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PostgreSQL 源码解读(195)- 查询#111(排序#4 - 实现)

原创 PostgreSQL 作者:husthxd 时间:2019-05-22 16:29:18 0 删除 编辑

本节继续介绍排序的实现,上一节介绍了tuplesort_begin_heap/tuplesort_puttupleslot,本节介绍的函数是tuplesort_performsort.

一、数据结构

TupleTableSlot
执行器在”tuple table”中存储元组,这个表是各自独立的TupleTableSlots链表.


/*----------
 * The executor stores tuples in a "tuple table" which is a List of
 * independent TupleTableSlots.  There are several cases we need to handle:
 *      1. physical tuple in a disk buffer page
 *      2. physical tuple constructed in palloc'ed memory
 *      3. "minimal" physical tuple constructed in palloc'ed memory
 *      4. "virtual" tuple consisting of Datum/isnull arrays
 * 执行器在"tuple table"中存储元组,这个表是各自独立的TupleTableSlots链表.
 * 有以下情况需要处理:
 *      1. 磁盘缓存页中的物理元组
 *      2. 在已分配内存中构造的物理元组
 *      3. 在已分配内存中构造的"minimal"物理元组
 *      4. 含有Datum/isnull数组的"virtual"虚拟元组
 *
 * The first two cases are similar in that they both deal with "materialized"
 * tuples, but resource management is different.  For a tuple in a disk page
 * we need to hold a pin on the buffer until the TupleTableSlot's reference
 * to the tuple is dropped; while for a palloc'd tuple we usually want the
 * tuple pfree'd when the TupleTableSlot's reference is dropped.
 * 最上面2种情况跟"物化"元组的处理方式类似,但资源管理是不同的.
 * 对于在磁盘页中的元组,需要pin在缓存中直至TupleTableSlot依赖的元组被清除,
 *   而对于通过palloc分配的元组在TupleTableSlot依赖被清除后通常希望使用pfree释放
 *
 * A "minimal" tuple is handled similarly to a palloc'd regular tuple.
 * At present, minimal tuples never are stored in buffers, so there is no
 * parallel to case 1.  Note that a minimal tuple has no "system columns".
 * (Actually, it could have an OID, but we have no need to access the OID.)
 * "minimal"元组与通常的palloc分配的元组处理类似.
 * 截止目前为止,"minimal"元组不会存储在缓存中,因此对于第一种情况不会存在并行的问题.
 * 注意"minimal"没有"system columns"系统列
 * (实际上,可以有OID,但不需要访问OID列)
 *
 * A "virtual" tuple is an optimization used to minimize physical data
 * copying in a nest of plan nodes.  Any pass-by-reference Datums in the
 * tuple point to storage that is not directly associated with the
 * TupleTableSlot; generally they will point to part of a tuple stored in
 * a lower plan node's output TupleTableSlot, or to a function result
 * constructed in a plan node's per-tuple econtext.  It is the responsibility
 * of the generating plan node to be sure these resources are not released
 * for as long as the virtual tuple needs to be valid.  We only use virtual
 * tuples in the result slots of plan nodes --- tuples to be copied anywhere
 * else need to be "materialized" into physical tuples.  Note also that a
 * virtual tuple does not have any "system columns".
 * "virtual"元组是用于在嵌套计划节点中拷贝时最小化物理数据的优化.
 * 所有通过引用传递指向与TupleTableSlot非直接相关的存储的元组的Datums使用,
 *   通常它们会指向存储在低层节点输出的TupleTableSlot中的元组的一部分,
 *   或者指向在计划节点的per-tuple内存上下文econtext中构造的函数结果.
 * 产生计划节点的时候有责任确保这些资源未被释放,确保virtual元组是有效的.
 * 我们使用计划节点中的结果slots中的虚拟元组 --- 元组会拷贝到其他地方需要"物化"到物理元组中.
 * 注意virtual元组不需要有"system columns"
 *
 * It is also possible for a TupleTableSlot to hold both physical and minimal
 * copies of a tuple.  This is done when the slot is requested to provide
 * the format other than the one it currently holds.  (Originally we attempted
 * to handle such requests by replacing one format with the other, but that
 * had the fatal defect of invalidating any pass-by-reference Datums pointing
 * into the existing slot contents.)  Both copies must contain identical data
 * payloads when this is the case.
 * TupleTableSlot包含物理和minimal元组拷贝是可能的.
 * 在slot需要提供格式化而不是当前持有的格式时会出现这种情况.
 * (原始的情况是我们准备通过另外一种格式进行替换来处理这种请求,但在校验引用传递Datums时会出现致命错误)
 * 同时在这种情况下,拷贝必须含有唯一的数据payloads.
 *
 * The Datum/isnull arrays of a TupleTableSlot serve double duty.  When the
 * slot contains a virtual tuple, they are the authoritative data.  When the
 * slot contains a physical tuple, the arrays contain data extracted from
 * the tuple.  (In this state, any pass-by-reference Datums point into
 * the physical tuple.)  The extracted information is built "lazily",
 * ie, only as needed.  This serves to avoid repeated extraction of data
 * from the physical tuple.
 * TupleTableSlot中的Datum/isnull数组有双重职责.
 * 在slot包含虚拟元组时,它们是authoritative(权威)数据.
 * 在slot包含物理元组时,时包含从元组中提取的数据的数组.
 * (在这种情况下,所有通过引用传递的Datums指向物理元组)
 * 提取的信息通过'lazily'在需要的时候才构建.
 * 这样可以避免从物理元组的重复数据提取.
 *
 * A TupleTableSlot can also be "empty", holding no valid data.  This is
 * the only valid state for a freshly-created slot that has not yet had a
 * tuple descriptor assigned to it.  In this state, tts_isempty must be
 * true, tts_shouldFree false, tts_tuple NULL, tts_buffer InvalidBuffer,
 * and tts_nvalid zero.
 * TupleTableSlot可能为"empty",没有有效数据.
 * 对于新鲜创建仍未分配描述的的slot来说这是唯一有效的状态.
 * 在这种状态下,tts_isempty必须为T,tts_shouldFree为F, tts_tuple为NULL,
 *   tts_buffer为InvalidBuffer,tts_nvalid为0.
 *
 * The tupleDescriptor is simply referenced, not copied, by the TupleTableSlot
 * code.  The caller of ExecSetSlotDescriptor() is responsible for providing
 * a descriptor that will live as long as the slot does.  (Typically, both
