From: Alvaro Herrera Date: Fri, 2 Dec 2016 03:34:01 +0000 (-0300) Subject: Permit dump/reload of not-too-large >1GB tuples X-Git-Tag: REL9_6_2~105 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=4e01ecae98275298c680c92fdba62daf603dc98e;p=postgresql Permit dump/reload of not-too-large >1GB tuples Our documentation states that our maximum field size is 1 GB, and that our maximum row size of 1.6 TB. However, while this might be attainable in theory with enough contortions, it is not workable in practice; for starters, pg_dump fails to dump tables containing rows larger than 1 GB, even if individual columns are well below the limit; and even if one does manage to manufacture a dump file containing a row that large, the server refuses to load it anyway. This commit enables dumping and reloading of such tuples, provided two conditions are met: 1. no single column is larger than 1 GB (in output size -- for bytea this includes the formatting overhead) 2. the whole row is not larger than 2 GB There are three related changes to enable this: a. StringInfo's API now has two additional functions that allow creating a string that grows beyond the typical 1GB limit (and "long" string). ABI compatibility is maintained. We still limit these strings to 2 GB, though, for reasons explained below. b. COPY now uses long StringInfos, so that pg_dump doesn't choke trying to emit rows longer than 1GB. c. heap_form_tuple now uses the MCXT_ALLOW_HUGE flag in its allocation for the input tuple, which means that large tuples are accepted on input. Note that at this point we do not apply any further limit to the input tuple size. The main reason to limit to 2 GB is that the FE/BE protocol uses 32 bit length words to describe each row; and because the documentation is ambiguous on its signedness and libpq does consider it signed, we cannot use the highest-order bit. Additionally, the StringInfo API uses "int" (which is 4 bytes wide in most platforms) in many places, so we'd need to change that API too in order to improve, which has lots of fallout. Backpatch to 9.5, which is the oldest that has MemoryContextAllocExtended, a necessary piece of infrastructure. We could apply to 9.4 with very minimal additional effort, but any further than that would require backpatching "huge" allocations too. This is the largest set of changes we could find that can be back-patched without breaking compatibility with existing systems. Fixing a bigger set of problems (for example, dumping tuples bigger than 2GB, or dumping fields bigger than 1GB) would require changing the FE/BE protocol and/or changing the StringInfo API in an ABI-incompatible way, neither of which would be back-patchable. Authors: Daniel Vérité, Álvaro Herrera Reviewed by: Tomas Vondra Discussion: https://postgr.es/m/20160229183023.GA286012@alvherre.pgsql --- diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c index 6d0f3f3767..ed9cabd4e0 100644 --- a/src/backend/access/common/heaptuple.c +++ b/src/backend/access/common/heaptuple.c @@ -741,7 +741,9 @@ heap_form_tuple(TupleDesc tupleDescriptor, * Allocate and zero the space needed. Note that the tuple body and * HeapTupleData management structure are allocated in one chunk. */ - tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len); + tuple = MemoryContextAllocExtended(CurrentMemoryContext, + HEAPTUPLESIZE + len, + MCXT_ALLOC_HUGE | MCXT_ALLOC_ZERO); tuple->t_data = td = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE); /* diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c index 5e38edfb70..82bb7aab73 100644 --- a/src/backend/commands/copy.c +++ b/src/backend/commands/copy.c @@ -397,7 +397,7 @@ ReceiveCopyBegin(CopyState cstate) pq_sendint(&buf, format, 2); /* per-column formats */ pq_endmessage(&buf); cstate->copy_dest = COPY_NEW_FE; - cstate->fe_msgbuf = makeStringInfo(); + cstate->fe_msgbuf = makeLongStringInfo(); } else if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 2) { @@ -1903,7 +1903,7 @@ CopyTo(CopyState cstate) cstate->null_print_client = cstate->null_print; /* default */ /* We use fe_msgbuf as a per-row buffer regardless of copy_dest */ - cstate->fe_msgbuf = makeStringInfo(); + cstate->fe_msgbuf = makeLongStringInfo(); /* Get info about the columns we need to process. */ cstate->out_functions = (FmgrInfo *) palloc(num_phys_attrs * sizeof(FmgrInfo)); @@ -2717,8 +2717,8 @@ BeginCopyFrom(Relation rel, cstate->cur_attval = NULL; /* Set up variables to avoid per-attribute overhead. */ - initStringInfo(&cstate->attribute_buf); - initStringInfo(&cstate->line_buf); + initLongStringInfo(&cstate->attribute_buf); + initLongStringInfo(&cstate->line_buf); cstate->line_buf_converted = false; cstate->raw_buf = (char *) palloc(RAW_BUF_SIZE + 1); cstate->raw_buf_index = cstate->raw_buf_len = 0; diff --git a/src/backend/lib/stringinfo.c b/src/backend/lib/stringinfo.c index 7382e08077..b618b37e09 100644 --- a/src/backend/lib/stringinfo.c +++ b/src/backend/lib/stringinfo.c @@ -4,7 +4,8 @@ * * StringInfo provides an indefinitely-extensible string data type. * It can be used to buffer either ordinary C strings (null-terminated text) - * or arbitrary binary data. All storage is allocated with palloc(). + * or arbitrary binary data. All storage is allocated with palloc() and + * friends. * * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California @@ -36,11 +37,29 @@ makeStringInfo(void) return res; } +/* + * makeLongStringInfo + * + * Same as makeStringInfo, for larger strings. + */ +StringInfo +makeLongStringInfo(void) +{ + StringInfo res; + + res = (StringInfo) palloc(sizeof(StringInfoData)); + + initLongStringInfo(res); + + return res; +} + + /* * initStringInfo * * Initialize a StringInfoData struct (with previously undefined contents) - * to describe an empty string. + * to describe an empty string; don't enable long strings yet. */ void initStringInfo(StringInfo str) @@ -49,9 +68,22 @@ initStringInfo(StringInfo str) str->data = (char *) palloc(size); str->maxlen = size; + str->long_ok = false; resetStringInfo(str); } +/* + * initLongStringInfo + * + * Same as initStringInfo, plus enable long strings. + */ +void +initLongStringInfo(StringInfo str) +{ + initStringInfo(str); + str->long_ok = true; +} + /* * resetStringInfo * @@ -142,7 +174,7 @@ appendStringInfoVA(StringInfo str, const char *fmt, va_list args) /* * Return pvsnprintf's estimate of the space needed. (Although this is * given as a size_t, we know it will fit in int because it's not more - * than MaxAllocSize.) + * than either MaxAllocSize or half an int's width.) */ return (int) nprinted; } @@ -244,7 +276,17 @@ appendBinaryStringInfo(StringInfo str, const char *data, int datalen) void enlargeStringInfo(StringInfo str, int needed) { - int newlen; + Size newlen; + Size limit; + + /* + * Determine the upper size limit. Because of overflow concerns outside + * of this module, we limit ourselves to 4-byte signed integer range, + * even for "long_ok" strings. + */ + limit = str->long_ok ? + (((Size) 1) << (sizeof(int32) * 8 - 1)) - 1 : + MaxAllocSize; /* * Guard against out-of-range "needed" values. Without this, we can get @@ -252,7 +294,7 @@ enlargeStringInfo(StringInfo str, int needed) */ if (needed < 0) /* should not happen */ elog(ERROR, "invalid string enlargement request size: %d", needed); - if (((Size) needed) >= (MaxAllocSize - (Size) str->len)) + if (((Size) needed) >= (limit - (Size) str->len)) ereport(ERROR, (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), errmsg("out of memory"), @@ -261,7 +303,7 @@ enlargeStringInfo(StringInfo str, int needed) needed += str->len + 1; /* total space required now */ - /* Because of the above test, we now have needed <= MaxAllocSize */ + /* Because of the above test, we now have needed <= limit */ if (needed <= str->maxlen) return; /* got enough space already */ @@ -276,14 +318,14 @@ enlargeStringInfo(StringInfo str, int needed) newlen = 2 * newlen; /* - * Clamp to MaxAllocSize in case we went past it. Note we are assuming - * here that MaxAllocSize <= INT_MAX/2, else the above loop could - * overflow. We will still have newlen >= needed. + * Clamp to the limit in case we went past it. Note we are assuming here + * that limit <= INT_MAX/2, else the above loop could overflow. We will + * still have newlen >= needed. */ - if (newlen > (int) MaxAllocSize) - newlen = (int) MaxAllocSize; + if (newlen > limit) + newlen = limit; - str->data = (char *) repalloc(str->data, newlen); + str->data = (char *) repalloc_huge(str->data, (Size) newlen); str->maxlen = newlen; } diff --git a/src/include/lib/stringinfo.h b/src/include/lib/stringinfo.h index f64406710e..418d2bc9bb 100644 --- a/src/include/lib/stringinfo.h +++ b/src/include/lib/stringinfo.h @@ -30,6 +30,8 @@ * cursor is initialized to zero by makeStringInfo or initStringInfo, * but is not otherwise touched by the stringinfo.c routines. * Some routines use it to scan through a StringInfo. + * long_ok whether this StringInfo can allocate more than MaxAllocSize + * bytes (but still up to 2GB). *------------------------- */ typedef struct StringInfoData @@ -38,6 +40,7 @@ typedef struct StringInfoData int len; int maxlen; int cursor; + bool long_ok; } StringInfoData; typedef StringInfoData *StringInfo; @@ -46,11 +49,11 @@ typedef StringInfoData *StringInfo; /*------------------------ * There are two ways to create a StringInfo object initially: * - * StringInfo stringptr = makeStringInfo(); + * StringInfo stringptr = makeStringInfo(); // or makeLongStringInfo(); * Both the StringInfoData and the data buffer are palloc'd. * * StringInfoData string; - * initStringInfo(&string); + * initStringInfo(&string); // or initLongStringInfo(); * The data buffer is palloc'd but the StringInfoData is just local. * This is the easiest approach for a StringInfo object that will * only live as long as the current routine. @@ -67,21 +70,26 @@ typedef StringInfoData *StringInfo; /*------------------------ * makeStringInfo - * Create an empty 'StringInfoData' & return a pointer to it. + * makeLongStringInfo + * Create an empty 'StringInfoData' & return a pointer to it. The former + * allows up to 1 GB in size, per palloc(); the latter allows up to 2 GB. */ extern StringInfo makeStringInfo(void); +extern StringInfo makeLongStringInfo(void); /*------------------------ * initStringInfo + * initLongStringInfo * Initialize a StringInfoData struct (with previously undefined contents) - * to describe an empty string. + * to describe an empty string. Size limits as above. */ extern void initStringInfo(StringInfo str); +extern void initLongStringInfo(StringInfo str); /*------------------------ * resetStringInfo * Clears the current content of the StringInfo, if any. The - * StringInfo remains valid. + * StringInfo remains valid. The long_ok flag is not reset. */ extern void resetStringInfo(StringInfo str);