Attached is an updated patch of PQresultMemsize(). The implementation is unchanged, but I added SGML documentation about this new function.
I'd be pleased about comments to adding this to libpq. -- Kind Regards, Lars
From 766a7f2381ae6c9d442a7359cabc58515186f8c4 Mon Sep 17 00:00:00 2001 From: Lars Kanis <l...@greiz-reinsdorf.de> Date: Sat, 23 Jun 2018 19:34:11 +0200 Subject: [PATCH] libpq: Add function PQresultMemsize() This function retrieves the number of bytes allocated for a given result. That can be used to instruct the GC about the memory consumed behind a wrapping object and for diagnosing memory consumption. This is an alternative approach to customizable malloc/realloc/free functions as discussed here: https://www.postgresql.org/message-id/flat/20170828172834.GA71455%40TC.local#20170828172834.GA71455@TC.local --- doc/src/sgml/libpq.sgml | 28 ++++++++++++++++++++++++++++ src/interfaces/libpq/exports.txt | 1 + src/interfaces/libpq/fe-exec.c | 14 +++++++++++++- src/interfaces/libpq/libpq-fe.h | 1 + src/interfaces/libpq/libpq-int.h | 2 ++ 5 files changed, 45 insertions(+), 1 deletion(-) diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml index d67212b831..c573c79ae3 100644 --- a/doc/src/sgml/libpq.sgml +++ b/doc/src/sgml/libpq.sgml @@ -6384,6 +6384,34 @@ void *PQresultAlloc(PGresult *res, size_t nBytes); </listitem> </varlistentry> + <varlistentry id="libpq-pqresultmemsize"> + <term> + <function>PQresultMemsize</function> + <indexterm> + <primary>PQresultMemsize</primary> + </indexterm> + </term> + + <listitem> + <para> + Retrieves the number of bytes allocated for a <structname>PGresult</structname> object. +<synopsis> +size_t PQresultMemsize(const PGresult *res); +</synopsis> + </para> + + <para> + The number of bytes includes the memory allocated for the PGresult itself, + memory to store data from the server, required internal metadata of a + PGresult object and data allocated by <function>PQresultAlloc</function>. + That is to say all memory which gets freed by <function>PQclear</function>. + + This information can be used for diagnosing memory consumption and to instruct + a garbage collector about the memory consumed behind a wrapping object. + </para> + </listitem> + </varlistentry> + <varlistentry id="libpq-pqlibversion"> <term> <function>PQlibVersion</function> diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt index d6a38d0df8..0b50dddbb7 100644 --- a/src/interfaces/libpq/exports.txt +++ b/src/interfaces/libpq/exports.txt @@ -172,3 +172,4 @@ PQsslAttribute 169 PQsetErrorContextVisibility 170 PQresultVerboseErrorMessage 171 PQencryptPasswordConn 172 +PQresultMemsize 173 diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c index 4c0114c514..064c7a693c 100644 --- a/src/interfaces/libpq/fe-exec.c +++ b/src/interfaces/libpq/fe-exec.c @@ -166,6 +166,7 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status) result->curBlock = NULL; result->curOffset = 0; result->spaceLeft = 0; + result->memsize = sizeof(PGresult); if (conn) { @@ -215,6 +216,12 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status) return result; } +size_t +PQresultMemsize(const PGresult *res) +{ + return res->memsize; +} + /* * PQsetResultAttrs * @@ -567,9 +574,11 @@ pqResultAlloc(PGresult *res, size_t nBytes, bool isBinary) */ if (nBytes >= PGRESULT_SEP_ALLOC_THRESHOLD) { - block = (PGresult_data *) malloc(nBytes + PGRESULT_BLOCK_OVERHEAD); + size_t alloc_size = nBytes + PGRESULT_BLOCK_OVERHEAD; + block = (PGresult_data *) malloc(alloc_size); if (!block) return NULL; + res->memsize += alloc_size; space = block->space + PGRESULT_BLOCK_OVERHEAD; if (res->curBlock) { @@ -594,6 +603,7 @@ pqResultAlloc(PGresult *res, size_t nBytes, bool isBinary) block = (PGresult_data *) malloc(PGRESULT_DATA_BLOCKSIZE); if (!block) return NULL; + res->memsize += PGRESULT_DATA_BLOCKSIZE; block->next = res->curBlock; res->curBlock = block; if (isBinary) @@ -711,6 +721,7 @@ PQclear(PGresult *res) res->errFields = NULL; res->events = NULL; res->nEvents = 0; + res->memsize = 0; /* res->curBlock was zeroed out earlier */ /* Free the PGresult structure itself */ @@ -927,6 +938,7 @@ pqAddTuple(PGresult *res, PGresAttValue *tup, const char **errmsgp) realloc(res->tuples, newSize * sizeof(PGresAttValue *)); if (!newTuples) return false; /* malloc or realloc failed */ + res->memsize += (newSize - res->tupArrSize) * sizeof(PGresAttValue *); res->tupArrSize = newSize; res->tuples = newTuples; } diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h index ed9c806861..4fd9a4fcda 100644 --- a/src/interfaces/libpq/libpq-fe.h +++ b/src/interfaces/libpq/libpq-fe.h @@ -491,6 +491,7 @@ extern int PQgetlength(const PGresult *res, int tup_num, int field_num); extern int PQgetisnull(const PGresult *res, int tup_num, int field_num); extern int PQnparams(const PGresult *res); extern Oid PQparamtype(const PGresult *res, int param_num); +extern size_t PQresultMemsize(const PGresult *res); /* Describe prepared statements and portals */ extern PGresult *PQdescribePrepared(PGconn *conn, const char *stmt); diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h index 9a586ff25a..37c9c3853d 100644 --- a/src/interfaces/libpq/libpq-int.h +++ b/src/interfaces/libpq/libpq-int.h @@ -208,6 +208,8 @@ struct pg_result PGresult_data *curBlock; /* most recently allocated block */ int curOffset; /* start offset of free space in block */ int spaceLeft; /* number of free bytes remaining in block */ + + size_t memsize; /* Number of bytes of all memory allocated for this result */ }; /* PGAsyncStatusType defines the state of the query-execution state machine */ -- 2.17.1