 * slots and descriptors are in per-query memory and are freed by memory
 * context deallocation at query end; so it's not worth providing any extra
 * mechanism to do more.  However, the slot will increment the tupdesc
 * reference count if a reference-counted tupdesc is supplied.)
 * tupleDescriptor只是简单的引用并没有通过TupleTableSlot中的代码进行拷贝.
 * ExecSetSlotDescriptor()的调用者有责任提供与slot生命周期一样的描述符.
 * (典型的,不管是slots还是描述符会在per-query内存中,
 *  并且会在查询结束时通过内存上下文的析构器释放,因此不需要提供额外的机制来处理.
 *  但是,如果使用了引用计数型tupdesc,slot会增加tupdesc引用计数)
 *
 * When tts_shouldFree is true, the physical tuple is "owned" by the slot
 * and should be freed when the slot's reference to the tuple is dropped.
 * 在tts_shouldFree为T的情况下,物理元组由slot持有,并且在slot引用元组被清除时释放内存.
 *
 * If tts_buffer is not InvalidBuffer, then the slot is holding a pin
 * on the indicated buffer page; drop the pin when we release the
 * slot's reference to that buffer.  (tts_shouldFree should always be
 * false in such a case, since presumably tts_tuple is pointing at the
 * buffer page.)
 * 如tts_buffer不是InvalidBuffer,那么slot持有缓存页中的pin,在释放引用该buffer的slot时会清除该pin.
 * (tts_shouldFree通常来说应为F,因为tts_tuple会指向缓存页)
 *
 * tts_nvalid indicates the number of valid columns in the tts_values/isnull
 * arrays.  When the slot is holding a "virtual" tuple this must be equal
 * to the descriptor's natts.  When the slot is holding a physical tuple
 * this is equal to the number of columns we have extracted (we always
 * extract columns from left to right, so there are no holes).
 * tts_nvalid指示了tts_values/isnull数组中的有效列数.
 * 如果slot含有虚拟元组,该字段必须跟描述符的natts一样.
 * 在slot含有物理元组时,该字段等于我们提取的列数.
 * (我们通常从左到右提取列,因此不会有空洞存在)
 *
 * tts_values/tts_isnull are allocated when a descriptor is assigned to the
 * slot; they are of length equal to the descriptor's natts.
 * 在描述符分配给slot时tts_values/tts_isnull会被分配内存,长度与描述符natts长度一样.
 *
 * tts_mintuple must always be NULL if the slot does not hold a "minimal"
 * tuple.  When it does, tts_mintuple points to the actual MinimalTupleData
 * object (the thing to be pfree'd if tts_shouldFreeMin is true).  If the slot
 * has only a minimal and not also a regular physical tuple, then tts_tuple
 * points at tts_minhdr and the fields of that struct are set correctly
 * for access to the minimal tuple; in particular, tts_minhdr.t_data points
 * MINIMAL_TUPLE_OFFSET bytes before tts_mintuple.  This allows column
 * extraction to treat the case identically to regular physical tuples.
 * 如果slot没有包含minimal元组,tts_mintuple通常必须为NULL.
 * 如含有,则tts_mintuple执行实际的MinimalTupleData对象(如tts_shouldFreeMin为T,则需要通过pfree释放内存).
 * 如果slot只有一个minimal而没有通常的物理元组,那么tts_tuple指向tts_minhdr,
 *   结构体的其他字段会被正确的设置为用于访问minimal元组.
 *   特别的, tts_minhdr.t_data指向tts_mintuple前的MINIMAL_TUPLE_OFFSET字节.
 * 这可以让列提取可以独立处理通常的物理元组.
 *
 * tts_slow/tts_off are saved state for slot_deform_tuple, and should not
 * be touched by any other code.
 * tts_slow/tts_off用于存储slot_deform_tuple状态,不应通过其他代码修改.
 *----------
 */
typedef struct TupleTableSlot
{
    NodeTag     type;//Node标记
    //如slot为空,则为T
    bool        tts_isempty;    /* true = slot is empty */
    //是否需要pfree tts_tuple?
    bool        tts_shouldFree; /* should pfree tts_tuple? */
    //是否需要pfree tts_mintuple?
    bool        tts_shouldFreeMin;  /* should pfree tts_mintuple? */
#define FIELDNO_TUPLETABLESLOT_SLOW 4
    //为slot_deform_tuple存储状态?
    bool        tts_slow;       /* saved state for slot_deform_tuple */
#define FIELDNO_TUPLETABLESLOT_TUPLE 5
    //物理元组,如为虚拟元组则为NULL
    HeapTuple   tts_tuple;      /* physical tuple, or NULL if virtual */
#define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 6
    //slot中的元组描述符
    TupleDesc   tts_tupleDescriptor;    /* slot's tuple descriptor */
    //slot所在的上下文
    MemoryContext tts_mcxt;     /* slot itself is in this context */
    //元组缓存,如无则为InvalidBuffer
    Buffer      tts_buffer;     /* tuple's buffer, or InvalidBuffer */
#define FIELDNO_TUPLETABLESLOT_NVALID 9
    //tts_values中的有效值
    int         tts_nvalid;     /* # of valid values in tts_values */
#define FIELDNO_TUPLETABLESLOT_VALUES 10
    //当前每个属性的值
    Datum      *tts_values;     /* current per-attribute values */
#define FIELDNO_TUPLETABLESLOT_ISNULL 11
    //isnull数组
    bool       *tts_isnull;     /* current per-attribute isnull flags */
    //minimal元组,如无则为NULL
    MinimalTuple tts_mintuple;  /* minimal tuple, or NULL if none */
    //在minimal情况下的工作空间
    HeapTupleData tts_minhdr;   /* workspace for minimal-tuple-only case */
#define FIELDNO_TUPLETABLESLOT_OFF 14
    //slot_deform_tuple的存储状态
    uint32      tts_off;        /* saved state for slot_deform_tuple */
    //不能被变更的描述符(固定描述符)
    bool        tts_fixedTupleDescriptor;   /* descriptor can't be changed */
} TupleTableSlot;
/* base tuple table slot type */
typedef struct TupleTableSlot
{
    NodeTag     type;//Node标记
#define FIELDNO_TUPLETABLESLOT_FLAGS 1
    uint16      tts_flags;      /* 布尔状态;Boolean states */
#define FIELDNO_TUPLETABLESLOT_NVALID 2
    AttrNumber  tts_nvalid;     /* 在tts_values中有多少有效的values;# of valid values in tts_values */
