comes in flat, and both nrows() and ncols() expands it, which ends up being two separate handles and thus two separate objects to the GraphBLAS. Here's another example: CREATE OR REPLACE FUNCTION test2(graph matrix) RETURNS bigint LANGUAGE plpgsql AS $$ BEGIN perform set_element(graph, 1, 1, 1); RETURN nvals(graph); end; $$; CREATE FUNCTION postgres=# select test2(matrix('int32')); DEBUG: new_matrix DEBUG: matrix_get_flat_size DEBUG: flatten_matrix DEBUG: scalar_int32 DEBUG: new_scalar DEBUG: matrix_set_element DEBUG: DatumGetMatrix DEBUG: expand_matrix DEBUG: new_matrix DEBUG: DatumGetScalar DEBUG: matrix_get_flat_size DEBUG: matrix_get_flat_size DEBUG: flatten_matrix DEBUG: context_callback_matrix_free DEBUG: context_callback_scalar_free DEBUG: matrix_nvals DEBUG: DatumGetMatrix DEBUG: expand_matrix DEBUG: new_matrix DEBUG: context_callback_matrix_free DEBUG: context_callback_matrix_free test2 ------- 0 (1 row) I would expect that to return 1. If I do "graph = set_element(graph, 1, 1, 1)" it works. I hope that gives a bit more information about my use cases, in general I'm very happy with the API, it's very algebraic, I have a lot of interesting plans for supporting more operators and subscription syntax, but this issue is not my top priority to see if we can resolve it. I'm sure I missed something in your detailed plan so I'll be going over it some more this week. Please let me know if you have any other questions about my use case or concerns about my expectations. Thank you! -Michel ^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2024-10-23 04:15 UTC | newest] Thread overview: 5+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2024-10-21 03:29 Re: Using Expanded Objects other than Arrays from plpgsql Michel Pelletier <[email protected]> 2024-10-21 03:46 ` Tom Lane <[email protected]> 2024-10-21 17:23 ` Michel Pelletier <[email protected]> 2024-10-22 19:33 ` Tom Lane <[email protected]> 2024-10-23 04:15 ` Michel Pelletier <[email protected]>
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