    const TupleTableSlotOps *const tts_ops; /* slot的实际实现;implementation of slot */
#define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 4
    TupleDesc   tts_tupleDescriptor;    /* slot的元组描述符;slot's tuple descriptor */
#define FIELDNO_TUPLETABLESLOT_VALUES 5
    Datum      *tts_values;     /* 当前属性值;current per-attribute values */
#define FIELDNO_TUPLETABLESLOT_ISNULL 6
    bool       *tts_isnull;     /* 当前属性isnull标记;current per-attribute isnull flags */
    MemoryContext tts_mcxt;     /*内存上下文; slot itself is in this context */
} TupleTableSlot;
/* routines for a TupleTableSlot implementation */
//TupleTableSlot的"小程序"
struct TupleTableSlotOps
{
    /* Minimum size of the slot */
    //slot的最小化大小
    size_t          base_slot_size;
    /* Initialization. */
    //初始化方法
    void (*init)(TupleTableSlot *slot);
    /* Destruction. */
    //析构方法
    void (*release)(TupleTableSlot *slot);
    /*
     * Clear the contents of the slot. Only the contents are expected to be
     * cleared and not the tuple descriptor. Typically an implementation of
     * this callback should free the memory allocated for the tuple contained
     * in the slot.
     * 清除slot中的内容。
     * 只希望清除内容,而不希望清除元组描述符。
     * 通常,这个回调的实现应该释放为slot中包含的元组分配的内存。
     */
    void (*clear)(TupleTableSlot *slot);
    /*
     * Fill up first natts entries of tts_values and tts_isnull arrays with
     * values from the tuple contained in the slot. The function may be called
     * with natts more than the number of attributes available in the tuple,
     * in which case it should set tts_nvalid to the number of returned
     * columns.
     * 用slot中包含的元组的值填充tts_values和tts_isnull数组的第一个natts条目。
     * 在调用该函数时,natts可能多于元组中可用属性的数量,在这种情况下,
     *   应该将tts_nvalid设置为返回列的数量。
     */
    void (*getsomeattrs)(TupleTableSlot *slot, int natts);
    /*
     * Returns value of the given system attribute as a datum and sets isnull
     * to false, if it's not NULL. Throws an error if the slot type does not
     * support system attributes.
     * 将给定系统属性的值作为基准返回,如果不为NULL,
     *   则将isnull设置为false。如果slot类型不支持系统属性,则引发错误。
     */
    Datum (*getsysattr)(TupleTableSlot *slot, int attnum, bool *isnull);
    /*
     * Make the contents of the slot solely depend on the slot, and not on
     * underlying resources (like another memory context, buffers, etc).
     * 使slot的内容完全依赖于slot,而不是底层资源(如另一个内存上下文、缓冲区等)。
     */
    void (*materialize)(TupleTableSlot *slot);
    /*
     * Copy the contents of the source slot into the destination slot's own
     * context. Invoked using callback of the destination slot.
     * 将源slot的内容复制到目标slot自己的上下文中。
     * 使用目标slot的回调函数调用。
     */
    void (*copyslot) (TupleTableSlot *dstslot, TupleTableSlot *srcslot);
    /*
     * Return a heap tuple "owned" by the slot. It is slot's responsibility to
     * free the memory consumed by the heap tuple. If the slot can not "own" a
     * heap tuple, it should not implement this callback and should set it as
     * NULL.
     * 返回slot“拥有”的堆元组。
     * slot负责释放堆元组分配的内存。
     * 如果slot不能“拥有”堆元组,它不应该实现这个回调函数,应该将它设置为NULL。
     */
    HeapTuple (*get_heap_tuple)(TupleTableSlot *slot);
    /*
     * Return a minimal tuple "owned" by the slot. It is slot's responsibility
     * to free the memory consumed by the minimal tuple. If the slot can not
     * "own" a minimal tuple, it should not implement this callback and should
     * set it as NULL.
     * 返回slot“拥有”的最小元组。
     * slot负责释放最小元组分配的内存。
     * 如果slot不能“拥有”最小元组,它不应该实现这个回调函数,应该将它设置为NULL。
     */
    MinimalTuple (*get_minimal_tuple)(TupleTableSlot *slot);
    /*
     * Return a copy of heap tuple representing the contents of the slot. The
     * copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibilty to free memory
     * consumed by the slot.
     * 返回表示slot内容的堆元组副本。
     * 需要在当前内存上下文中对副本进行内存分配palloc。
     * 预计slot本身不会受到影响。
     * 它不希望在副本中有有意义的“系统列”。副本不是slot“拥有”的,即调用方必须负责释放slot消耗的内存。
     */
    HeapTuple (*copy_heap_tuple)(TupleTableSlot *slot);
    /*
     * Return a copy of minimal tuple representing the contents of the slot. The
     * copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibilty to free memory
     * consumed by the slot.
     * 返回表示slot内容的最小元组的副本。
     * 需要在当前内存上下文中对副本进行palloc。
     * 预计slot本身不会受到影响。
     * 它不希望在副本中有有意义的“系统列”。副本不是slot“拥有”的,即调用方必须负责释放slot消耗的内存。
     */
    MinimalTuple (*copy_minimal_tuple)(TupleTableSlot *slot);
};
typedef struct tupleDesc
{
    int         natts;          /* tuple中的属性数量;number of attributes in the tuple */
    Oid         tdtypeid;       /* tuple类型的组合类型ID;composite type ID for tuple type */
    int32       tdtypmod;       /* tuple类型的typmode;typmod for tuple type */
    int         tdrefcount;     /* 依赖计数,如为-1,则没有依赖;reference count, or -1 if not counting */
    TupleConstr *constr;        /* 约束,如无则为NULL;constraints, or NULL if none */
    /* attrs[N] is the description of Attribute Number N+1 */
    //attrs[N]是第N+1个属性的描述符
    FormData_pg_attribute attrs[FLEXIBLE_ARRAY_MEMBER];
}  *TupleDesc;

SortState
排序运行期状态信息


/* ----------------
 *     SortState information
 *     排序运行期状态信息
 * ----------------
 */
typedef struct SortState
{
    //基类
    ScanState    ss;                /* its first field is NodeTag */
    //是否需要随机访问排序输出?
    bool        randomAccess;    /* need random access to sort output? */
    //结果集是否存在边界?
    bool        bounded;        /* is the result set bounded? */
    //如存在边界,需要多少个元组?
    int64        bound;            /* if bounded, how many tuples are needed */
    //是否已完成排序?
    bool        sort_Done;        /* sort completed yet? */
    //是否使用有界值?
    bool        bounded_Done;    /* value of bounded we did the sort with */
    //使用的有界值?
    int64        bound_Done;        /* value of bound we did the sort with */
    //tuplesort.c的私有状态
    void       *tuplesortstate; /* private state of tuplesort.c */
    //是否worker?
    bool        am_worker;        /* are we a worker? */
    //每个worker对应一个条目
    SharedSortInfo *shared_info;    /* one entry per worker */
} SortState;
/* ----------------
 *     Shared memory container for per-worker sort information
 *     per-worker排序信息的共享内存容器
 * ----------------
 */
typedef struct SharedSortInfo
{
    //worker个数?
    int            num_workers;
    //排序机制
    TuplesortInstrumentation sinstrument[FLEXIBLE_ARRAY_MEMBER];
} SharedSortInfo;

TuplesortInstrumentation
报告排序统计的数据结构.


/*
 * Data structures for reporting sort statistics.  Note that
 * TuplesortInstrumentation can't contain any pointers because we
 * sometimes put it in shared memory.
 * 报告排序统计的数据结构.
 * 注意TuplesortInstrumentation不能包含指针因为有时候会把该结构体放在共享内存中.
 */
typedef enum
{
    SORT_TYPE_STILL_IN_PROGRESS = 0,//仍然在排序中
    SORT_TYPE_TOP_N_HEAPSORT,//TOP N 堆排序
    SORT_TYPE_QUICKSORT,//快速排序
    SORT_TYPE_EXTERNAL_SORT,//外部排序
    SORT_TYPE_EXTERNAL_MERGE//外部排序后的合并
} TuplesortMethod;//排序方法
typedef enum
{
    SORT_SPACE_TYPE_DISK,//需要用上磁盘
    SORT_SPACE_TYPE_MEMORY//使用内存
} TuplesortSpaceType;
typedef struct TuplesortInstrumentation
{
    //使用的排序算法
    TuplesortMethod sortMethod; /* sort algorithm used */
    //排序使用空间类型
    TuplesortSpaceType spaceType;    /* type of space spaceUsed represents */
    //空间消耗(以K为单位)
    long        spaceUsed;        /* space consumption, in kB */
} TuplesortInstrumentation;

二、源码解读

tuplesort_performsort是排序的实现.


/*
 * All tuples have been provided; finish the sort.
 * 已存在元组,执行排序!
 */
void
tuplesort_performsort(Tuplesortstate *state)
{
    MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
#ifdef TRACE_SORT
    if (trace_sort)
        elog(LOG, "performsort of worker %d starting: %s",
             state->worker, pg_rusage_show(&state->ru_start));
#endif
    //根据状态执行不同的逻辑
    switch (state->status)
    {
        case TSS_INITIAL:
            /*
             * We were able to accumulate all the tuples within the allowed
             * amount of memory, or leader to take over worker tapes
             * 可以在允许的内存大小中积累所有的元组,或者让协调者接管工作tapes.
             */
            if (SERIAL(state))
            {
                /* Just qsort 'em and we're done */
                //快速排序
                tuplesort_sort_memtuples(state);
                state->status = TSS_SORTEDINMEM;
            }
            else if (WORKER(state))
            {
                /*
                 * Parallel workers must still dump out tuples to tape.  No
                 * merge is required to produce single output run, though.
                 * 并行worker必须dump元组到磁盘上.
                 * 但是,生成单个输出运行不需要合并.
                 */
                inittapes(state, false);
                dumptuples(state, true);
                worker_nomergeruns(state);
                state->status = TSS_SORTEDONTAPE;
            }
            else
            {
                /*
                 * Leader will take over worker tapes and merge worker runs.
                 * Note that mergeruns sets the correct state->status.
                 * 并行协调器会接管工作进程的数据并合并工作线程运行.
                 * 注意mergeruns会设置正确的状态:state->status
                 */
                leader_takeover_tapes(state);
                mergeruns(state);
            }
            state->current = 0;
            state->eof_reached = false;
            state->markpos_block = 0L;
            state->markpos_offset = 0;
            state->markpos_eof = false;
            break;
        case TSS_BOUNDED://堆排序
            /*
             * We were able to accumulate all the tuples required for output
             * in memory, using a heap to eliminate excess tuples.  Now we
             * have to transform the heap to a properly-sorted array.
             * 使用堆来消除多余的元组,在内存可以积累所有的元组用于输出.
             * 现在我们必须转换堆为已排序的数组.
             */
            sort_bounded_heap(state);
            state->current = 0;
            state->eof_reached = false;
            state->markpos_offset = 0;
            state->markpos_eof = false;
            state->status = TSS_SORTEDINMEM;
            break;
        case TSS_BUILDRUNS:
            /*
             * Finish tape-based sort.  First, flush all tuples remaining in
             * memory out to tape; then merge until we have a single remaining
             * run (or, if !randomAccess and !WORKER(), one run per tape).
             * Note that mergeruns sets the correct state->status.
             * 完成tape-based排序.
             * 首先刷新所有在内存的元组到tape(持久化存储)上,然后合并直至只留下一个在运行.
             * (否则,如果!randomAccess 且 !WORKER(),一个tape运行一次)
             */
            //全部刷到磁盘上
            dumptuples(state, true);
            //合并执行
            mergeruns(state);
            state->eof_reached = false;
            state->markpos_block = 0L;
            state->markpos_offset = 0;
            state->markpos_eof = false;
            break;
        default:
            elog(ERROR, "invalid tuplesort state");
            break;
    }
#ifdef TRACE_SORT
    if (trace_sort)
    {
        if (state->status == TSS_FINALMERGE)
            elog(LOG, "performsort of worker %d done (except %d-way final merge): %s",
                 state->worker, state->activeTapes,
                 pg_rusage_show(&state->ru_start));
        else
            elog(LOG, "performsort of worker %d done: %s",
                 state->worker, pg_rusage_show(&state->ru_start));
    }
#endif
    MemoryContextSwitchTo(oldcontext);
}

三、跟踪分析

测试脚本


select * from t_sort order by c1,c2;

跟踪分析


(gdb) b tuplesort_begin_heap
Breakpoint 1 at 0xa6ffa1: file tuplesort.c, line 812.
(gdb) b tuplesort_puttupleslot
Breakpoint 2 at 0xa7119d: file tuplesort.c, line 1436.
(gdb) b tuplesort_performsort
Breakpoint 3 at 0xa71f45: file tuplesort.c, line 1792.
(gdb) c
Continuing.
Breakpoint 1, tuplesort_begin_heap (tupDesc=0x208fa40, nkeys=2, attNums=0x2081858, sortOperators=0x2081878, 
    sortCollations=0x2081898, nullsFirstFlags=0x20818b8, workMem=4096, coordinate=0x0, randomAccess=false)
    at tuplesort.c:812
812        Tuplesortstate *state = tuplesort_begin_common(workMem, coordinate,
(gdb)

tuplesort_begin_heap
输入参数


(gdb) p *tupDesc
$1 = {natts = 7, tdtypeid = 2249, tdtypmod = -1, tdhasoid = false, tdrefcount = -1, constr = 0x0, attrs = 0x208fa60}
(gdb) p *tupDesc->attrs
$2 = {attrelid = 0, attname = {data = '\000' <repeats 63 times>}, atttypid = 1043, attstattarget = -1, attlen = -1, 
  attnum = 1, attndims = 0, attcacheoff = -1, atttypmod = 24, attbyval = false, attstorage = 120 'x', attalign = 105 'i', 
  attnotnull = false, atthasdef = false, atthasmissing = false, attidentity = 0 '\000', attisdropped = false, 
  attislocal = true, attinhcount = 0, attcollation = 100}
(gdb) p *attNums
$3 = 2
(gdb) p *sortOperators
$4 = 97
(gdb) p *sortCollations
$5 = 0
(gdb) p nullsFirstFlags
$6 = (_Bool *) 0x20818b8
(gdb) p *nullsFirstFlags
$7 = false
(gdb)

获取排序状态,status = TSS_INITIAL


(gdb) p *state
$8 = {status = TSS_INITIAL, nKeys = 0, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0x0, copytup = 0x0, writetup = 0x0, readtup = 0x0, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x0, sortKeys = 0x0, onlyKey = 0x0, abbrevNext = 0, indexInfo = 0x0, estate = 0x0, 
  heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, datumType = 0, 
  datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, ru_stime = {
        tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}

设置运行状态


(gdb) n
819        AssertArg(nkeys > 0);
(gdb) 
822        if (trace_sort)
(gdb) 
828        state->nKeys = nkeys;
(gdb) 
830        TRACE_POSTGRESQL_SORT_START(HEAP_SORT,
(gdb) 
837        state->comparetup = comparetup_heap;
(gdb) 
838        state->copytup = copytup_heap;
(gdb) 
839        state->writetup = writetup_heap;
(gdb) 
840        state->readtup = readtup_heap;
(gdb) 
842        state->tupDesc = tupDesc;    /* assume we need not copy tupDesc */
(gdb) 
843        state->abbrevNext = 10;
(gdb) 
846        state->sortKeys = (SortSupport) palloc0(nkeys * sizeof(SortSupportData));
(gdb) 
848        for (i = 0; i < nkeys; i++)
(gdb) p *state
$9 = {status = TSS_INITIAL, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0xa7525b <comparetup_heap>, copytup = 0xa76247 <copytup_heap>, 
  writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, 
  estate = 0x0, heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, 
  datumType = 0, datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, 
      ru_stime = {tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb)

为每一列(c1&c2)准备SortSupport数据(分配内存空间)


(gdb) n
850            SortSupport sortKey = state->sortKeys + i;
(gdb) 
852            AssertArg(attNums[i] != 0);
(gdb) p *state->sortKeys
$10 = {ssup_cxt = 0x0, ssup_collation = 0, ssup_reverse = false, ssup_nulls_first = false, ssup_attno = 0, 
  ssup_extra = 0x0, comparator = 0x0, abbreviate = false, abbrev_converter = 0x0, abbrev_abort = 0x0, 
  abbrev_full_comparator = 0x0}
(gdb) n
853            AssertArg(sortOperators[i] != 0);
(gdb) 
855            sortKey->ssup_cxt = CurrentMemoryContext;
(gdb) 
856            sortKey->ssup_collation = sortCollations[i];
(gdb) 
857            sortKey->ssup_nulls_first = nullsFirstFlags[i];
(gdb) 
858            sortKey->ssup_attno = attNums[i];
(gdb) 
860            sortKey->abbreviate = (i == 0);
(gdb) 
862            PrepareSortSupportFromOrderingOp(sortOperators[i], sortKey);
(gdb) 
848        for (i = 0; i < nkeys; i++)
(gdb) 
850            SortSupport sortKey = state->sortKeys + i;
(gdb) 
852            AssertArg(attNums[i] != 0);
(gdb) 
853            AssertArg(sortOperators[i] != 0);
(gdb) 
855            sortKey->ssup_cxt = CurrentMemoryContext;
(gdb) 
856            sortKey->ssup_collation = sortCollations[i];
(gdb) 
857            sortKey->ssup_nulls_first = nullsFirstFlags[i];
(gdb) 
858            sortKey->ssup_attno = attNums[i];
(gdb) 
860            sortKey->abbreviate = (i == 0);
(gdb) 
862            PrepareSortSupportFromOrderingOp(sortOperators[i], sortKey);
(gdb) 
848        for (i = 0; i < nkeys; i++)
(gdb)

完成初始化,返回state


(gdb) 
871        if (nkeys == 1 && !state->sortKeys->abbrev_converter)
(gdb) n
874        MemoryContextSwitchTo(oldcontext);
(gdb) 
876        return state;
(gdb) p *state
$11 = {status = TSS_INITIAL, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0xa7525b <comparetup_heap>, copytup = 0xa76247 <copytup_heap>, 
  writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, 
  estate = 0x0, heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, 
  datumType = 0, datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, 
      ru_stime = {tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb)

tuplesort_puttupleslot
出现在循环中


        for (;;)
        {
            //从outer plan中获取元组
            slot = ExecProcNode(outerNode);
            if (TupIsNull(slot))
                break;//直至全部获取完毕
            //排序
            tuplesort_puttupleslot(tuplesortstate, slot);
        }

以其中一个slot为例说明


(gdb) c
Continuing.
Breakpoint 2, tuplesort_puttupleslot (state=0x20933a8, slot=0x208f8c8) at tuplesort.c:1436
1436        MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);

输入参数,state为先前调用begin_heap返回的state,slot为outer node返回的元组slot


(gdb) p *slot
$12 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false, 
  tts_tuple = 0x2090678, tts_tupleDescriptor = 0x7f061a300380, tts_mcxt = 0x208f270, tts_buffer = 103, tts_nvalid = 0, 
  tts_values = 0x208f928, tts_isnull = 0x208f960, tts_mintuple = 0x0, tts_minhdr = {t_len = 0, t_self = {ip_blkid = {
        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x0}, tts_off = 0, tts_fixedTupleDescriptor = true}
(gdb)

slot中的元组数据


(gdb) p *slot->tts_values
$13 = 0
(gdb) p *slot->tts_tuple
$14 = {t_len = 56, t_self = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 1}, t_tableOid = 286759, t_data = 0x7f05ee0c4648}
(gdb) p *slot->tts_tuple->t_data
$15 = {t_choice = {t_heap = {t_xmin = 839, t_xmax = 0, t_field3 = {t_cid = 0, t_xvac = 0}}, t_datum = {datum_len_ = 839, 
      datum_typmod = 0, datum_typeid = 0}}, t_ctid = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 1}, t_infomask2 = 7, 
  t_infomask = 2306, t_hoff = 24 '\030', t_bits = 0x7f05ee0c465f ""}
(gdb) p *slot->tts_tuple->t_data->t_bits
$16 = 0 '\000'
(gdb) x/16ux *slot->tts_tuple->t_data->t_bits
0x0:    Cannot access memory at address 0x0
(gdb) x/16ux slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:    0x5a470b00    0x00003130    0x00000100    0x00000100
0x7f05ee0c466f:    0x00000100    0x00000100    0x00000100    0x00000100
0x7f05ee0c467f:    0x00000000    0x8f282800    0x000000da    0x40023800
0x7f05ee0c468f:    0x04200002    0x00000020    0x709fc800    0x709f9000
(gdb) x/16bx slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:    0x00    0x0b    0x47    0x5a    0x30    0x31    0x00    0x00
0x7f05ee0c4667:    0x00    0x01    0x00    0x00    0x00    0x01    0x00    0x00
(gdb) x/16bc slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:    0 '\000'    11 '\v'    71 'G'    90 'Z'    48 '0'    49 '1'    0 '\000'    0 '\000'
0x7f05ee0c4667:    0 '\000'    1 '\001'    0 '\000'    0 '\000'    0 '\000'    1 '\001'    0 '\000'    0 '\000'
(gdb) p *slot->tts_tupleDescriptor
$17 = {natts = 7, tdtypeid = 286761, tdtypmod = -1, tdhasoid = false, tdrefcount = 2, constr = 0x0, attrs = 0x7f061a3003a0}
(gdb) p *slot
$18 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false, 
  tts_tuple = 0x2090678, tts_tupleDescriptor = 0x7f061a300380, tts_mcxt = 0x208f270, tts_buffer = 103, tts_nvalid = 0, 
  tts_values = 0x208f928, tts_isnull = 0x208f960, tts_mintuple = 0x0, tts_minhdr = {t_len = 0, t_self = {ip_blkid = {
        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x0}, tts_off = 0, tts_fixedTupleDescriptor = true}
(gdb) p *slot->tts_values[0]
Cannot access memory at address 0x0
(gdb) p slot->tts_values[0]
$19 = 0
(gdb) x/32bc slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:    0 '\000'    11 '\v'    71 'G'    90 'Z'    48 '0'    49 '1'    0 '\000'    0 '\000'
0x7f05ee0c4667:    0 '\000'    1 '\001'    0 '\000'    0 '\000'    0 '\000'    1 '\001'    0 '\000'    0 '\000'
0x7f05ee0c466f:    0 '\000'    1 '\001'    0 '\000'    0 '\000'    0 '\000'    1 '\001'    0 '\000'    0 '\000'
0x7f05ee0c4677:    0 '\000'    1 '\001'    0 '\000'    0 '\000'    0 '\000'    1 '\001'    0 '\000'    0 '\000'
(gdb) x/32bx slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:    0x00    0x0b    0x47    0x5a    0x30    0x31    0x00    0x00
0x7f05ee0c4667:    0x00    0x01    0x00    0x00    0x00    0x01    0x00    0x00
0x7f05ee0c466f:    0x00    0x01    0x00    0x00    0x00    0x01    0x00    0x00
0x7f05ee0c4677:    0x00    0x01    0x00    0x00    0x00    0x01    0x00    0x00

拷贝元组,并放到state->memtuples中


(gdb) n
1443        COPYTUP(state, &stup, (void *) slot);
(gdb) 
1445        puttuple_common(state, &stup);
(gdb) step
puttuple_common (state=0x20933a8, tuple=0x7ffe890e0b00) at tuplesort.c:1639
1639        Assert(!LEADER(state));
(gdb) n
1641        switch (state->status)
(gdb) p state->status
$20 = TSS_INITIAL
(gdb) n
1652                if (state->memtupcount >= state->memtupsize - 1)
(gdb) p state->memtupcount
$21 = 0
(gdb) p state->memtupsize - 1
$22 = 1023
(gdb) n
1657                state->memtuples[state->memtupcount++] = *tuple;
(gdb) 
1671                if (state->bounded &&
(gdb) p state->bounded
$23 = false
(gdb) n
1688                if (state->memtupcount < state->memtupsize && !LACKMEM(state))
(gdb) 
1689                    return;
(gdb) 
1743    }
(gdb) 
tuplesort_puttupleslot (state=0x20933a8, slot=0x208f8c8) at tuplesort.c:1447
1447        MemoryContextSwitchTo(oldcontext);
(gdb) 
1448    }
(gdb) 
(gdb) p state->memtuples[0]
$25 = {tuple = 0x20993d8, datum1 = 1, isnull1 = false, tupindex = 0}

tuplesort_performsort


(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x0000000000a6ffa1 in tuplesort_begin_heap at tuplesort.c:812
    breakpoint already hit 1 time
2       breakpoint     keep y   0x0000000000a7119d in tuplesort_puttupleslot at tuplesort.c:1436
    breakpoint already hit 1 time
3       breakpoint     keep y   0x0000000000a71f45 in tuplesort_performsort at tuplesort.c:1792
(gdb) del 2
(gdb) c
Continuing.
Breakpoint 3, tuplesort_performsort (state=0x20933a8) at tuplesort.c:1792
1792        MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
(gdb)

输入参数


(gdb) p *state
$27 = {status = TSS_BUILDRUNS, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, 
  tuples = true, availMem = 824360, allowedMem = 4194304, maxTapes = 16, tapeRange = 15, sortcontext = 0x2093290, 
  tuplecontext = 0x20992c0, tapeset = 0x2093a00, comparetup = 0xa7525b <comparetup_heap>, 
  copytup = 0xa76247 <copytup_heap>, writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, 
  memtuples = 0x2611570, memtupcount = 26592, memtupsize = 37448, growmemtuples = false, slabAllocatorUsed = false, 
  slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, 
  currentRun = 2, mergeactive = 0x2093878, Level = 1, destTape = 2, tp_fib = 0x20938a0, tp_runs = 0x20938f8, 
  tp_dummy = 0x2093950, tp_tapenum = 0x20939a8, activeTapes = 0, result_tape = -1, current = 0, eof_reached = false, 
  markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, nParticipants = -1, 
  tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, estate = 0x0, heapRel = 0x0, 
  indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, datumType = 0, datumTypeLen = 0, 
  ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, ru_stime = {tv_sec = 0, 
        tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {ru_idrss = 0, 
        __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {ru_majflt = 0, 
        __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, {
        ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb) p state->memtupsize
$28 = 37448
(gdb)

state->status状态已切换为TSS_BUILDRUNS


(gdb) n
1795        if (trace_sort)
(gdb) 
1800        switch (state->status)
(gdb) p state->status
$29 = TSS_BUILDRUNS
(gdb)

全部刷到磁盘上,归并排序


(gdb) n
1864                dumptuples(state, true);
(gdb) 
1865                mergeruns(state);
(gdb) 
1866                state->eof_reached = false;
(gdb) 
1867                state->markpos_block = 0L;
(gdb) 
1868                state->markpos_offset = 0;
(gdb) 
1869                state->markpos_eof = false;
(gdb) 
1870                break;
(gdb) 
1878        if (trace_sort)
(gdb) 
1890        MemoryContextSwitchTo(oldcontext);
(gdb) 
1891    }
(gdb)

DONE!

四、参考资料

N/A

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/6906/viewspace-2645213/,如需转载,请注明出处,否则将追究法律责任。

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长期从事政务、金融等行业产品研发和架构设计工作,ITPUB数据库版块资深版主,对Oracle、PostgreSQL有深入研究。现就职于广州云图数据技术有限公司,系统架构师。

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